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Schwenkert S, Lo WT, Szulc B, Yip CK, Pratt AI, Cusack SA, Brandt B, Leister D, Kunz HH. Probing the physiological role of the plastid outer-envelope membrane using the oemiR plasmid collection. G3 (BETHESDA, MD.) 2023; 13:jkad187. [PMID: 37572358 PMCID: PMC10542568 DOI: 10.1093/g3journal/jkad187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 07/20/2023] [Accepted: 08/04/2023] [Indexed: 08/14/2023]
Abstract
Plastids are the site of complex biochemical pathways, most prominently photosynthesis. The organelle evolved through endosymbiosis with a cyanobacterium, which is exemplified by the outer envelope membrane that harbors more than 40 proteins in Arabidopsis. Their evolutionary conservation indicates high significance for plant cell function. While a few proteins are well-studied as part of the protein translocon complex the majority of outer envelope protein functions is unclear. Gaining a deeper functional understanding has been complicated by the lack of observable loss-of-function mutant phenotypes, which is often rooted in functional genetic redundancy. Therefore, we designed outer envelope-specific artificial micro RNAs (oemiRs) capable of downregulating transcripts from several loci simultaneously. We successfully tested oemiR function by performing a proof-of-concept screen for pale and cold-sensitive mutants. An in-depth analysis of pale mutant alleles deficient in the translocon component TOC75 using proteomics provided new insights into putative compensatory import pathways. The cold stress screen not only recapitulated 3 previously known phenotypes of cold-sensitive mutants but also identified 4 mutants of additional oemiR outer envelope loci. Altogether our study revealed a role of the outer envelope to tolerate cold conditions and showcasts the power of the oemiR collection to research the significance of outer envelope proteins.
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Affiliation(s)
- Serena Schwenkert
- Plant Molecular Biology, Faculty of Biology, Ludwig-Maximilians-Universität Munich, 82152 Planegg-Martinsried, Germany
| | - Wing Tung Lo
- Plant Molecular Biology, Faculty of Biology, Ludwig-Maximilians-Universität Munich, 82152 Planegg-Martinsried, Germany
| | - Beata Szulc
- Plant Biochemistry, Faculty of Biology, Ludwig-Maximilians-Universität Munich, 82152 Planegg-Martinsried, Germany
| | - Chun Kwan Yip
- Plant Molecular Biology, Faculty of Biology, Ludwig-Maximilians-Universität Munich, 82152 Planegg-Martinsried, Germany
| | - Anna I Pratt
- School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164-4236, USA
| | | | - Benjamin Brandt
- Plant Biochemistry, Faculty of Biology, Ludwig-Maximilians-Universität Munich, 82152 Planegg-Martinsried, Germany
| | - Dario Leister
- Plant Molecular Biology, Faculty of Biology, Ludwig-Maximilians-Universität Munich, 82152 Planegg-Martinsried, Germany
| | - Hans-Henning Kunz
- Plant Biochemistry, Faculty of Biology, Ludwig-Maximilians-Universität Munich, 82152 Planegg-Martinsried, Germany
- School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA 99164-4236, USA
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2
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Christian R, Labbancz J, Usadel B, Dhingra A. Understanding protein import in diverse non-green plastids. Front Genet 2023; 14:969931. [PMID: 37007964 PMCID: PMC10063809 DOI: 10.3389/fgene.2023.969931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 02/24/2023] [Indexed: 03/19/2023] Open
Abstract
The spectacular diversity of plastids in non-green organs such as flowers, fruits, roots, tubers, and senescing leaves represents a Universe of metabolic processes in higher plants that remain to be completely characterized. The endosymbiosis of the plastid and the subsequent export of the ancestral cyanobacterial genome to the nuclear genome, and adaptation of the plants to all types of environments has resulted in the emergence of diverse and a highly orchestrated metabolism across the plant kingdom that is entirely reliant on a complex protein import and translocation system. The TOC and TIC translocons, critical for importing nuclear-encoded proteins into the plastid stroma, remain poorly resolved, especially in the case of TIC. From the stroma, three core pathways (cpTat, cpSec, and cpSRP) may localize imported proteins to the thylakoid. Non-canonical routes only utilizing TOC also exist for the insertion of many inner and outer membrane proteins, or in the case of some modified proteins, a vesicular import route. Understanding this complex protein import system is further compounded by the highly heterogeneous nature of transit peptides, and the varying transit peptide specificity of plastids depending on species and the developmental and trophic stage of the plant organs. Computational tools provide an increasingly sophisticated means of predicting protein import into highly diverse non-green plastids across higher plants, which need to be validated using proteomics and metabolic approaches. The myriad plastid functions enable higher plants to interact and respond to all kinds of environments. Unraveling the diversity of non-green plastid functions across the higher plants has the potential to provide knowledge that will help in developing climate resilient crops.
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Affiliation(s)
- Ryan Christian
- Department of Horticulture, Washington State University, Pullman, WA, United States
| | - June Labbancz
- Department of Horticulture, Washington State University, Pullman, WA, United States
- Department of Horticultural Sciences, Texas A&M University, College Station, TX, United States
| | | | - Amit Dhingra
- Department of Horticulture, Washington State University, Pullman, WA, United States
- Department of Horticultural Sciences, Texas A&M University, College Station, TX, United States
- *Correspondence: Amit Dhingra,
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Culver JA, Li X, Jordan M, Mariappan M. A second chance for protein targeting/folding: Ubiquitination and deubiquitination of nascent proteins. Bioessays 2022; 44:e2200014. [PMID: 35357021 PMCID: PMC9133216 DOI: 10.1002/bies.202200014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 03/09/2022] [Accepted: 03/10/2022] [Indexed: 11/07/2022]
Abstract
Molecular chaperones in cells constantly monitor and bind to exposed hydrophobicity in newly synthesized proteins and assist them in folding or targeting to cellular membranes for insertion. However, proteins can be misfolded or mistargeted, which often causes hydrophobic amino acids to be exposed to the aqueous cytosol. Again, chaperones recognize exposed hydrophobicity in these proteins to prevent nonspecific interactions and aggregation, which are harmful to cells. The chaperone-bound misfolded proteins are then decorated with ubiquitin chains denoting them for proteasomal degradation. It remains enigmatic how molecular chaperones can mediate both maturation of nascent proteins and ubiquitination of misfolded proteins solely based on their exposed hydrophobic signals. In this review, we propose a dynamic ubiquitination and deubiquitination model in which ubiquitination of newly synthesized proteins serves as a "fix me" signal for either refolding of soluble proteins or retargeting of membrane proteins with the help of chaperones and deubiquitinases. Such a model would provide additional time for aberrant nascent proteins to fold or route for membrane insertion, thus avoiding excessive protein degradation and saving cellular energy spent on protein synthesis. Also see the video abstract here: https://youtu.be/gkElfmqaKG4.
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Affiliation(s)
- Jacob A. Culver
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
| | - Xia Li
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
| | - Matthew Jordan
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
| | - Malaiyalam Mariappan
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale West Campus, West Haven, CT 06516, USA
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4
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New Insights into the Chloroplast Outer Membrane Proteome and Associated Targeting Pathways. Int J Mol Sci 2022; 23:ijms23031571. [PMID: 35163495 PMCID: PMC8836251 DOI: 10.3390/ijms23031571] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 01/24/2022] [Accepted: 01/27/2022] [Indexed: 12/04/2022] Open
Abstract
Plastids are a dynamic class of organelle in plant cells that arose from an ancient cyanobacterial endosymbiont. Over the course of evolution, most genes encoding plastid proteins were transferred to the nuclear genome. In parallel, eukaryotic cells evolved a series of targeting pathways and complex proteinaceous machinery at the plastid surface to direct these proteins back to their target organelle. Chloroplasts are the most well-characterized plastids, responsible for photosynthesis and other important metabolic functions. The biogenesis and function of chloroplasts rely heavily on the fidelity of intracellular protein trafficking pathways. Therefore, understanding these pathways and their regulation is essential. Furthermore, the chloroplast outer membrane proteome remains relatively uncharted territory in our understanding of protein targeting. Many key players in the cytosol, receptors at the organelle surface, and insertases that facilitate insertion into the chloroplast outer membrane remain elusive for this group of proteins. In this review, we summarize recent advances in the understanding of well-characterized chloroplast outer membrane protein targeting pathways as well as provide new insights into novel targeting signals and pathways more recently identified using a bioinformatic approach. As a result of our analyses, we expand the known number of chloroplast outer membrane proteins from 117 to 138.
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Mehlhorn DG, Asseck LY, Grefen C. Looking for a safe haven: tail-anchored proteins and their membrane insertion pathways. PLANT PHYSIOLOGY 2021; 187:1916-1928. [PMID: 35235667 PMCID: PMC8644595 DOI: 10.1093/plphys/kiab298] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 06/05/2021] [Indexed: 06/14/2023]
Abstract
Insertion of membrane proteins into the lipid bilayer is a crucial step during their biosynthesis. Eukaryotic cells face many challenges in directing these proteins to their predestined target membrane. The hydrophobic signal peptide or transmembrane domain (TMD) of the nascent protein must be shielded from the aqueous cytosol and its target membrane identified followed by transport and insertion. Components that evolved to deal with each of these challenging steps range from chaperones to receptors, insertases, and sophisticated translocation complexes. One prominent translocation pathway for most proteins is the signal recognition particle (SRP)-dependent pathway which mediates co-translational translocation of proteins across or into the endoplasmic reticulum (ER) membrane. This textbook example of protein insertion is stretched to its limits when faced with secretory or membrane proteins that lack an amino-terminal signal sequence or TMD. Particularly, a large group of so-called tail-anchored (TA) proteins that harbor a single carboxy-terminal TMD require an alternative, post-translational insertion route into the ER membrane. In this review, we summarize the current research in TA protein insertion with a special focus on plants, address challenges, and highlight future research avenues.
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Affiliation(s)
- Dietmar G Mehlhorn
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
| | - Lisa Y Asseck
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
| | - Christopher Grefen
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
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6
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Kumar T, Maitra S, Rahman A, Bhattacharjee S. A conserved guided entry of tail-anchored pathway is involved in the trafficking of a subset of membrane proteins in Plasmodium falciparum. PLoS Pathog 2021; 17:e1009595. [PMID: 34780541 PMCID: PMC8629386 DOI: 10.1371/journal.ppat.1009595] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 11/29/2021] [Accepted: 10/19/2021] [Indexed: 01/22/2023] Open
Abstract
Tail-anchored (TA) proteins are defined by the absence of N-terminus signal sequence and the presence of a single transmembrane domain (TMD) proximal to their C-terminus. They play fundamental roles in cellular processes including vesicular trafficking, protein translocation and quality control. Some of the TA proteins are post-translationally integrated by the Guided Entry of TA (GET) pathway to the cellular membranes; with their N-terminus oriented towards the cytosol and C-terminus facing the organellar lumen. The TA repertoire and the GET machinery have been extensively characterized in the yeast and mammalian systems, however, they remain elusive in the human malaria parasite Plasmodium falciparum. In this study, we bioinformatically predicted a total of 63 TA proteins in the P. falciparum proteome and revealed the association of a subset with the P. falciparum homolog of Get3 (PfGet3). In addition, our proximity labelling studies either definitively identified or shortlisted the other eligible GET constituents, and our in vitro association studies validated associations between PfGet3 and the corresponding homologs of Get4 and Get2 in P. falciparum. Collectively, this study reveals the presence of proteins with hallmark TA signatures and the involvement of evolutionary conserved GET trafficking pathway for their targeted delivery within the parasite. Tail-anchored (TA) membrane proteins are known to play essential cellular functions in the eukaryotes. These proteins are trafficked to their respective destinations by post-translational translocation pathways that are evolutionarily conserved from yeast to human. However, they remain unidentified in the malaria parasite Plasmodium falciparum. We have used bioinformatic prediction algorithms in conjunction with functional validation studies to identify the candidate TA repertoire and some of the homologs of the trafficking machinery in P. falciparum. Initially, we predicted the presence of 63 putative TA proteins localized to distinct compartments within this parasite, including a few confirmed TA homologs in other eukaryotic systems. We then identified and characterized PfGet3 as a central component in the Guided-Entry of TA (GET) translocation machinery, and our bacterial co-expression and pulldown assays with two selected recombinant TA proteins, PfBOS1 and PfUSE1, showed co-association with PfGet3. We also identified PfGet2 and PfGet4 as the other two components of the GET machinery in P. falciparum using proximity biotinylation followed by mass spectrometry. Interestingly, we also found six TA proteins in the parasite enriched in this fraction. We further validated the direct interactions between a few TA candidates, PfGet4 and PfGet2 with PfGet3 using recombinant-based pulldown studies. In conclusion, this study classified a subset of membrane proteins with the TA nomenclature and implicated a previously unidentified GET pathway for their translocation in this apicomplexan parasite.
