1
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Hartojo A, Doyle MT. β-barrel membrane proteins fold via hybrid-barrel intermediate states. Curr Opin Struct Biol 2024; 87:102830. [PMID: 38728831 DOI: 10.1016/j.sbi.2024.102830] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2024] [Revised: 03/15/2024] [Accepted: 04/22/2024] [Indexed: 05/12/2024]
Abstract
Gram-negative bacteria and eukaryotic organelles of bacterial origin contain outer membrane proteins that possess a transmembrane "β-barrel" domain. The conserved β-barrel assembly machine (BAM) and the sorting and assembly machine (SAM) are required for the folding and membrane insertion of β-barrels in Gram-negative bacteria and mitochondria, respectively. Although the mechanisms by which β-barrels are folded are incompletely understood, advances in cryo-electron microscopy (cryo-EM) have recently yielded unprecedented insights into their folding process. Here we highlight recent studies that show that both bacterial and mitochondrial β-barrels fold via the formation of remarkable "hybrid-barrel" intermediate states during their interaction with the folding machinery. We discuss how these results align with a general model of β-barrel folding.
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Affiliation(s)
- Alfred Hartojo
- Sydney Infectious Diseases Institute, The University of Sydney, Darlington, New South Wales, Australia; School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, Darlington, New South Wales, Australia. https://twitter.com/AlfredHartojo29
| | - Matthew Thomas Doyle
- Sydney Infectious Diseases Institute, The University of Sydney, Darlington, New South Wales, Australia; School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, Darlington, New South Wales, Australia.
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2
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Yoshimura R, Minamikawa S, Suzuki T, Goto K, Latrasse D, Sicar S, Raynaud C, Benhamed M, Yoshioka Y. CRUMPLED LEAF supports plastid OUTER ENVELOPE PROTEIN OF 80 KDA complex formation in Arabidopsis. PLANT PHYSIOLOGY 2024; 194:2422-2433. [PMID: 38235762 DOI: 10.1093/plphys/kiae005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Revised: 11/17/2023] [Accepted: 11/22/2023] [Indexed: 01/19/2024]
Abstract
Embedded β-barrel proteins in the outer envelope membrane mediate most cellular trafficking between the cytoplasm and plastids. Although the TRANSLOCON AT THE OUTER ENVELOPE MEMBRANE OF CHLOROPLASTS 75-V (TOC75-V)/OUTER ENVELOPE PROTEIN OF 80 KDA (OEP80) complex has been implicated in the insertion and assembly of β-barrel proteins in the outer envelope membrane of Arabidopsis (Arabidopsis thaliana) chloroplasts, relatively little is known about this process. CRUMPLED LEAF (CRL) encodes a chloroplast outer envelope membrane-localized protein, and its loss-of-function mutation results in pleiotropic defects, including altered plant morphogenesis, growth retardation, suppression of plastid division, and spontaneous light intensity-dependent localized cell death. A suppressor screen conducted on mutagenized crl mutants revealed that a missense mutation in OEP80 suppresses the pleiotropic defects of crl. Furthermore, we found that OEP80 complex formation is compromised in crl. Additionally, we demonstrated that CRL interacts with OEP80 in vivo and that a portion of CRL is present at the same molecular weight as the OEP80 complex. Our results suggest that CRL interacts with OEP80 to facilitate its complex formation. CRL is involved in plastid protein import; therefore, the pleiotropic defects in crl are likely due to the combined effects of decreased plastid protein import and altered membrane integration of β-barrel proteins in the outer envelope membrane. This study sheds light on the mechanisms that allow β-barrel protein integration into the plastid outer envelope membrane and the importance of this finding for plant cellular processes.