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Affiliation(s)
- Tarkeshwar Kumar
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
| | - Satarupa Maitra
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
| | - Abdur Rahman
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
| | - Souvik Bhattacharjee
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
- * E-mail:
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7
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Zhang R, Guan X, Yang M, Law YS, Voon CP, Yan J, Sun F, Lim BL. Overlapping Functions of the Paralogous Proteins AtPAP2 and AtPAP9 in Arabidopsis thaliana. Int J Mol Sci 2021; 22:7243. [PMID: 34298863 PMCID: PMC8303434 DOI: 10.3390/ijms22147243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Revised: 06/29/2021] [Accepted: 07/01/2021] [Indexed: 11/16/2022] Open
Abstract
Arabidopsis thaliana purple acid phosphatase 2 (AtPAP2), which is anchored to the outer membranes of chloroplasts and mitochondria, affects carbon metabolism by modulating the import of some preproteins into chloroplasts and mitochondria. AtPAP9 bears a 72% amino acid sequence identity with AtPAP2, and both proteins carry a hydrophobic motif at their C-termini. Here, we show that AtPAP9 is a tail-anchored protein targeted to the outer membrane of chloroplasts. Yeast two-hybrid and bimolecular fluorescence complementation experiments demonstrated that both AtPAP9 and AtPAP2 bind to a small subunit of rubisco 1B (AtSSU1B) and a number of chloroplast proteins. Chloroplast import assays using [35S]-labeled AtSSU1B showed that like AtPAP2, AtPAP9 also plays a role in AtSSU1B import into chloroplasts. Based on these data, we propose that AtPAP9 and AtPAP2 perform overlapping roles in modulating the import of specific proteins into chloroplasts. Most plant genomes contain only one PAP-like sequence encoding a protein with a hydrophobic motif at the C-terminus. The presence of both AtPAP2 and AtPAP9 in the Arabidopsis genome may have arisen from genome duplication in Brassicaceae. Unlike AtPAP2 overexpression lines, the AtPAP9 overexpression lines did not exhibit early-bolting or high-seed-yield phenotypes. Their differential growth phenotypes could be due to the inability of AtPAP9 to be targeted to mitochondria, as the overexpression of AtPAP2 on mitochondria enhances the capacity of mitochondria to consume reducing equivalents.
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Affiliation(s)
- Renshan Zhang
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
| | - Xiaoqian Guan
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
| | - Meijing Yang
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
| | - Yee-Song Law
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
| | - Chia Pao Voon
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
| | - Junran Yan
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
| | - Feng Sun
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
| | - Boon Leong Lim
- School of Biological Sciences, The University of Hong Kong, Hong Kong, China; (R.Z.); (X.G.); (M.Y.); (Y.-S.L.); (C.P.V.); (J.Y.); (F.S.)
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China
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8
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Xu Z, Zhang R, Yang M, Law YS, Sun F, Hon NL, Ngai SM, Lim BL. A Balance between the Activities of Chloroplasts and Mitochondria Is Crucial for Optimal Plant Growth. Antioxidants (Basel) 2021; 10:935. [PMID: 34207819 PMCID: PMC8228383 DOI: 10.3390/antiox10060935] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 05/31/2021] [Accepted: 06/04/2021] [Indexed: 01/16/2023] Open
Abstract
Energy metabolism in plant cells requires a balance between the activities of chloroplasts and mitochondria, as they are the producers and consumers of carbohydrates and reducing equivalents, respectively. Recently, we showed that the overexpression of Arabidopsis thaliana purple acid phosphatase 2 (AtPAP2), a phosphatase dually anchored on the outer membranes of chloroplasts and mitochondria, can boost the plant growth and seed yield of Arabidopsis thaliana by coordinating the activities of both organelles. However, when AtPAP2 is solely overexpressed in chloroplasts, the growth-promoting effects are less optimal, indicating that active mitochondria are required for dissipating excess reducing equivalents from chloroplasts to maintain the optimal growth of plants. It is even more detrimental to plant productivity when AtPAP2 is solely overexpressed in mitochondria. Although these lines contain high level of adenosine triphosphate (ATP), they exhibit low leaf sucrose, low seed yield, and early senescence. These transgenic lines can be useful tools for studying how hyperactive chloroplasts or mitochondria affect the physiology of their counterparts and how they modify cellular metabolism and plant physiology.
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Affiliation(s)
- Zhou Xu
- School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China; (Z.X.); (R.Z.); (M.Y.); (Y.-S.L.); (F.S.)
| | - Renshan Zhang
- School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China; (Z.X.); (R.Z.); (M.Y.); (Y.-S.L.); (F.S.)
| | - Meijing Yang
- School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China; (Z.X.); (R.Z.); (M.Y.); (Y.-S.L.); (F.S.)
| | - Yee-Song Law
- School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China; (Z.X.); (R.Z.); (M.Y.); (Y.-S.L.); (F.S.)
| | - Feng Sun
- School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China; (Z.X.); (R.Z.); (M.Y.); (Y.-S.L.); (F.S.)
| | - Ngai Lung Hon
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China; (N.L.H.); (S.M.N.)
| | - Sai Ming Ngai
- School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China; (N.L.H.); (S.M.N.)
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong, China
| | - Boon Leong Lim
- School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China; (Z.X.); (R.Z.); (M.Y.); (Y.-S.L.); (F.S.)
- State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong, China
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Wojcik S, Kriechbaumer V. Go your own way: membrane-targeting sequences. PLANT PHYSIOLOGY 2021; 185:608-618. [PMID: 33822216 PMCID: PMC8133554 DOI: 10.1093/plphys/kiaa058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 10/19/2020] [Indexed: 05/05/2023]
Abstract
Membrane-targeting sequences, connected targeting mechanisms, and co-factors orchestrate primary targeting of proteins to membranes.
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Affiliation(s)
- Stefan Wojcik
- Plant Cell Biology, Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, UK
| | - Verena Kriechbaumer
- Plant Cell Biology, Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, UK
- Author for communication: (V.K.)
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10
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Price AM, Doner NM, Gidda SK, Jambunathan S, James CN, Schami A, Yurchenko O, Mullen RT, Dyer JM, Puri V, Chapman KD. Mouse Fat-Specific Protein 27 (FSP27) expressed in plant cells localizes to lipid droplets and promotes lipid droplet accumulation and fusion. Biochimie 2020; 169:41-53. [PMID: 31400447 DOI: 10.1016/j.biochi.2019.08.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Accepted: 08/05/2019] [Indexed: 10/26/2022]
Abstract
Fat-Specific Protein 27 (FSP27) belongs to a small group of vertebrate proteins containing a Cell-death Inducing DNA fragmentation factor-α-like Effector (CIDE)-C domain and is involved in lipid droplet (LD) accumulation and energy homeostasis. FSP27 is predominantly expressed in white and brown adipose tissues, as well as liver, and plays a key role in mediating LD-LD fusion. No orthologs have been identified in invertebrates or plants. In this study, we tested the function of mouse FSP27 in stably-transformed Arabidopsis thaliana leaves and seeds, as well as through transient expression in Nicotiana tabacum suspension-cultured cells and N. benthamiana leaves. Confocal microscopic analysis of plant cells revealed that, similar to ectopic expression in mammalian cells, FSP27 produced in plants 1) correctly localized to LDs, 2) accumulated at LD-LD contact sites, and 3) induced an increase in the number and size of LDs and also promoted LD clustering and fusion. Furthermore, FSP27 increased oil content in transgenic A. thaliana seeds. Given that plant oils have uses in human and animal nutrition as well as industrial uses such as biofuels and bioplastics, our results suggest that ectopic expression of FSP27 in plants represents a potential strategy for increasing oil content and energy density in bioenergy or oilseed crops.
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Affiliation(s)
- Ann M Price
- BioDiscovery Institute, Department of Biological Sciences, University of North Texas, Denton, TX, USA
| | - Nathan M Doner
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Satinder K Gidda
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Srikarthika Jambunathan
- Department of Medicine, Section of Endocrinology, Diabetes and Nutrition, Boston University School of Medicine, Boston, MA, USA
| | - Christopher N James
- BioDiscovery Institute, Department of Biological Sciences, University of North Texas, Denton, TX, USA
| | - Alyssa Schami
- BioDiscovery Institute, Department of Biological Sciences, University of North Texas, Denton, TX, USA
| | - Olga Yurchenko
- USDA-ARS, US Arid-Land Agricultural Research Center, Maricopa, AZ, USA
| | - Robert T Mullen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - John M Dyer
- USDA-ARS, US Arid-Land Agricultural Research Center, Maricopa, AZ, USA
| | - Vishwajeet Puri
- Department of Biomedical Sciences and the Diabetes Institute, Ohio University, Athens, OH, USA
| | - Kent D Chapman
- BioDiscovery Institute, Department of Biological Sciences, University of North Texas, Denton, TX, USA.
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11
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Brito GC, Schormann W, Gidda SK, Mullen RT, Andrews DW. Genome-wide analysis of Homo sapiens, Arabidopsis thaliana, and Saccharomyces cerevisiae reveals novel attributes of tail-anchored membrane proteins. BMC Genomics 2019; 20:835. [PMID: 31711414 PMCID: PMC6849228 DOI: 10.1186/s12864-019-6232-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Accepted: 10/28/2019] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND Tail-anchored membrane proteins (TAMPs) differ from other integral membrane proteins, because they contain a single transmembrane domain at the extreme carboxyl-terminus and are therefore obliged to target to membranes post-translationally. Although 3-5% of all transmembrane proteins are predicted to be TAMPs only a small number are well characterized. RESULTS To identify novel putative TAMPs across different species, we used TAMPfinder software to identify 859, 657 and 119 putative TAMPs in human (Homo sapiens), plant (Arabidopsis thaliana), and yeast (Saccharomyces cerevisiae), respectively. Bioinformatics analyses of these putative TAMP sequences suggest that the list is highly enriched for authentic TAMPs. To experimentally validate the software predictions several human and plant proteins identified by TAMPfinder that were previously uncharacterized were expressed in cells and visualized at subcellular membranes by fluorescence microscopy and further analyzed by carbonate extraction or by bimolecular fluorescence complementation. With the exception of the pro-apoptotic protein harakiri, which is, peripherally bound to the membrane this subset of novel proteins behave like genuine TAMPs. Comprehensive bioinformatics analysis of the generated TAMP datasets revealed previously unappreciated common and species-specific features such as the unusual size distribution of and the propensity of TAMP proteins to be part of larger complexes. Additionally, novel features of the amino acid sequences that anchor TAMPs to membranes were also revealed. CONCLUSIONS The findings in this study more than double the number of predicted annotated TAMPs and provide new insights into the common and species-specific features of TAMPs. Furthermore, the list of TAMPs and annotations provide a resource for further investigation.
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Affiliation(s)
- Glauber Costa Brito
- Biological Sciences, Sunnybrook Research Institute, Toronto, ON, M4N 3M5, Canada
| | - Wiebke Schormann
- Biological Sciences, Sunnybrook Research Institute, Toronto, ON, M4N 3M5, Canada
| | - Satinder K Gidda
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada
| | - Robert T Mullen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada
| | - David W Andrews
- Biological Sciences, Sunnybrook Research Institute, Toronto, ON, M4N 3M5, Canada. .,Departments of Biochemistry and Medical Biophysics, University of Toronto, Toronto, ON, Canada.
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12
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Lin TW, Chen CC, Wu SM, Chang YC, Li YC, Su YW, Hsiao CD, Chang HY. Structural analysis of chloroplast tail-anchored membrane protein recognition by ArsA1. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2019; 99:128-143. [PMID: 30891827 DOI: 10.1111/tpj.14316] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Revised: 02/26/2019] [Accepted: 03/11/2019] [Indexed: 06/09/2023]
Abstract
In mammals and yeast, tail-anchored (TA) membrane proteins destined for the post-translational pathway are safely delivered to the endoplasmic reticulum (ER) membrane by a well-known targeting factor, TRC40/Get3. In contrast, the underlying mechanism for translocation of TA proteins in plants remains obscure. How this unique eukaryotic membrane-trafficking system correctly distinguishes different subsets of TA proteins destined for various organelles, including mitochondria, chloroplasts and the ER, is a key question of long standing. Here, we present crystal structures of algal ArsA1 (the Get3 homolog) in a distinct nucleotide-free open state and bound to adenylyl-imidodiphosphate. This approximately 80-kDa protein possesses a monomeric architecture, with two ATPase domains in a single polypeptide chain. It is capable of binding chloroplast (TOC34 and TOC159) and mitochondrial (TOM7) TA proteins based on features of its transmembrane domain as well as the regions immediately before and after the transmembrane domain. Several helices located above the TA-binding groove comprise the interlocking hook-like motif implicated by mutational analyses in TA substrate recognition. Our data provide insights into the molecular basis of the highly specific selectivity of interactions of algal ArsA1 with the correct sets of TA substrates before membrane targeting in plant cells.
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Affiliation(s)
- Tai-Wen Lin
- Molecular and Cell Biology, International Graduate Program, Academia Sinica and Graduate Institute of Life Science, National Defense Medical Center, Taipei, Taiwan
- Institute of Molecular Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, 11529, Taiwan
| | - Chi-Chih Chen
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
- The Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
- Doctoral Degree Program in Marine Biotechnology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, 11529, Taiwan
- Doctoral Degree Program in Marine Biotechnology, National Sun Yat-Sen University, 70 Lien-Hai Road, Kaohsiung, 80424, Taiwan
| | - Shu-Mei Wu
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
| | - Yu-Ching Chang
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
| | - Yi-Chuan Li
- Molecular and Cell Biology, International Graduate Program, Academia Sinica and Graduate Institute of Life Science, National Defense Medical Center, Taipei, Taiwan
| | - Yu-Wang Su
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
| | - Chwan-Deng Hsiao
- Molecular and Cell Biology, International Graduate Program, Academia Sinica and Graduate Institute of Life Science, National Defense Medical Center, Taipei, Taiwan
- Institute of Molecular Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, 11529, Taiwan
- Doctoral Degree Program in Marine Biotechnology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei, 11529, Taiwan
| | - Hsin-Yang Chang
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
- The Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
- Doctoral Degree Program in Marine Biotechnology, National Sun Yat-Sen University, 70 Lien-Hai Road, Kaohsiung, 80424, Taiwan
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13
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Kim J, Na YJ, Park SJ, Baek SH, Kim DH. Biogenesis of chloroplast outer envelope membrane proteins. PLANT CELL REPORTS 2019; 38:783-792. [PMID: 30671649 DOI: 10.1007/s00299-019-02381-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Accepted: 01/11/2019] [Indexed: 06/09/2023]
Abstract
Most organisms on Earth use glucose, a photosynthetic product, as energy source. The chloroplast, the home of photosynthesis, is the most representative and characteristic organelle in plants and is enclosed by the outer envelope and inner envelope membranes. The chloroplast biogenesis and unique functions are very closely associated with proteins in the two envelope membranes of the chloroplast. Especially, the chloroplast outer envelope membrane proteins have important roles in signal transduction, protein import, lipid biosynthesis and remodeling, exchange of ions and numerous metabolites, plastid division, movement, and host defense. Therefore, biogenesis of these membrane proteins of chloroplast outer envelope membrane is very important for biogenesis of the entire chloroplast proteome as well as plant development. Most proteins among the outer envelope membrane proteins are encoded by the nuclear genome and are post-translationally targeted to the chloroplast outer envelope membrane. In this process, cytoplasmic receptor and import machineries are required for efficient and correct targeting of these membrane proteins. In this review, we have summarized recent advances on the sorting, targeting, and insertion mechanisms of the outer envelope membrane proteins of chloroplasts and also provide future direction of the study on these topics.
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Affiliation(s)
- Jonghak Kim
- Department of Biology, Sunchon National University, Sunchon, 57922, South Korea
| | - Yun Jeong Na
- Department of Biology, Sunchon National University, Sunchon, 57922, South Korea
| | - Soon Ju Park
- Biological Sciences and Research Institute for Basic Science, Wonkwang University, Iksan, 54538, South Korea
| | - So-Hyeon Baek
- Department of Well-being Resources, Sunchon National University, Sunchon, 57922, South Korea
| | - Dae Heon Kim
- Department of Biology, Sunchon National University, Sunchon, 57922, South Korea.
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14
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Moog D. Higher Complexity Requires Higher Accuracy: Tail-Anchored Protein Targeting to the Outer Envelope Membrane of Plant Plastids via a Specific C-Terminal Motif. PLANT & CELL PHYSIOLOGY 2019; 60:489-491. [PMID: 30715537 DOI: 10.1093/pcp/pcz021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 01/22/2019] [Indexed: 06/09/2023]
Affiliation(s)
- Daniel Moog
- Laboratory for Cell Biology, Faculty of Biology, Philipps University Marburg, Karl-von-Frisch-Str. 8, Marburg, Germany
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15
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Teresinski HJ, Gidda SK, Nguyen TND, Howard NJM, Porter BK, Grimberg N, Smith MD, Andrews DW, Dyer JM, Mullen RT. An RK/ST C-Terminal Motif is Required for Targeting of OEP7.2 and a Subset of Other Arabidopsis Tail-Anchored Proteins to the Plastid Outer Envelope Membrane. PLANT & CELL PHYSIOLOGY 2019; 60:516-537. [PMID: 30521026 DOI: 10.1093/pcp/pcy234] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Accepted: 12/03/2018] [Indexed: 06/09/2023]
Abstract
Tail-anchored (TA) proteins are a unique class of integral membrane proteins that possess a single C-terminal transmembrane domain and target post-translationally to the specific organelles at which they function. While significant advances have been made in recent years in elucidating the mechanisms and molecular targeting signals involved in the proper sorting of TA proteins, particularly to the endoplasmic reticulum and mitochondria, relatively little is known about the targeting of TA proteins to the plastid outer envelope. Here we show that several known or predicted plastid TA outer envelope proteins (OEPs) in Arabidopsis possess a C-terminal RK/ST sequence motif that serves as a conserved element of their plastid targeting signal. Evidence for this conclusion comes primarily from experiments with OEP7.2, which is a member of the Arabidopsis 7 kDa OEP family. We confirmed that OEP7.2 is localized to the plastid outer envelope and possesses a TA topology, and its C-terminal sequence (CTS), which includes the RK/ST motif, is essential for proper targeting to plastids. The CTS of OEP7.2 is functionally interchangeable with the CTSs of other TA OEPs that possess similar RK/ST motifs, but not with those that lack the motif. Further, a bioinformatics search based on a consensus sequence led to the identification of several new OEP TA proteins. Collectively, this study provides new insight into the mechanisms of TA protein sorting in plant cells, defines a new targeting signal element for a subset of TA OEPs and expands the number and repertoire of TA proteins at the plastid outer envelope.
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Affiliation(s)
- Howard J Teresinski
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Satinder K Gidda
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Thuy N D Nguyen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Naomi J Marty Howard
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Brittany K Porter
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada
| | - Nicholas Grimberg
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada
| | - Matthew D Smith
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada
| | - David W Andrews
- Sunnybrook Research Institute and Departments of Biochemistry and Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - John M Dyer
- United States Department of Agriculture, Agricultural Research Service, US Arid-Land Agricultural Research Center, Maricopa, USA
| | - Robert T Mullen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
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16
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Day PM, Theg SM. Evolution of protein transport to the chloroplast envelope membranes. PHOTOSYNTHESIS RESEARCH 2018; 138:315-326. [PMID: 30291507 DOI: 10.1007/s11120-018-0540-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Accepted: 06/20/2018] [Indexed: 05/11/2023]
Abstract
Chloroplasts are descendants of an ancient endosymbiotic cyanobacterium that lived inside a eukaryotic cell. They inherited the prokaryotic double membrane envelope from cyanobacteria. This envelope contains prokaryotic protein sorting machineries including a Sec translocase and relatives of the central component of the bacterial outer membrane β-barrel assembly module. As the endosymbiont was integrated with the rest of the cell, the synthesis of most of its proteins shifted from the stroma to the host cytosol. This included nearly all the envelope proteins identified so far. Consequently, the overall biogenesis of the chloroplast envelope must be distinct from cyanobacteria. Envelope proteins initially approach their functional locations from the exterior rather than the interior. In many cases, they have been shown to use components of the general import pathway that also serves the stroma and thylakoids. If the ancient prokaryotic protein sorting machineries are still used for chloroplast envelope proteins, their activities must have been modified or combined with the general import pathway. In this review, we analyze the current knowledge pertaining to chloroplast envelope biogenesis and compare this to bacteria.
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Affiliation(s)
- Philip M Day
- Department of Plant Biology, University of California at Davis, 1 Shields Avenue, Davis, CA, USA
| | - Steven M Theg
- Department of Plant Biology, University of California at Davis, 1 Shields Avenue, Davis, CA, USA.
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17
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Aznar-Moreno JA, Sánchez R, Gidda SK, Martínez-Force E, Moreno-Pérez AJ, Venegas Calerón M, Garcés R, Mullen RT, Salas JJ. New Insights Into Sunflower ( Helianthus annuus L.) FatA and FatB Thioesterases, Their Regulation, Structure and Distribution. FRONTIERS IN PLANT SCIENCE 2018; 9:1496. [PMID: 30459777 PMCID: PMC6232763 DOI: 10.3389/fpls.2018.01496] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 09/25/2018] [Indexed: 05/13/2023]
Abstract
Sunflower seeds (Helianthus annuus L.) accumulate large quantities of triacylglycerols (TAG) between 12 and 28 days after flowering (DAF). This is the period of maximal acyl-acyl carrier protein (acyl-ACP) thioesterase activity in vitro, the enzymes that terminate the process of de novo fatty acid synthesis by catalyzing the hydrolysis of the acyl-ACPs synthesized by fatty acid synthase. Fatty acid thioesterases can be classified into two families with distinct substrate specificities, namely FatA and FatB. Here, some new aspects of these enzymes have been studied, assessing how both enzymes contribute to the acyl composition of sunflower oil, not least through the changes in their expression during the process of seed filling. Moreover, the binding pockets of these enzymes were modeled based on new data from plant thioesterases, revealing important differences in their volume and geometry. Finally, the subcellular location of the two enzymes was evaluated and while both possess an N-terminal plastid transit peptide, only in FatB contains a hydrophobic sequence that could potentially serve as a transmembrane domain. Indeed, using in vivo imaging and organelle fractionation, H. annuus thioesterases, HaFatA and HaFatB, appear to be differentially localized in the plastid stroma and membrane envelope, respectively. The divergent roles fulfilled by HaFatA and HaFatB in oil biosynthesis are discussed in the light of our data.
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Affiliation(s)
- Jose A. Aznar-Moreno
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS, United States
| | - Rosario Sánchez
- Instituto de la Grasa (CSIC), Campus Universitario Pablo de Olavide, Seville, Spain
| | - Satinder K. Gidda
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | | | | | - Mónica Venegas Calerón
- Instituto de la Grasa (CSIC), Campus Universitario Pablo de Olavide, Seville, Spain
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Seville, Spain
| | - Rafael Garcés
- Instituto de la Grasa (CSIC), Campus Universitario Pablo de Olavide, Seville, Spain
| | - Robert T. Mullen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Joaquín J. Salas
- Instituto de la Grasa (CSIC), Campus Universitario Pablo de Olavide, Seville, Spain
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18
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Abstract
Proper localization of membrane proteins is essential for the function of biological membranes and for the establishment of organelle identity within a cell. Molecular machineries that mediate membrane protein biogenesis need to not only achieve a high degree of efficiency and accuracy, but also prevent off-pathway aggregation events that can be detrimental to cells. The posttranslational targeting of tail-anchored proteins (TAs) provides tractable model systems to probe these fundamental issues. Recent advances in understanding TA-targeting pathways reveal sophisticated molecular machineries that drive and regulate these processes. These findings also suggest how an interconnected network of targeting factors, cochaperones, and quality control machineries together ensures robust membrane protein biogenesis.