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Affiliation(s)
- Ryo Yoshimura
- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Syun Minamikawa
- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Takamasa Suzuki
- Department of Biological Chemistry, College of Bioscience and Biotechnology, Chubu University, 1200 Matsumoto-cho, Kasugai, Aichi 487-8501, Japan
| | - Kotaro Goto
- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - David Latrasse
- CNRS, INRAE, Univ Evry, Institute of Plant Sciences Paris-Saclay (IPS2), Université Paris-Saclay, 91405 Orsay, France
- CNRS, INRAE, Institute of Plant Sciences Paris-Saclay (IPS2), Université de Paris, 91405 Orsay, France
| | - Sanchari Sicar
- CNRS, INRAE, Univ Evry, Institute of Plant Sciences Paris-Saclay (IPS2), Université Paris-Saclay, 91405 Orsay, France
- CNRS, INRAE, Institute of Plant Sciences Paris-Saclay (IPS2), Université de Paris, 91405 Orsay, France
| | - Cécile Raynaud
- CNRS, INRAE, Univ Evry, Institute of Plant Sciences Paris-Saclay (IPS2), Université Paris-Saclay, 91405 Orsay, France
- CNRS, INRAE, Institute of Plant Sciences Paris-Saclay (IPS2), Université de Paris, 91405 Orsay, France
| | - Moussa Benhamed
- CNRS, INRAE, Univ Evry, Institute of Plant Sciences Paris-Saclay (IPS2), Université Paris-Saclay, 91405 Orsay, France
- CNRS, INRAE, Institute of Plant Sciences Paris-Saclay (IPS2), Université de Paris, 91405 Orsay, France
- Institut Universitaire de France (IUF)
| | - Yasushi Yoshioka
- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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3
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Moitra A, Tiku V, Rapaport D. Yeast mitochondria can process de novo designed β-barrel proteins. FEBS J 2024; 291:292-307. [PMID: 37723586 DOI: 10.1111/febs.16950] [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: 12/29/2022] [Revised: 08/18/2023] [Accepted: 09/04/2023] [Indexed: 09/20/2023]
Abstract
Mitochondrial outer membrane β-barrel proteins are encoded in the nucleus, translated in the cytosol and then targeted to and imported into the respective organelles. Detailed studies have uncovered the mechanisms involved in the import of these proteins and identified the targeting signals and the cytosolic factors that govern their proper biogenesis. Recently, de novo designed eight-stranded β-barrel proteins (Tmb2.3 and Tmb2.17) were shown to fold and assemble into lipid membranes. To better understand the general aspects of the biogenesis of β-barrel proteins, we investigated the fate of these artificial proteins upon their expression in yeast cells. We demonstrate that although these proteins are de novo designed and are not related to bona fide mitochondrial β-barrel proteins, they were targeted to mitochondria and integrated into the organelle outer membrane. We further studied whether this integration requires components of the yeast mitochondrial import machinery like Tom20, Tom70, Tob55/Sam50 and Mas37/Sam37. Whereas it seems that none of the import receptors was required for the biogenesis of the artificial β-barrel proteins, we observed a strong dependency on the TOB/SAM complex. Collectively, our findings demonstrate that the mitochondrial outer membrane is the preferential location in yeast cells for any membrane-embedded β-barrel protein.
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Affiliation(s)
- Anasuya Moitra
- Interfaculty Institute of Biochemistry, University of Tuebingen, Tuebingen, Germany
| | - Vitasta Tiku
- Interfaculty Institute of Biochemistry, University of Tuebingen, Tuebingen, Germany
| | - Doron Rapaport
- Interfaculty Institute of Biochemistry, University of Tuebingen, Tuebingen, Germany
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4
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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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5
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Mayse LA, Movileanu L. Gating of β-Barrel Protein Pores, Porins, and Channels: An Old Problem with New Facets. Int J Mol Sci 2023; 24:12095. [PMID: 37569469 PMCID: PMC10418385 DOI: 10.3390/ijms241512095] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 07/23/2023] [Accepted: 07/25/2023] [Indexed: 08/13/2023] Open
Abstract
β barrels are ubiquitous proteins in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria. These transmembrane proteins (TMPs) execute a wide variety of tasks. For example, they can serve as transporters, receptors, membrane-bound enzymes, as well as adhesion, structural, and signaling elements. In addition, multimeric β barrels are common structural scaffolds among many pore-forming toxins. Significant progress has been made in understanding the functional, structural, biochemical, and biophysical features of these robust and versatile proteins. One frequently encountered fundamental trait of all β barrels is their voltage-dependent gating. This process consists of reversible or permanent conformational transitions between a large-conductance, highly permeable open state and a low-conductance, solute-restrictive closed state. Several intrinsic molecular mechanisms and environmental factors modulate this universal property of β barrels. This review article outlines the typical signatures of voltage-dependent gating. Moreover, we discuss recent developments leading to a better qualitative understanding of the closure dynamics of these TMPs.
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Affiliation(s)
- Lauren A. Mayse
- Department of Physics, Syracuse University, 201 Physics Building, Syracuse, NY 13244, USA;
- Department of Biomedical and Chemical Engineering, Syracuse University, 223 Link Hall, Syracuse, NY 13244, USA
| | - Liviu Movileanu
- Department of Physics, Syracuse University, 201 Physics Building, Syracuse, NY 13244, USA;
- Department of Biomedical and Chemical Engineering, Syracuse University, 223 Link Hall, Syracuse, NY 13244, USA
- The BioInspired Institute, Syracuse University, Syracuse, NY 13244, USA
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6
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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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7
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Kumar S, Ruiz N. Bacterial AsmA-Like Proteins: Bridging the Gap in Intermembrane Phospholipid Transport. CONTACT (THOUSAND OAKS (VENTURA COUNTY, CALIF.)) 2023; 6:25152564231185931. [PMID: 37455811 PMCID: PMC10345924 DOI: 10.1177/25152564231185931] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 06/16/2023] [Accepted: 06/16/2023] [Indexed: 07/18/2023]
Abstract
In eukaryotic cells, nonvesicular lipid transport between organelles is mediated by lipid-transfer proteins. Recently, a new class of these lipid transporters has been described to facilitate the bulk of inter-organelle lipid transport at contact sites by forming bridge-like structures with a hydrophobic groove through which lipids travel. Because their predicted structure is composed of repeating β-groove (RBG) domains, they have been named the RBG protein superfamily. Early studies on RBG proteins VPS13 and ATG2 recognized the resemblance of their predicted structures to that of the bacterial Lpt system, which transports newly synthesized lipopolysaccharides (LPS) between the inner and the outer membranes (IMs and OMs) of Gram-negative bacteria. In these didermic bacteria, the IMs and OMs are separated by an aqueous periplasmic compartment that is traversed by a bridge-like structure built with β-jelly roll domains from several Lpt proteins that provides a hydrophobic groove for LPS molecules to travel across the periplasm. Despite structural and functional similarities between RBG proteins and the Lpt system, the bacterial AsmA-like protein family has recently emerged as the likely ancestor of RBG proteins and long sought-after transporters that facilitate the transfer of phospholipids from the IM to the OM. Here, we review our current understanding of the structure and function of bacterial AsmA-like proteins, mainly focusing on recent studies that have led to the proposal that AsmA-like proteins mediate the bulk of phospholipid transfer between the IMs and OMs.
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Affiliation(s)
- Sujeet Kumar
- Department of Microbiology, The Ohio State University, Columbus, Ohio, USA
| | - Natividad Ruiz
- Department of Microbiology, The Ohio State University, Columbus, Ohio, USA
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8
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Doyle MT, Bernstein HD. Function of the Omp85 Superfamily of Outer Membrane Protein Assembly Factors and Polypeptide Transporters. Annu Rev Microbiol 2022; 76:259-279. [PMID: 35650668 DOI: 10.1146/annurev-micro-033021-023719] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The Omp85 protein superfamily is found in the outer membrane (OM) of all gram-negative bacteria and eukaryotic organelles of bacterial origin. Members of the family catalyze both the membrane insertion of β-barrel proteins and the translocation of proteins across the OM. Although the mechanism(s) by which these proteins function is unclear, striking new insights have emerged from recent biochemical and structural studies. In this review we discuss the entire Omp85 superfamily but focus on the function of the best-studied member, BamA, which is an essential and highly conserved component of the bacterial barrel assembly machinery (BAM). Because BamA has multiple functions that overlap with those of other Omp85 proteins, it is likely the prototypical member of the Omp85 superfamily. Furthermore, BamA has become a protein of great interest because of the recent discovery of small-molecule inhibitors that potentially represent an important new class of antibiotics. Expected final online publication date for the Annual Review of Microbiology, Volume 76 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Matthew Thomas Doyle
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA; ,
| | - Harris D Bernstein
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA; ,
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9
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Barth MA, Soll J, Akbaş Ş. Prokaryotic and eukaryotic traits support the biological role of the chloroplast outer envelope. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR CELL RESEARCH 2022; 1869:119224. [PMID: 35120999 DOI: 10.1016/j.bbamcr.2022.119224] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 01/22/2022] [Accepted: 01/26/2022] [Indexed: 06/14/2023]
Abstract
The plastid outer envelope (OE) is a mixture of components inherited from their prokaryotic ancestor like galactolipids, carotenoids and porin type ion channels supplemented with eukaryotic inventions to make the endosymbiotic process successful as well as to control plastid biogenesis and differentiation. In this review we wanted to highlight the importance of the OE proteins and its evolutionary origin. For a long time, the OE was thought to be a diffusion barrier only, but with the recent discoveries of all kinds of different proteins in the OE it has been shown that the OE can modulate various functions within the cell. The phenotypic changes show that channels like the outer envelope proteins OEP40, OEP16 or JASSY have a pronounced ion selectivity that cannot be replaced by other ion channels present in the OE. Eukaryotic additions, like the GTPase receptors Toc33 and Toc159 or the ubiquitin proteasome system for chloroplast protein quality control, round up the profile of the OE.