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Affiliation(s)
- Un Seng Chio
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125; , ,
| | - Hyunju Cho
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125; , ,
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125; , ,
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19
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A plastidial pantoate transporter with a potential role in pantothenate synthesis. Biochem J 2018; 475:813-825. [DOI: 10.1042/bcj20170883] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Revised: 01/26/2018] [Accepted: 01/30/2018] [Indexed: 11/17/2022]
Abstract
The pantothenate (vitamin B5) synthesis pathway in plants is not fully defined because the subcellular site of its ketopantoate → pantoate reduction step is unclear. However, the pathway is known to be split between cytosol, mitochondria, and potentially plastids, and inferred to involve mitochondrial or plastidial transport of ketopantoate or pantoate. No proteins that mediate these transport steps have been identified. Comparative genomic and transcriptomic analyses identified Arabidopsis thaliana BASS1 (At1g78560) and its maize (Zea mays) ortholog as candidates for such a transport role. BASS1 proteins belong to the bile acid : sodium symporter family and share similarity with the Salmonella enterica PanS pantoate/ketopantoate transporter and with predicted bacterial transporters whose genes cluster on the chromosome with pantothenate synthesis genes. Furthermore, Arabidopsis BASS1 is co-expressed with genes related to metabolism of coenzyme A, the cofactor derived from pantothenate. Expression of Arabidopsis or maize BASS1 promoted the growth of a S. enterica panB panS mutant strain when pantoate, but not ketopantoate, was supplied, and increased the rate of [3H]pantoate uptake. Subcellular localization of green fluorescent protein fusions in Nicotiana tabacum BY-2 cells demonstrated that Arabidopsis BASS1 is targeted solely to the plastid inner envelope. Two independent Arabidopsis BASS1 knockout mutants accumulated pantoate ∼10-fold in leaves and had smaller seeds. Taken together, these data indicate that BASS1 is a physiologically significant plastidial pantoate transporter and that the pantoate reduction step in pantothenate biosynthesis could be at least partly localized in plastids.
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20
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Barton KA, Wozny MR, Mathur N, Jaipargas EA, Mathur J. Chloroplast behaviour and interactions with other organelles in Arabidopsis thaliana pavement cells. J Cell Sci 2018; 131:jcs.202275. [PMID: 28320821 DOI: 10.1242/jcs.202275] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Accepted: 03/16/2017] [Indexed: 01/11/2023] Open
Abstract
Chloroplasts are a characteristic feature of green plants. Mesophyll cells possess the majority of chloroplasts and it is widely believed that, with the exception of guard cells, the epidermal layer in most higher plants does not contain chloroplasts. However, recent observations on Arabidopsis thaliana have shown a population of chloroplasts in pavement cells that are smaller than mesophyll chloroplasts and have a high stroma to grana ratio. Here, using stable transgenic lines expressing fluorescent proteins targeted to the plastid stroma, plasma membrane, endoplasmic reticulum, tonoplast, nucleus, mitochondria, peroxisomes, F-actin and microtubules, we characterize the spatiotemporal relationships between the pavement cell chloroplasts (PCCs) and their subcellular environment. Observations on the PCCs suggest a source-sink relationship between the epidermal and the mesophyll layers, and experiments with the Arabidopsis mutants glabra2 (gl2) and immutans (im), which show altered epidermal plastid development, underscored their developmental plasticity. Our findings lay down the foundation for further investigations aimed at understanding the precise role and contributions of PCCs in plant interactions with the environment.
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Affiliation(s)
- Kiah A Barton
- Laboratory of Plant Development and Interactions, Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Road, Guelph, Ontario N1G2W1, Canada
| | - Michael R Wozny
- Laboratory of Plant Development and Interactions, Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Road, Guelph, Ontario N1G2W1, Canada
| | - Neeta Mathur
- Laboratory of Plant Development and Interactions, Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Road, Guelph, Ontario N1G2W1, Canada
| | - Erica-Ashley Jaipargas
- Laboratory of Plant Development and Interactions, Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Road, Guelph, Ontario N1G2W1, Canada
| | - Jaideep Mathur
- Laboratory of Plant Development and Interactions, Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Road, Guelph, Ontario N1G2W1, Canada
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21
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Lee DW, Lee J, Hwang I. Sorting of nuclear-encoded chloroplast membrane proteins. CURRENT OPINION IN PLANT BIOLOGY 2017; 40:1-7. [PMID: 28668581 DOI: 10.1016/j.pbi.2017.06.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Revised: 06/07/2017] [Accepted: 06/14/2017] [Indexed: 05/11/2023]
Abstract
Among the many organelles in eukaryotic cells, chloroplasts have the most complex structure, with multiple suborganellar membranes, making protein targeting to chloroplasts, particularly to various suborganellar membranes, highly challenging. Multiple mechanisms function in the biogenesis of chloroplast membrane proteins. Nuclear-encoded nascent proteins can be targeted to the outer envelope membrane directly from the cytosol after translation, but their targeting to the inner envelope and thylakoid membranes requires multiple steps, including cytosolic sorting, translocation across the envelope membranes, sorting in the stroma, and insertion into their target membranes. In this review, we discuss the current knowledge about the sorting mechanisms of proteins to the two envelope membranes and the thylakoid membrane, along with perspectives for future research.
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Affiliation(s)
- Dong Wook Lee
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Junho Lee
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Inhwan Hwang
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 37673, Republic of Korea; Department of Life Sciences, Pohang University of Science and Technology, Pohang 37673, Republic of Korea.
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22
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Islam Z, Nagampalli RSK, Fatima MT, Ashraf GM. New paradigm in ankyrin repeats: Beyond protein-protein interaction module. Int J Biol Macromol 2017; 109:1164-1173. [PMID: 29157912 DOI: 10.1016/j.ijbiomac.2017.11.101] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2017] [Revised: 11/13/2017] [Accepted: 11/16/2017] [Indexed: 01/06/2023]
Abstract
Classically, ankyrin repeat (ANK) proteins are built from tandems of two or more repeats and form curved solenoid structures that are associated with protein-protein interactions. These are short, widespread structural motif of around 33 amino acids repeats in tandem, having a canonical helix-loop-helix fold, found individually or in combination with other domains. The multiplicity of structural pattern enables it to form assemblies of diverse sizes, required for their abilities to confer multiple binding and structural roles of proteins. Three-dimensional structures of these repeats determined to date reveal a degree of structural variability that translates into the considerable functional versatility of this protein superfamily. Recent work on the ANK has proposed novel structural information, especially protein-lipid, protein-sugar and protein-protein interaction. Self-assembly of these repeats was also shown to prevent the associated protein in forming filaments. In this review, we summarize the latest findings and how the new structural information has increased our understanding of the structural determinants of ANK proteins. We discussed latest findings on how these proteins participate in various interactions to diversify the ANK roles in numerous biological processes, and explored the emerging and evolving field of designer ankyrins and its framework for protein engineering emphasizing on biotechnological applications.
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Affiliation(s)
- Zeyaul Islam
- Laboratório Nacional de Biociências, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, SP, 13083-100, Brazil.
| | | | - Munazza Tamkeen Fatima
- Department of Biochemistry and Tissue Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, SP, 13083-862, Brazil
| | - Ghulam Md Ashraf
- King Fahd Medical Research Center, King Abdulaziz University, P.O. Box 80216, Jeddah, 21589, Saudi Arabia.
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23
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Maestre-Reyna M, Wu SM, Chang YC, Chen CC, Maestre-Reyna A, Wang AHJ, Chang HY. In search of tail-anchored protein machinery in plants: reevaluating the role of arsenite transporters. Sci Rep 2017; 7:46022. [PMID: 28382961 PMCID: PMC5382584 DOI: 10.1038/srep46022] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 03/07/2017] [Indexed: 11/09/2022] Open
Abstract
Although the mechanisms underlying selective targeting of tail-anchored (TA) membrane proteins are well established in mammalian and yeast cells, little is known about their role in mediating intracellular membrane trafficking in plant cells. However, a recent study suggested that, in green algae, arsenite transporters located in the cytosol (ArsA1 and ArsA2) control the insertion of TA proteins into the membrane-bound organelles. In the present work, we overproduced and purified these hydrophilic proteins to near homogeneity. The analysis of their catalytic properties clearly demonstrates that C. reinhardtii ArsA proteins exhibit oxyanion-independent ATPase activity, as neither arsenite nor antimonite showed strong effects. Co-expression of ArsA proteins with TA-transmembrane regions showed not only that the former interact with the latter, but that ArsA1 does not share the same ligand specificity as ArsA2. Together with a structural model and molecular dynamics simulations, we propose that C. reinhadtii ArsA proteins are not arsenite transporters, but a TA-protein targeting factor. Further, we propose that ArsA targeting specificity is achieved at the ligand level, with ArsA1 mainly carrying TA-proteins to the chloroplast, while ArsA2 to the endoplasmic reticulum.
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Affiliation(s)
| | - Shu-Mei Wu
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, Taiwan
| | - Yu-Ching Chang
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, Taiwan
| | - Chi-Chih Chen
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, Taiwan
- Doctoral Degree Program in Marine Biotechnology, National Sun Yat-Sen University, 70 Lien-Hai Road, Kaohsiung 80424, Taiwan
- Doctoral Degree Program in Marine Biotechnology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan
| | - Alvaro Maestre-Reyna
- Escuela Tecnica Superior de Ingenierios Industriales, Universidad Politecnica de Valencia, Valencia, Spain
| | - Andrew H.-J. Wang
- Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
- Core Facilities for Protein Structural Analysis, Academia Sinica, Taipei, Taiwan
- PhD Program for Translational Medicine, College of Medical Science and Technology, Taipei Medical University, Taipei, Taiwan
| | - Hsin-Yang Chang
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, Taiwan
- Doctoral Degree Program in Marine Biotechnology, National Sun Yat-Sen University, 70 Lien-Hai Road, Kaohsiung 80424, Taiwan
- The Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 804, Taiwan
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24
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Zufferey M, Montandon C, Douet V, Demarsy E, Agne B, Baginsky S, Kessler F. The novel chloroplast outer membrane kinase KOC1 is a required component of the plastid protein import machinery. J Biol Chem 2017; 292:6952-6964. [PMID: 28283569 DOI: 10.1074/jbc.m117.776468] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Revised: 02/28/2017] [Indexed: 11/06/2022] Open
Abstract
The biogenesis and maintenance of cell organelles such as mitochondria and chloroplasts require the import of many proteins from the cytosol, a process that is controlled by phosphorylation. In the case of chloroplasts, the import of hundreds of different proteins depends on translocons at the outer and inner chloroplast membrane (TOC and TIC, respectively) complexes. The essential protein TOC159 functions thereby as an import receptor. It has an N-terminal acidic (A-) domain that extends into the cytosol, controls receptor specificity, and is highly phosphorylated in vivo However, kinases that phosphorylate the TOC159 A-domain to enable protein import have remained elusive. Here, using co-purification with TOC159 from Arabidopsis, we discovered a novel component of the chloroplast import machinery, the regulatory kinase at the outer chloroplast membrane 1 (KOC1). We found that KOC1 is an integral membrane protein facing the cytosol and stably associates with TOC. Moreover, KOC1 phosphorylated the A-domain of TOC159 in vitro, and in mutant koc1 chloroplasts, preprotein import efficiency was diminished. koc1 Arabidopsis seedlings had reduced survival rates after transfer from the dark to the light in which protein import into plastids is required to rapidly complete chloroplast biogenesis. In summary, our data indicate that KOC1 is a functional component of the TOC machinery that phosphorylates import receptors, supports preprotein import, and contributes to efficient chloroplast biogenesis.
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Affiliation(s)
- Mónica Zufferey
- From the Laboratory of Plant Physiology, University of Neuchâtel, 2000 Neuchâtel, Switzerland
| | - Cyrille Montandon
- the College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14853
| | - Véronique Douet
- From the Laboratory of Plant Physiology, University of Neuchâtel, 2000 Neuchâtel, Switzerland
| | - Emilie Demarsy
- the Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland, and
| | - Birgit Agne
- Institut für Biochemie und Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle (Saale), Germany
| | - Sacha Baginsky
- Institut für Biochemie und Biotechnologie, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle (Saale), Germany
| | - Felix Kessler
- From the Laboratory of Plant Physiology, University of Neuchâtel, 2000 Neuchâtel, Switzerland,
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Cho JH, Lee JH, Park YK, Choi MN, Kim KN. Calcineurin B-like Protein CBL10 Directly Interacts with TOC34 (Translocon of the Outer Membrane of the Chloroplasts) and Decreases Its GTPase Activity in Arabidopsis. FRONTIERS IN PLANT SCIENCE 2016; 7:1911. [PMID: 28018422 PMCID: PMC5156837 DOI: 10.3389/fpls.2016.01911] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Accepted: 12/02/2016] [Indexed: 05/27/2023]
Abstract
As calcium sensor relays in plants, calcineurin B-like (CBL) proteins provide an important contribution to decoding Ca2+ signatures elicited by a variety of abiotic stresses. Currently, it is well known that CBLs perceive and transmit the Ca2+ signals mainly to a group of serine/threonine protein kinases called CBL-interacting protein kinases (CIPKs). In this study, we report that the CBL10 member of this family has a novel interaction partner besides the CIPK proteins. Yeast two-hybrid screening with CBL10 as bait identified an Arabidopsis cDNA clone encoding a TOC34 protein, which is a member of the TOC (Translocon of the Outer membrane of the Chloroplasts) complex and possesses the GTPase activity. Further analyses showed that in addition to CBL10, CBL7 also interacts with TOC34 at much lower strength in the yeast two-hybrid system. However, the rest of the CBL family members failed to interact with TOC34. Bimolecular fluorescence complementation (BiFC) analysis verified that the CBL10-TOC34 interaction occurs at the outer membrane of chloroplasts in vivo. In addition, we also demonstrated that CBL10 physically associates with TOC34 in vitro, resulting in a significant decrease in the GTPase activity of the TOC34 protein. Taken together, our findings clearly indicate that a member of the CBL family, CBL10, can modulate not only the CIPK members but also TOC34, allowing the CBL family to relay the Ca2+ signals in more diverse ways than currently known.
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Affiliation(s)
| | | | | | | | - Kyung-Nam Kim
- Department of Molecular Biology, PERI, Sejong UniversitySeoul, South Korea
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Kim DH, Lee JE, Xu ZY, Geem KR, Kwon Y, Park JW, Hwang I. Cytosolic targeting factor AKR2A captures chloroplast outer membrane-localized client proteins at the ribosome during translation. Nat Commun 2015; 6:6843. [PMID: 25880450 DOI: 10.1038/ncomms7843] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Accepted: 03/04/2015] [Indexed: 01/30/2023] Open
Abstract
In eukaryotic cells, organellar proteome biogenesis is pivotal for cellular function. Chloroplasts contain a complex proteome, the biogenesis of which includes post-translational import of nuclear-encoded proteins. However, the mechanisms determining when and how nascent chloroplast-targeted proteins are sorted in the cytosol are unknown. Here, we establish the timing and mode of interaction between ankyrin repeat-containing protein 2 (AKR2A), the cytosolic targeting factor of chloroplast outer membrane (COM) proteins, and its interacting partners during translation at the single-molecule level. The targeting signal of a nascent AKR2A client protein residing in the ribosomal exit tunnel induces AKR2A binding to ribosomal RPL23A. Subsequently, RPL23A-bound AKR2A binds to the targeting signal when it becomes exposed from ribosomes. Failure of AKR2A binding to RPL23A in planta severely disrupts protein targeting to the COM; thus, AKR2A-mediated targeting of COM proteins is coupled to their translation, which in turn is crucial for biogenesis of the entire chloroplast proteome.
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Affiliation(s)
- Dae Heon Kim
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Jae-Eun Lee
- Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Zheng-Yi Xu
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Kyoung Rok Geem
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Yun Kwon
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Joon Won Park
- Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Inhwan Hwang
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.,Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea
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Lung SC, Smith MD, Weston JK, Gwynne W, Secord N, Chuong SDX. The C-terminus of Bienertia sinuspersici Toc159 contains essential elements for its targeting and anchorage to the chloroplast outer membrane. FRONTIERS IN PLANT SCIENCE 2014; 5:722. [PMID: 25566294 PMCID: PMC4274882 DOI: 10.3389/fpls.2014.00722] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2014] [Accepted: 11/30/2014] [Indexed: 05/11/2023]
Abstract
Most nucleus-encoded chloroplast proteins rely on an N-terminal transit peptide (TP) as a post-translational sorting signal for directing them to the organelle. Although Toc159 is known to be a receptor for specific preprotein TPs at the chloroplast surface, the mechanism for its own targeting and integration into the chloroplast outer membrane is not completely understood. In a previous study, we identified a novel TP-like sorting signal at the C-terminus (CT) of a Toc159 homolog from the single-cell C4 species, Bienertia sinuspersici. In the current study, we have extended our understanding of the sorting signal using transient expression of fluorescently-tagged fusion proteins of variable-length, and with truncated and swapped versions of the CT. As was shown in the earlier study, the 56 residues of the CT contain crucial sorting information for reversible interaction of the receptor with the chloroplast envelope. Extension of this region to 100 residues in the current study stabilized the interaction via membrane integration, as demonstrated by more prominent plastid-associated signals and resistance of the fusion protein to alkaline extraction. Despite a high degree of sequence similarity, the plastid localization signals of the equivalent CT regions of Arabidopsis thaliana Toc159 homologs were not as strong as that of the B. sinuspersici counterparts. Together with computational and circular dichroism analyses of the CT domain structures, our data provide insights into the critical elements of the CT for the efficient targeting and anchorage of Toc159 receptors to the dimorphic chloroplasts in the single-cell C4 species.
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Affiliation(s)
- Shiu-Cheung Lung
- School of Biological Sciences, The University of Hong KongHong Kong SAR, China
| | - Matthew D. Smith
- Department of Biology, Wilfrid Laurier UniversityWaterloo, ON, Canada
| | - J. Kyle Weston
- Department of Biology, Wilfrid Laurier UniversityWaterloo, ON, Canada
| | - William Gwynne
- Department of Biology, University of WaterlooWaterloo, ON, Canada
| | - Nathan Secord
- Department of Biology, University of WaterlooWaterloo, ON, Canada
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Kim DH, Park MJ, Gwon GH, Silkov A, Xu ZY, Yang EC, Song S, Song K, Kim Y, Yoon HS, Honig B, Cho W, Cho Y, Hwang I. An ankyrin repeat domain of AKR2 drives chloroplast targeting through coincident binding of two chloroplast lipids. Dev Cell 2014; 30:598-609. [PMID: 25203210 DOI: 10.1016/j.devcel.2014.07.026] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2013] [Revised: 05/22/2014] [Accepted: 07/31/2014] [Indexed: 10/24/2022]
Abstract
In organellogenesis of the chloroplast from endosymbiotic cyanobacteria, the establishment of protein-targeting mechanisms to the chloroplast should have been pivotal. However, it is still mysterious how these mechanisms were established and how they work in plant cells. Here we show that AKR2A, the cytosolic targeting factor for chloroplast outer membrane (COM) proteins, evolved from the ankyrin repeat domain (ARD) of the host cell by stepwise extensions of its N-terminal domain and that two lipids, monogalactosyldiacylglycerol (MGDG) and phosphatidylglycerol (PG), of the endosymbiont were selected to function as the AKR2A receptor. Structural analysis, molecular modeling, and mutational analysis of the ARD identified two adjacent sites for coincidental and synergistic binding of MGDG and PG. Based on these findings, we propose that the targeting mechanism of COM proteins was established using components from both the endosymbiont and host cell through a modification of the protein-protein-interacting ARD into a lipid binding domain.
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Affiliation(s)
- Dae Heon Kim
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Mi-Jeong Park
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Gwang Hyeon Gwon
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Antonina Silkov
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, NY 11032, USA
| | - Zheng-Yi Xu
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Eun Chan Yang
- Department of Biological Sciences, Sungkyunkwan University, Suwon 440-746, Korea
| | - Seohyeon Song
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Kyungyoung Song
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Younghyun Kim
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Hwan Su Yoon
- Department of Biological Sciences, Sungkyunkwan University, Suwon 440-746, Korea
| | - Barry Honig
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, NY 11032, USA
| | - Wonhwa Cho
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea; Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA.
| | - Yunje Cho
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
| | - Inhwan Hwang
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea; Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea.
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Paila YD, Richardson LGL, Schnell DJ. New insights into the mechanism of chloroplast protein import and its integration with protein quality control, organelle biogenesis and development. J Mol Biol 2014; 427:1038-1060. [PMID: 25174336 DOI: 10.1016/j.jmb.2014.08.016] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 08/20/2014] [Accepted: 08/23/2014] [Indexed: 01/04/2023]
Abstract
The translocons at the outer (TOC) and the inner (TIC) envelope membranes of chloroplasts mediate the targeting and import of several thousand nucleus-encoded preproteins that are required for organelle biogenesis and homeostasis. The cytosolic events in preprotein targeting remain largely unknown, although cytoplasmic chaperones have been proposed to facilitate delivery to the TOC complex. Preprotein recognition is mediated by the TOC GTPase receptors Toc159 and Toc34. The receptors constitute a GTP-regulated switch, which initiates membrane translocation via Toc75, a member of the Omp85 (outer membrane protein 85)/TpsB (two-partner secretion system B) family of bacterial, plastid and mitochondrial β-barrel outer membrane proteins. The TOC receptor systems have diversified to recognize distinct sets of preproteins, thereby maximizing the efficiency of targeting in response to changes in gene expression during developmental and physiological events that impact organelle function. The TOC complex interacts with the TIC translocon to allow simultaneous translocation of preproteins across the envelope. Both the two inner membrane complexes, the Tic110 and 1 MDa complexes, have been implicated as constituents of the TIC translocon, and it remains to be determined how they interact to form the TIC channel and assemble the import-associated chaperone network in the stroma that drives import across the envelope membranes. This review will focus on recent developments in our understanding of the mechanisms and diversity of the TOC-TIC systems. Our goal is to incorporate these recent studies with previous work and present updated or revised models for the function of TOC-TIC in protein import.
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Affiliation(s)
- Yamuna D Paila
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
| | - Lynn G L Richardson
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
| | - Danny J Schnell
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
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Salas JJ, Martínez-Force E, Harwood JL, Venegas-Calerón M, Aznar-Moreno JA, Moreno-Pérez AJ, Ruíz-López N, Serrano-Vega MJ, Graham IA, Mullen RT, Garcés R. Biochemistry of high stearic sunflower, a new source of saturated fats. Prog Lipid Res 2014; 55:30-42. [DOI: 10.1016/j.plipres.2014.05.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 05/12/2014] [Accepted: 05/12/2014] [Indexed: 01/01/2023]
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Richardson LGL, Clendening EA, Sheen H, Gidda SK, White KA, Mullen RT. A unique N-terminal sequence in the Carnation Italian ringspot virus p36 replicase-associated protein interacts with the host cell ESCRT-I component Vps23. J Virol 2014; 88:6329-44. [PMID: 24672030 PMCID: PMC4093892 DOI: 10.1128/jvi.03840-13] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 03/18/2014] [Indexed: 01/24/2023] Open
Abstract
UNLABELLED Like most positive-strand RNA viruses, infection by plant tombusviruses results in extensive rearrangement of specific host cell organelle membranes that serve as the sites of viral replication. The tombusvirus Tomato bushy stunt virus (TBSV) replicates within spherules derived from the peroxisomal boundary membrane, a process that involves the coordinated action of various viral and cellular factors, including constituents of the endosomal sorting complex required for transport (ESCRT). ESCRT is comprised of a series of protein subcomplexes (i.e., ESCRT-0 -I, -II, and -III) that normally participate in late endosome biogenesis and some of which are also hijacked by certain enveloped retroviruses (e.g., HIV) for viral budding from the plasma membrane. Here we show that the replication of Carnation Italian ringspot virus (CIRV), a tombusvirus that replicates at mitochondrial membranes also relies on ESCRT. In plant cells, CIRV recruits the ESCRT-I protein, Vps23, to mitochondria through an interaction that involves a unique region in the N terminus of the p36 replicase-associated protein that is not conserved in TBSV or other peroxisome-targeted tombusviruses. The interaction between p36 and Vps23 also involves the Vps23 C-terminal steadiness box domain and not its N-terminal ubiquitin E2 variant domain, which in the case of TBSV (and enveloped retroviruses) mediates the interaction with ESCRT. Overall, these results provide evidence that CIRV uses a unique N-terminal sequence for the recruitment of Vps23 that is distinct from those used by TBSV and certain mammalian viruses for ESCRT recruitment. Characterization of this novel interaction with Vps23 contributes to our understanding of how CIRV may have evolved to exploit key differences in the plant ESCRT machinery. IMPORTANCE Positive-strand RNA viruses replicate their genomes in association with specific host cell membranes. To accomplish this, cellular components responsible for membrane biogenesis and modeling are appropriated by viral proteins and redirected to assemble membrane-bound viral replicase complexes. The diverse pathways leading to the formation of these replication structures are poorly understood. We have determined that the cellular ESCRT system that is normally responsible for mediating late endosome biogenesis is also involved in the replication of the tombusvirus Carnation Italian ringspot virus (CIRV) at mitochondria. Notably, CIRV recruits ESCRT to the mitochondrial outer membrane via an interaction between a unique motif in the viral protein p36 and the ESCRT component Vps23. Our findings provide new insights into tombusvirus replication and the virus-induced remodeling of plant intracellular membranes, as well as normal ESCRT assembly in plants.