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Affiliation(s)
- Melanie Anette Barth
- Department Biologie 1, Botanik, Ludwig-Maximilians-Universität München, Großhaderner Str. 2-4, 82152 Planegg-Martinsried, Germany
| | - Jürgen Soll
- Department Biologie 1, Botanik, Ludwig-Maximilians-Universität München, Großhaderner Str. 2-4, 82152 Planegg-Martinsried, Germany.
| | - Şebnem Akbaş
- Department Biologie 1, Botanik, Ludwig-Maximilians-Universität München, Großhaderner Str. 2-4, 82152 Planegg-Martinsried, Germany
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10
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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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11
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Jeong J, Hwang I, Lee DW. Functional Organization of Sequence Motifs in Diverse Transit Peptides of Chloroplast Proteins. Front Physiol 2021; 12:795156. [PMID: 34880786 PMCID: PMC8645953 DOI: 10.3389/fphys.2021.795156] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 10/28/2021] [Indexed: 11/17/2022] Open
Abstract
Although the chloroplasts in plants are characterized by an inherent genome, the chloroplast proteome is composed of proteins encoded by not only the chloroplast genome but also the nuclear genome. Nuclear-encoded chloroplast proteins are synthesized on cytosolic ribosomes and post-translationally targeted to the chloroplasts. In the latter process, an N-terminal cleavable transit peptide serves as a targeting signal required for the import of nuclear-encoded chloroplast interior proteins. This import process is mediated via an interaction between the sequence motifs in transit peptides and the components of the TOC/TIC (translocon at the outer/inner envelope of chloroplasts) translocons. Despite a considerable diversity in primary structures, several common features have been identified among transit peptides, including N-terminal moderate hydrophobicity, multiple proline residues dispersed throughout the transit peptide, preferential usage of basic residues over acidic residues, and an absence of N-terminal arginine residues. In this review, we will recapitulate and discuss recent progress in our current understanding of the functional organization of sequence elements commonly present in diverse transit peptides, which are essential for the multi-step import of chloroplast proteins.
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Affiliation(s)
- Jinseung Jeong
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, South Korea
| | - Inhwan Hwang
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, South Korea
| | - Dong Wook Lee
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, South Korea.,Department of Bioenergy Science and Technology, Chonnam National University, Gwangju, South Korea
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12
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Wang Q, Guan Z, Qi L, Zhuang J, Wang C, Hong S, Yan L, Wu Y, Cao X, Cao J, Yan J, Zou T, Liu Z, Zhang D, Yan C, Yin P. Structural insight into the SAM-mediated assembly of the mitochondrial TOM core complex. Science 2021; 373:1377-1381. [PMID: 34446444 DOI: 10.1126/science.abh0704] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Qiang Wang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Zeyuan Guan
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Liangbo Qi
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Jinjin Zhuang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Chen Wang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Sixing Hong
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Ling Yan
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Yan Wu
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Xiaoqian Cao
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Jianbo Cao
- Public Laboratory of Electron Microscopy, Huazhong Agricultural University, Wuhan 430070, China
| | - Junjie Yan
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Tingting Zou
- College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
| | - Zhu Liu
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Delin Zhang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Chuangye Yan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Ping Yin
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
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13
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Moitra A, Rapaport D. The Biogenesis Process of VDAC - From Early Cytosolic Events to Its Final Membrane Integration. Front Physiol 2021; 12:732742. [PMID: 34456757 PMCID: PMC8388839 DOI: 10.3389/fphys.2021.732742] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 07/26/2021] [Indexed: 11/13/2022] Open
Abstract
Voltage dependent anion-selective channel (VDAC) is the most abundant protein in the mitochondrial outer membrane. It is a membrane embedded β-barrel protein composed of 19 mostly anti-parallel β-strands that form a hydrophilic pore. Similar to the vast majority of mitochondrial proteins, VDAC is encoded by nuclear DNA, and synthesized on cytosolic ribosomes. The protein is then targeted to the mitochondria while being maintained in an import competent conformation by specific cytosolic factors. Recent studies, using yeast cells as a model system, have unearthed the long searched for mitochondrial targeting signal for VDAC and the role of cytosolic chaperones and mitochondrial import machineries in its proper biogenesis. In this review, we summarize our current knowledge regarding the early cytosolic stages of the biogenesis of VDAC molecules, the specific targeting of VDAC to the mitochondrial surface, and the subsequent integration of VDAC into the mitochondrial outer membrane by the TOM and TOB/SAM complexes.
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Affiliation(s)
- Anasuya Moitra
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany
| | - Doron Rapaport
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany
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