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Affiliation(s)
- Lynn G. L. Richardson
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Eric A. Clendening
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Hyukho Sheen
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Satinder K. Gidda
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - K. Andrew White
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Robert T. Mullen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
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Niehaus TD, Richardson LG, Gidda SK, ElBadawi-Sidhu M, Meissen JK, Mullen RT, Fiehn O, Hanson AD. Plants utilize a highly conserved system for repair of NADH and NADPH hydrates. PLANT PHYSIOLOGY 2014; 165:52-61. [PMID: 24599492 PMCID: PMC4012604 DOI: 10.1104/pp.114.236539] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 03/04/2014] [Indexed: 05/22/2023]
Abstract
NADH and NADPH undergo spontaneous and enzymatic reactions that produce R and S forms of NAD(P)H hydrates [NAD(P)HX], which are not electron donors and inhibit various dehydrogenases. In bacteria, yeast (Saccharomyces cerevisiae), and mammals, these hydrates are repaired by the tandem action of an ADP- or ATP-dependent dehydratase that converts (S)-NAD(P)HX to NAD(P)H and an epimerase that facilitates interconversion of the R and S forms. Plants have homologs of both enzymes, the epimerase homolog being fused to the vitamin B6 salvage enzyme pyridoxine 5'-phosphate oxidase. Recombinant maize (Zea mays) and Arabidopsis (Arabidopsis thaliana) NAD(P)HX dehydratases (GRMZM5G840928, At5g19150) were able to reconvert (S)-NAD(P)HX to NAD(P)H in an ATP-dependent manner. Recombinant maize and Arabidopsis epimerases (GRMZM2G061988, At5g49970) rapidly interconverted (R)- and (S)-NAD(P)HX, as did a truncated form of the Arabidopsis epimerase lacking the pyridoxine 5'-phosphate oxidase domain. All plant NAD(P)HX dehydratase and epimerase sequences examined had predicted organellar targeting peptides with a potential second start codon whose use would eliminate the targeting peptide. In vitro transcription/translation assays confirmed that both start sites were used. Dual import assays with purified pea (Pisum sativum) chloroplasts and mitochondria, and subcellular localization of GFP fusion constructs in tobacco (Nicotiana tabacum) suspension cells, indicated mitochondrial, plastidial, and cytosolic localization of the Arabidopsis epimerase and dehydratase. Ablation of the Arabidopsis dehydratase gene raised seedling levels of all NADHX forms by 20- to 40-fold, and levels of one NADPHX form by 10- to 30-fold. We conclude that plants have a canonical two-enzyme NAD(P)HX repair system that is directed to three subcellular compartments via the use of alternative translation start sites.
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Molecular characterization and expression analysis of chloroplast protein import components in tomato (Solanum lycopersicum). PLoS One 2014; 9:e95088. [PMID: 24751891 PMCID: PMC3994019 DOI: 10.1371/journal.pone.0095088] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 03/22/2014] [Indexed: 01/13/2023] Open
Abstract
The translocon at the outer envelope membrane of chloroplasts (Toc) mediates the recognition and initial import into the organelle of thousands of nucleus-encoded proteins. These proteins are translated in the cytosol as precursor proteins with cleavable amino-terminal targeting sequences called transit peptides. The majority of the known Toc components that mediate chloroplast protein import were originally identified in pea, and more recently have been studied most extensively in Arabidopsis. With the completion of the tomato genome sequencing project, it is now possible to identify putative homologues of the chloroplast import components in tomato. In the work reported here, the Toc GTPase cDNAs from tomato were identified, cloned and analyzed. The analysis revealed that there are four Toc159 homologues (slToc159-1, -2, -3 and -4) and two Toc34 homologues (slToc34-1 and -2) in tomato, and it was shown that tomato Toc159 and Toc34 homologues share high sequence similarity with the comparable import apparatus components from Arabidopsis and pea. Thus, tomato is a valid model for further study of this system. The expression level of Toc complex components was also investigated in different tissues during tomato development. The two tomato Toc34 homologues are expressed at higher levels in non-photosynthetic tissues, whereas, the expression of two tomato Toc159 homologues, slToc159-1 and slToc159-4, were higher in photosynthetic tissues, and the expression patterns of slToc159-2 was not significantly different in photosynthetic and non-photosynthetic tissues, and slToc159-3 expression was limited to a few select tissues.
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Aznar-Moreno JA, Venegas Calerón M, Martínez-Force E, Garcés R, Mullen R, Gidda SK, Salas JJ. Sunflower (Helianthus annuus) long-chain acyl-coenzyme A synthetases expressed at high levels in developing seeds. PHYSIOLOGIA PLANTARUM 2014; 150:363-73. [PMID: 24102504 DOI: 10.1111/ppl.12107] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Revised: 08/27/2013] [Accepted: 08/29/2013] [Indexed: 05/18/2023]
Abstract
Long chain fatty acid synthetases (LACSs) activate the fatty acid chains produced by plastidial de novo biosynthesis to generate acyl-CoA derivatives, important intermediates in lipid metabolism. Oilseeds, like sunflower, accumulate high levels of triacylglycerols (TAGs) in their seeds to nourish the embryo during germination. This requires that sunflower seed endosperm supports very active glycerolipid synthesis during development. Sunflower seed plastids produce large amounts of fatty acids, which must be activated through the action of LACSs, in order to be incorporated into TAGs. We cloned two different LACS genes from developing sunflower endosperm, HaLACS1 and HaLACS2, which displayed sequence homology with Arabidopsis LACS9 and LACS8 genes, respectively. These genes were expressed at high levels in developing seeds and exhibited distinct subcellular distributions. We generated constructs in which these proteins were fused to green fluorescent protein and performed transient expression experiments in tobacco cells. The HaLACS1 protein associated with the external envelope of tobacco chloroplasts, whereas HaLACS2 was strongly bound to the endoplasmic reticulum. Finally, both proteins were overexpressed in Escherichia coli and recovered as active enzymes in the bacterial membranes. Both enzymes displayed similar substrate specificities, with a very high preference for oleic acid and weaker activity toward stearic acid. On the basis of our findings, we discuss the role of these enzymes in sunflower oil synthesis.
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Affiliation(s)
- Jose A Aznar-Moreno
- Instituto de la Grasa (CSIC), Department of Biochemistry and Molecular Biology of Plant Products, 41012, Sevilla, Spain
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Richardson LGL, Paila YD, Siman SR, Chen Y, Smith MD, Schnell DJ. Targeting and assembly of components of the TOC protein import complex at the chloroplast outer envelope membrane. FRONTIERS IN PLANT SCIENCE 2014; 5:269. [PMID: 24966864 PMCID: PMC4052903 DOI: 10.3389/fpls.2014.00269] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 05/24/2014] [Indexed: 05/20/2023]
Abstract
The translocon at the outer envelope membrane of chloroplasts (TOC) initiates the import of thousands of nuclear encoded preproteins required for chloroplast biogenesis and function. The multimeric TOC complex contains two GTP-regulated receptors, Toc34 and Toc159, which recognize the transit peptides of preproteins and initiate protein import through a β-barrel membrane channel, Toc75. Different isoforms of Toc34 and Toc159 assemble with Toc75 to form structurally and functionally diverse translocons, and the composition and levels of TOC translocons is required for the import of specific subsets of coordinately expressed proteins during plant growth and development. Consequently, the proper assembly of the TOC complexes is key to ensuring organelle homeostasis. This review will focus on our current knowledge of the targeting and assembly of TOC components to form functional translocons at the outer membrane. Our analyses reveal that the targeting of TOC components involves elements common to the targeting of other outer membrane proteins, but also include unique features that appear to have evolved to specifically facilitate assembly of the import apparatus.
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Affiliation(s)
- Lynn G. L. Richardson
- Department of Biochemistry and Molecular Biology, University of Massachusetts, AmherstMA, USA
| | - Yamuna D. Paila
- Department of Biochemistry and Molecular Biology, University of Massachusetts, AmherstMA, USA
| | - Steven R. Siman
- Department of Biology, Wilfrid Laurier University, WaterlooON, Canada
| | - Yi Chen
- Department of Biology, Wilfrid Laurier University, WaterlooON, Canada
| | - Matthew D. Smith
- Department of Biology, Wilfrid Laurier University, WaterlooON, Canada
| | - Danny J. Schnell
- Department of Biochemistry and Molecular Biology, University of Massachusetts, AmherstMA, USA
- *Correspondence: Danny J. Schnell, Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Life Sciences Laboratories, Room N431, 240 Thatcher Way, Amherst, MA 01003-9364, USA e-mail:
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Lee J, Kim DH, Hwang I. Specific targeting of proteins to outer envelope membranes of endosymbiotic organelles, chloroplasts, and mitochondria. FRONTIERS IN PLANT SCIENCE 2014; 5:173. [PMID: 24808904 PMCID: PMC4010795 DOI: 10.3389/fpls.2014.00173] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Accepted: 04/10/2014] [Indexed: 05/21/2023]
Abstract
Chloroplasts and mitochondria are endosymbiotic organelles thought to be derived from endosymbiotic bacteria. In present-day eukaryotic cells, these two organelles play pivotal roles in photosynthesis and ATP production. In addition to these major activities, numerous reactions, and cellular processes that are crucial for normal cellular functions occur in chloroplasts and mitochondria. To function properly, these organelles constantly communicate with the surrounding cellular compartments. This communication includes the import of proteins, the exchange of metabolites and ions, and interactions with other organelles, all of which heavily depend on membrane proteins localized to the outer envelope membranes. Therefore, correct and efficient targeting of these membrane proteins, which are encoded by the nuclear genome and translated in the cytosol, is critically important for organellar function. In this review, we summarize the current knowledge of the mechanisms of protein targeting to the outer membranes of mitochondria and chloroplasts in two different directions, as well as targeting signals and cytosolic factors.
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Affiliation(s)
- Junho Lee
- Cellular Systems Biology, Department of Life Sciences, Pohang University of Science and TechnologyPohang, South Korea
| | - Dae Heon Kim
- Cellular Systems Biology, Department of Life Sciences, Pohang University of Science and TechnologyPohang, South Korea
| | - Inhwan Hwang
- Cellular Systems Biology, Department of Life Sciences, Pohang University of Science and TechnologyPohang, South Korea
- Division of Integrative Biosciences and Bioengineering, Pohang University of Science and TechnologyPohang, South Korea
- *Correspondence: Inhwan Hwang, Cellular Systems Biology, Department of Life Sciences and Division of Integrative Biosciences and Bioengineering, Pohang University of Science and Technology, Hyojadong, Nam-Gu, Pohang 790-784, South Korea e-mail:
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Marty NJ, Teresinski HJ, Hwang YT, Clendening EA, Gidda SK, Sliwinska E, Zhang D, Miernyk JA, Brito GC, Andrews DW, Dyer JM, Mullen RT. New insights into the targeting of a subset of tail-anchored proteins to the outer mitochondrial membrane. FRONTIERS IN PLANT SCIENCE 2014; 5:426. [PMID: 25237314 PMCID: PMC4154396 DOI: 10.3389/fpls.2014.00426] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 08/12/2014] [Indexed: 05/21/2023]
Abstract
Tail-anchored (TA) proteins are a unique class of functionally diverse membrane proteins defined by their single C-terminal membrane-spanning domain and their ability to insert post-translationally into specific organelles with an Ncytoplasm-Corganelle interior orientation. The molecular mechanisms by which TA proteins are sorted to the proper organelles are not well-understood. Herein we present results indicating that a dibasic targeting motif (i.e., -R-R/K/H-X({X≠E})) identified previously in the C terminus of the mitochondrial isoform of the TA protein cytochrome b 5, also exists in many other A. thaliana outer mitochondrial membrane (OMM)-TA proteins. This motif is conspicuously absent, however, in all but one of the TA protein subunits of the translocon at the outer membrane of mitochondria (TOM), suggesting that these two groups of proteins utilize distinct biogenetic pathways. Consistent with this premise, we show that the TA sequences of the dibasic-containing proteins are both necessary and sufficient for targeting to mitochondria, and are interchangeable, while the TA regions of TOM proteins lacking a dibasic motif are necessary, but not sufficient for localization, and cannot be functionally exchanged. We also present results from a comprehensive mutational analysis of the dibasic motif and surrounding sequences that not only greatly expands the functional definition and context-dependent properties of this targeting signal, but also led to the identification of other novel putative OMM-TA proteins. Collectively, these results provide important insight to the complexity of the targeting pathways involved in the biogenesis of OMM-TA proteins and help define a consensus targeting motif that is utilized by at least a subset of these proteins.
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Affiliation(s)
- Naomi J. Marty
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Howard J. Teresinski
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Yeen Ting Hwang
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Eric A. Clendening
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Satinder K. Gidda
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
| | - Elwira Sliwinska
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
- Department of Plant Genetics, Physiology and Biotechnology, University of Technology and Life Sciences in BydgoszczBydgoszcz, Poland
| | - Daiyuan Zhang
- United States Department of Agriculture, Agricultural Research Service, US Arid-Land Agricultural Research CenterMaricopa, AZ, USA
| | - Ján A. Miernyk
- United States Department of Agriculture, Agricultural Research Service, Plant Genetics Research Unit, University of MissouriColumbia, MO, USA
| | - Glauber C. Brito
- Instituto do Cancer do Estado de Sao Paulo, Fundacao Faculdade de Medicina, Universidade de Sao PauloSao Paulo, Brazil
| | - David W. Andrews
- Sunnybrook Research Institute and Department of Biochemistry, University of TorontoToronto, ON, Canada
| | - John M. Dyer
- United States Department of Agriculture, Agricultural Research Service, US Arid-Land Agricultural Research CenterMaricopa, AZ, USA
| | - Robert T. Mullen
- Department of Molecular and Cellular Biology, University of GuelphGuelph, ON, Canada
- *Correspondence: Robert T. Mullen, Department of Molecular and Cellular, Biology, University of Guelph, Room 4470 Science Complex, 488 Gordon Street, Guelph, ON N1G 2W1, Canada e-mail:
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Park S, Gidda SK, James CN, Horn PJ, Khuu N, Seay DC, Keereetaweep J, Chapman KD, Mullen RT, Dyer JM. The α/β hydrolase CGI-58 and peroxisomal transport protein PXA1 coregulate lipid homeostasis and signaling in Arabidopsis. THE PLANT CELL 2013; 25:1726-39. [PMID: 23667126 PMCID: PMC3694702 DOI: 10.1105/tpc.113.111898] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Revised: 04/17/2013] [Accepted: 04/23/2013] [Indexed: 05/21/2023]
Abstract
COMPARATIVE GENE IDENTIFICATION-58 (CGI-58) is a key regulator of lipid metabolism and signaling in mammals, but its underlying mechanisms are unclear. Disruption of CGI-58 in either mammals or plants results in a significant increase in triacylglycerol (TAG), suggesting that CGI-58 activity is evolutionarily conserved. However, plants lack proteins that are important for CGI-58 activity in mammals. Here, we demonstrate that CGI-58 functions by interacting with the PEROXISOMAL ABC-TRANSPORTER1 (PXA1), a protein that transports a variety of substrates into peroxisomes for their subsequent metabolism by β-oxidation, including fatty acids and lipophilic hormone precursors of the jasmonate and auxin biosynthetic pathways. We also show that mutant cgi-58 plants display changes in jasmonate biosynthesis, auxin signaling, and lipid metabolism consistent with reduced PXA1 activity in planta and that, based on the double mutant cgi-58 pxa1, PXA1 is epistatic to CGI-58 in all of these processes. However, CGI-58 was not required for the PXA1-dependent breakdown of TAG in germinated seeds. Collectively, the results reveal that CGI-58 positively regulates many aspects of PXA1 activity in plants and that these two proteins function to coregulate lipid metabolism and signaling, particularly in nonseed vegetative tissues. Similarities and differences of CGI-58 activity in plants versus animals are discussed.
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Affiliation(s)
- Sunjung Park
- U.S. Department of Agriculture–Agricultural Research Service, U.S. Arid-Land Agricultural Research Center, Maricopa, Arizona 85138
- Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203
| | - Satinder K. Gidda
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - Christopher N. James
- Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203
| | - Patrick J. Horn
- Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203
| | - Nicholas Khuu
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - Damien C. Seay
- U.S. Department of Agriculture–Agricultural Research Service, U.S. Arid-Land Agricultural Research Center, Maricopa, Arizona 85138
| | - Jantana Keereetaweep
- Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203
| | - Kent D. Chapman
- Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203
| | - Robert T. Mullen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - John M. Dyer
- U.S. Department of Agriculture–Agricultural Research Service, U.S. Arid-Land Agricultural Research Center, Maricopa, Arizona 85138
- Address correspondence to
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Formighieri C, Cazzaniga S, Kuras R, Bassi R. Biogenesis of photosynthetic complexes in the chloroplast of Chlamydomonas reinhardtii requires ARSA1, a homolog of prokaryotic arsenite transporter and eukaryotic TRC40 for guided entry of tail-anchored proteins. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2013; 73:850-61. [PMID: 23167510 DOI: 10.1111/tpj.12077] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Revised: 11/13/2012] [Accepted: 11/15/2012] [Indexed: 05/08/2023]
Abstract
as1, for antenna size mutant 1, was obtained by insertion mutagenesis of the unicellular green alga Chlamydomonas reinhardtii. This strain has a low chlorophyll content, 8% with respect to the wild type, and displays a general reduction in thylakoid polypeptides. The mutant was found to carry an insertion into a homologous gene, prokaryotic arsenite transporter (ARSA), whose yeast and mammal counterparts were found to be involved in the targeting of tail-anchored (TA) proteins to cytosol-exposed membranes, essential for several cellular functions. Here we present the characterization in a photosynthetic organism of an insertion mutant in an ARSA-homolog gene. The ARSA1 protein was found to be localized in the cytosol, and yet its absence in as1 leads to a small chloroplast and a strongly decreased chlorophyll content per cell. ARSA1 appears to be required for optimal biogenesis of photosynthetic complexes because of its involvement in the accumulation of TOC34, an essential component of the outer chloroplast membrane translocon (TOC) complex, which, in turn, catalyzes the import of nucleus-encoded precursor polypeptides into the chloroplast. Remarkably, the effect of the mutation appears to be restricted to biogenesis of chlorophyll-binding polypeptides and is not compensated by the other ARSA homolog encoded by the C. reinhardtii genome, implying a non-redundant function.
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Affiliation(s)
- Cinzia Formighieri
- Dipartimento di Biotecnologie, Università di Verona, 15, Strada Le Grazie, I-37134 Verona, Italy
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41
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Kim DH, Hwang I. Direct targeting of proteins from the cytosol to organelles: the ER versus endosymbiotic organelles. Traffic 2013; 14:613-21. [PMID: 23331847 DOI: 10.1111/tra.12043] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Revised: 01/08/2013] [Accepted: 01/17/2013] [Indexed: 12/21/2022]
Abstract
In eukaryotic cells consisting of many different types of organelles, targeting of organellar proteins is one of the most fundamental cellular processes. Proteins belonging to the endoplasmic reticulum (ER), chloroplasts and mitochondria are targeted individually from the cytosol to their cognate organelles. As the targeting to these organelles occurs in the cytosol during or after translation, the most crucial aspect is how specific targeting to these three organelles can be achieved without interfering with other targeting pathways. For these organelles, multiple mechanisms are used for targeting proteins, but the exact mechanism used depends on the type of protein and organelle, the location of targeting signals in the protein and the location of the protein in the organelle. In this review, we discuss the various mechanisms involved in protein targeting to the ER, chloroplasts and mitochondria, and how the targeting specificity is determined for these organelles in plant cells.
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Affiliation(s)
- Dae Heon Kim
- Divisions of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, South Korea
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Sun F, Carrie C, Law S, Murcha MW, Zhang R, Law YS, Suen PK, Whelan J, Lim BL. AtPAP2 is a tail-anchored protein in the outer membrane of chloroplasts and mitochondria. PLANT SIGNALING & BEHAVIOR 2012; 7:927-32. [PMID: 22751362 PMCID: PMC3474687 DOI: 10.4161/psb.20769] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
To date, Arabidopsis purple acid phosphatase 2 (AtPAP2) is the only known plant protein that is dual-targeted to chloroplasts and mitochondria by a C-terminal targeting signal. Using in vitro organelle import and green fluorescence protein (GFP) localization assays, we showed that AtPAP2 is located on, but not imported across the outer membrane (OM) of chloroplasts and mitochondria and exposed its N-terminal enzymatic domain to the cytosol. It was also found that a short stretch of 30 amino acids (a.a.) at the C-terminal region (a.a. 615-644) that contains a stretch of 18 hydrophobic residues, a WYAK motif and 8 hydrophilic residues is sufficient for dual-targeting. Mutation of WYAK to WYAE had no effect on dual-targeting ability suggesting that the charge within this flanking region alone is not an important determinant for dual-targeting.
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Affiliation(s)
- Feng Sun
- School of Biological Sciences; The University of Hong Kong; Pokfulam, Hong Kong, China
| | - Chris Carrie
- Australian Research Council Centre of Excellence in Plant Energy Biology; University of Western Australia; Crawley, WA Australia
| | - Simon Law
- Australian Research Council Centre of Excellence in Plant Energy Biology; University of Western Australia; Crawley, WA Australia
| | - Monika W. Murcha
- Australian Research Council Centre of Excellence in Plant Energy Biology; University of Western Australia; Crawley, WA Australia
| | - Renshan Zhang
- School of Biological Sciences; The University of Hong Kong; Pokfulam, Hong Kong, China
| | - Yee Song Law
- School of Biological Sciences; The University of Hong Kong; Pokfulam, Hong Kong, China
| | - Pui Kit Suen
- School of Biological Sciences; The University of Hong Kong; Pokfulam, Hong Kong, China
| | - James Whelan
- Australian Research Council Centre of Excellence in Plant Energy Biology; University of Western Australia; Crawley, WA Australia
| | - Boon Leong Lim
- School of Biological Sciences; The University of Hong Kong; Pokfulam, Hong Kong, China
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Lung SC, Chuong SD. A transit peptide-like sorting signal at the C terminus directs the Bienertia sinuspersici preprotein receptor Toc159 to the chloroplast outer membrane. THE PLANT CELL 2012; 24:1560-78. [PMID: 22517318 PMCID: PMC3398564 DOI: 10.1105/tpc.112.096248] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2012] [Revised: 03/07/2012] [Accepted: 04/02/2012] [Indexed: 05/21/2023]
Abstract
Although Toc159 is known to be one of the key GTPase receptors for selective recognition of chloroplast preproteins, the mechanism for its targeting to the chloroplast surface remains unclear. To compare the targeting of these GTPase receptors, we identified two Toc159 isoforms and a Toc34 from Bienertia sinuspersici, a single-cell C₄ species with dimorphic chloroplasts in individual chlorenchyma cells. Fluorescent protein tagging and immunogold studies revealed that the localization patterns of Toc159 were distinctive from those of Toc34, suggesting different targeting pathways. Bioinformatics analyses indicated that the C-terminal tails (CTs) of Toc159 possess physicochemical and structural properties of chloroplast transit peptides (cTPs). These results were further confirmed by fluorescent protein tagging, which showed the targeting of CT fusion proteins to the chloroplast surface. The CT of Bs Toc159 in reverse orientation functioned as a cleavable cTP that guided the fluorescent protein to the stroma. Moreover, a Bs Toc34 mutant protein was retargeted to the chloroplast envelope using the CTs of Toc159 or reverse sequences of other cTPs, suggesting their conserved functions. Together, our data show that the C terminus and the central GTPase domain represent a novel dual domain-mediated sorting mechanism that might account for the partitioning of Toc159 between the cytosol and the chloroplast envelope for preprotein recognition.
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Affiliation(s)
| | - Simon D.X. Chuong
- Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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Cytosolic events involved in chloroplast protein targeting. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:245-52. [PMID: 22450030 DOI: 10.1016/j.bbamcr.2012.03.006] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 02/24/2012] [Accepted: 03/08/2012] [Indexed: 12/12/2022]
Abstract
Chloroplasts are unique organelles that are responsible for photosynthesis. Although chloroplasts contain their own genome, the majority of chloroplast proteins are encoded by the nuclear genome. These proteins are transported to the chloroplasts after translation in the cytosol. Chloroplasts contain three membrane systems (outer/inner envelope and thylakoid membranes) that subdivide the interior into three soluble compartments known as the intermembrane space, stroma, and thylakoid lumen. Several targeting mechanisms are required to deliver proteins to the correct chloroplast membrane or soluble compartment. These mechanisms have been extensively studied using purified chloroplasts in vitro. Prior to targeting these proteins to the various compartments of the chloroplast, they must be correctly sorted in the cytosol. To date, it is not clear how these proteins are sorted in the cytosol and then targeted to the chloroplasts. Recently, the cytosolic carrier protein AKR2 and its associated cofactor Hsp17.8 for outer envelope membrane proteins of chloroplasts were identified. Additionally, a mechanism for controlling unimported plastid precursors in the cytosol has been discovered. This review will mainly focus on recent findings concerning the possible cytosolic events that occur prior to protein targeting to the chloroplasts. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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45
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Ching SLK, Gidda SK, Rochon A, van Cauwenberghe OR, Shelp BJ, Mullen RT. Glyoxylate reductase isoform 1 is localized in the cytosol and not peroxisomes in plant cells. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2012; 54:152-68. [PMID: 22309191 DOI: 10.1111/j.1744-7909.2012.01103.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Glyoxylate reductase (GLYR) is a key enzyme in plant metabolism which catalyzes the detoxification of both photorespiratory glyoxylate and succinic semialdehdye, an intermediate of the γ-aminobutyrate (GABA) pathway. Two isoforms of GLYR exist in plants, GLYR1 and GLYR2, and while GLYR2 is known to be localized in plastids, GLYR1 has been reported to be localized in either peroxisomes or the cytosol. Here, we reappraised the intracellular localization of GLYR1 in Arabidopsis thaliana L. Heynh (ecotype Lansberg erecta) using both transiently-transformed suspension cells and stably-transformed plants, in combination with fluorescence microscopy. The results indicate that GLYR1 is localized exclusively to the cytosol regardless of the species, tissue and/or cell type, or exposure of plants to environmental stresses that would increase flux through the GABA pathway. Moreover, the C-terminal tripeptide sequence of GLYR1, -SRE, despite its resemblance to a type 1 peroxisomal targeting signal, is not sufficient for targeting to peroxisomes. Collectively, these results define the cytosol as the intracellular location of GLYR1 and provide not only important insight to the metabolic roles of GLYR1 and the compartmentation of the GABA and photorespiratory pathways in plant cells, but also serve as a useful reference for future studies of proteins proposed to be localized to peroxisomes and/or the cytosol.
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Affiliation(s)
- Steven L K Ching
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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46
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Kriechbaumer V, von Löffelholz O, Abell BM. Chaperone receptors: guiding proteins to intracellular compartments. PROTOPLASMA 2012; 249:21-30. [PMID: 21461941 DOI: 10.1007/s00709-011-0270-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2011] [Accepted: 03/02/2011] [Indexed: 05/04/2023]
Abstract
Despite mitochondria and chloroplasts having their own genome, 99% of mitochondrial proteins (Rehling et al., Nat Rev Mol Cell Biol 5:519-530, 2004) and more than 95% of chloroplast proteins (Soll, Curr Opin Plant Biol 5:529-535, 2002) are encoded by nuclear DNA, synthesised in the cytosol and imported post-translationally. Protein targeting to these organelles depends on cytosolic targeting factors, which bind to the precursor, and then interact with membrane receptors to deliver the precursor into a translocase. The molecular chaperones Hsp70 and Hsp90 have been widely implicated in protein targeting to mitochondria and chloroplasts, and receptors capable of recognising these chaperones have been identified at the surface of both these organelles (Schlegel et al., Mol Biol Evol 24:2763-2774, 2007). The role of these chaperone receptors is not fully understood, but they have been shown to increase the efficiency of protein targeting (Young et al., Cell 112:41-50, 2003; Qbadou et al., EMBO J 25:1836-1847, 2006). Whether these receptors contribute to the specificity of targeting is less clear. A class of chaperone receptors bearing tetratricopeptide repeat domains is able to specifically bind the highly conserved C terminus of Hsp70 and/or Hsp90. Interestingly, at least of one these chaperone receptors can be found on each organelle (Schlegel et al., Mol Biol Evol 24:2763-2774, 2007), which suggests a universal role in protein targeting for these chaperone receptors. This review will investigate the role that chaperone receptors play in targeting efficiency and specificity, as well as examining recent in silico approaches to find novel chaperone receptors.
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Kriechbaumer V, Abell BM. Chloroplast envelope protein targeting fidelity is independent of cytosolic components in dual organelle assays. FRONTIERS IN PLANT SCIENCE 2012; 3:148. [PMID: 22783268 PMCID: PMC3384937 DOI: 10.3389/fpls.2012.00148] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 06/14/2012] [Indexed: 05/22/2023]
Abstract
The general mechanisms of intracellular protein targeting are well established, and depend on a targeting sequence in the protein, which is recognized by a targeting factor. Once a membrane protein is delivered to the correct organelle its targeting sequence can be recognized by receptors and a translocase, leading to membrane insertion. However, the relative contribution of each step for generating fidelity and efficiency of the overall process has not been systematically addressed. Here, we use tail-anchored (TA) membrane proteins in cell-free competitive targeting assays to chloroplasts to show that targeting can occur efficiently and with high fidelity in the absence of all cytosolic components, suggesting that chloroplast envelope protein targeting is primarily dependent on events at the outer envelope. Efficiency of targeting was increased by the addition of complete cytosol, and by Hsp70 or Hsp90, depending on the protein, but none of these cytosolic components influenced the fidelity of targeting. Our results suggest that the main role of targeting factors in chloroplast localization is to increase targeting efficiency by maintaining recognition competency at the outer envelope.
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Affiliation(s)
| | - Ben M. Abell
- *Correspondence: Ben M. Abell, Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK. e-mail:
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Kim DH, Xu ZY, Na YJ, Yoo YJ, Lee J, Sohn EJ, Hwang I. Small heat shock protein Hsp17.8 functions as an AKR2A cofactor in the targeting of chloroplast outer membrane proteins in Arabidopsis. PLANT PHYSIOLOGY 2011; 157:132-46. [PMID: 21730198 PMCID: PMC3165864 DOI: 10.1104/pp.111.178681] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Accepted: 07/03/2011] [Indexed: 05/20/2023]
Abstract
Plastid proteins that are encoded by the nuclear genome and synthesized in the cytosol undergo posttranslational targeting to plastids. Ankyrin repeat protein 2A (AKR2A) and AKR2B were recently shown to be involved in the targeting of proteins to the plastid outer envelope. However, it remains unknown whether other factors are involved in this process. In this study, we investigated a factor involved in AKR2A-mediated protein targeting to chloroplasts in Arabidopsis (Arabidopsis thaliana). Hsp17.8, a member of the class I (CI) cytosolic small heat shock proteins (sHsps), was identified in interactions with AKR2A. The interaction between Hsp17.8 and AKR2A was further confirmed by coimmunoprecipitation experiments. The carboxyl-terminal ankyrin repeat domain of AKR2A was responsible for AKR2A binding to Hsp17.8. Other CI cytosolic sHsps also interact with AKR2A to varying degrees. Additionally, Hsp17.8 binds to chloroplasts in vitro and enhances AKR2A binding to chloroplasts. HSP17.8 was expressed under normal growth conditions, and its expression increased after heat shock. Hsp17.8 exists as a dimer under normal physiological conditions, and it is converted to high oligomeric complexes, ranging from 240 kD to greater than 480 kD, after heat shock. High levels of Hsp17.8 together with AKR2A resulted in increased plastid targeting of Outer Envelope Protein7 (OEP7), a plastid outer envelope protein expressed as a green fluorescent protein fusion protein. In contrast, artificial microRNA suppression of HSP17.8 and closely related CI cytosolic sHSPs in protoplasts resulted in a reduction of OEP7:green fluorescent protein targeting to plastids. Based on these data, we propose that Hsp17.8 functions as an AKR2A cofactor in targeting membrane proteins to plastid outer membranes under normal physiological conditions.
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vonLoeffelholz O, Kriechbaumer V, Ewan RA, Jonczyk R, Lehmann S, Young JC, Abell BM. OEP61 is a chaperone receptor at the plastid outer envelope. Biochem J 2011; 438:143-53. [PMID: 21612577 PMCID: PMC5026492 DOI: 10.1042/bj20110448] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Chloroplast precursor proteins encoded in the nucleus depend on their targeting sequences for delivery to chloroplasts. There exist different routes to the chloroplast outer envelope, but a common theme is the involvement of molecular chaperones. Hsp90 (heat-shock protein 90) delivers precursors via its receptor Toc64, which transfers precursors to the core translocase in the outer envelope. In the present paper, we identify an uncharacterized protein in Arabidopsis thaliana OEP61 which shares common features with Toc64, and potentially provides an alternative route to the chloroplasts. Sequence analysis indicates that OEP61 possesses a clamp-type TPR (tetratricopeptide repeat) domain capable of binding molecular chaperones, and a C-terminal TMD (transmembrane domain). Phylogenetic comparisons show sequence similarities between the TPR domain of OEP61 and those of the Toc64 family. Expression of mRNA and protein was detected in all plant tissues, and localization at the chloroplast outer envelope was demonstrated by a combination of microscopy and in vitro import assays. Binding assays show that OEP61 interacts specifically with Hsp70 (heat-shock protein 70) via its TPR clamp domain. Furthermore, OEP61 selectively recognizes chloroplast precursors via their targeting sequences, and a soluble form of OEP61 inhibits chloroplast targeting. We therefore propose that OEP61 is a novel chaperone receptor at the chloroplast outer envelope, mediating Hsp70-dependent protein targeting to chloroplasts.
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Affiliation(s)
| | - Verena Kriechbaumer
- Biomedical Research Centre, Sheffield Hallam University, Sheffield S1 1WB, U.K
| | - Richard A. Ewan
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PL, U.K
| | - Rafal Jonczyk
- Biomedical Research Centre, Sheffield Hallam University, Sheffield S1 1WB, U.K
| | - Susann Lehmann
- Biomedical Research Centre, Sheffield Hallam University, Sheffield S1 1WB, U.K
| | - Jason C. Young
- Department of Biochemistry, McGill University, Montreal H3G 0B1, Canada
| | - Ben M. Abell
- Biomedical Research Centre, Sheffield Hallam University, Sheffield S1 1WB, U.K
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50
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Bölter B, Soll J. Protein Import into Chloroplasts: Dealing with the (Membrane) Integration Problem. Chembiochem 2011; 12:1655-61. [DOI: 10.1002/cbic.201100118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Indexed: 11/10/2022]
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