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Chen L, Wang X, Wang L, Fang Y, Pan X, Gao X, Zhang W. Functional characterization of chloroplast transit peptide in the small subunit of Rubisco in maize. JOURNAL OF PLANT PHYSIOLOGY 2019; 237:12-20. [PMID: 30999073 DOI: 10.1016/j.jplph.2019.04.001] [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: 12/18/2018] [Revised: 04/04/2019] [Accepted: 04/04/2019] [Indexed: 06/09/2023]
Abstract
Functions of domains or motifs, which are encoded by the transit peptide (TP) of the precursor of the small subunit of Rubisco (prSSU), have been investigated intensively in dicots. Functional characterization of the prSSU TP, however, is still understudied in maize. In this study, we found that the TP of maize prSSU1 did not function fully in chloroplast targeting in Arabidopsis or vice versa, indicating the divergent function of TPs in chloroplast targeting between maize and Arabidopsis. Through deletion or substitution assays, we found that the N-terminal region of maize or Arabidopsis prSSU1 was necessary and sufficient for importing specifically the fused-green fluorescent protein (GFP) into each corresponding chloroplast. Finally, we found that the first-five amino acids and MM motif in the N-terminal domain of the maize TP played an essential role in maize chloroplast targeting. Thus, our analyses demonstrate that the N-terminal domain of the prSSU1 TP is the key determinant in chloroplast targeting between maize and Arabidopsis. Our study highlights the unique properties of the maize prSSU1 TP in chloroplast targeting, thus helping to understand the role of N-terminal domain in chloroplast targeting across species. It will help to manipulate chloroplast transit peptides (cTPs) for crop bioengineering.
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Affiliation(s)
- Lifen Chen
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, JiangSu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, No.1 Weigang, Nanjing, Jiangsu, 210095, China
| | - Ximeng Wang
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, JiangSu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, No.1 Weigang, Nanjing, Jiangsu, 210095, China
| | - Lei Wang
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, JiangSu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, No.1 Weigang, Nanjing, Jiangsu, 210095, China
| | - Yuan Fang
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, JiangSu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, No.1 Weigang, Nanjing, Jiangsu, 210095, China
| | - Xiucai Pan
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, JiangSu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, No.1 Weigang, Nanjing, Jiangsu, 210095, China
| | - Xiquan Gao
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, JiangSu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, No.1 Weigang, Nanjing, Jiangsu, 210095, China
| | - Wenli Zhang
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, JiangSu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, No.1 Weigang, Nanjing, Jiangsu, 210095, China.
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2
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Rao JLUM, Reddy PS, Mishra RN, Gupta D, Sahal D, Tuteja N, Sopory SK, Reddy MK. Thermo and pH stable ATP-independent chaperone activity of heat-inducible Hsp70 from Pennisetum glaucum. PLANT SIGNALING & BEHAVIOR 2010; 5:110-21. [PMID: 20023401 PMCID: PMC2884110 DOI: 10.4161/psb.5.2.10547] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Accepted: 11/09/2009] [Indexed: 05/24/2023]
Abstract
Heat shock proteins (Hsps) are a class of molecular chaperones that play an essential role in preserving cellular functions under stressful conditions. The over production of recombinant proteins often causes cellular stress that results in aggregation/misfolding of proteins, which sometimes leads to the formation of inclusion bodies. Here we report the cloning and characterization of heat-inducible PgHsp70 from Pennisetum glaucum, a heat and drought tolerant plant that showed stability and chaperone activity at elevated temperatures. The predicted amino acid sequence of PgHsp70 revealed a high homology with Hsp70 from other plants, and the overall 3D structure homology modeling is similar to that of the constitutively expressed bovine cytosolic Heat Shock Cognate (HSC)-70. The purified recombinant protein had an apparent molecular mass of 70 kDa and displayed optimal chaperone activity at 50 degrees C, and pH 8.0. Under these conditions, the T(1/2) of PgHsp70 increased from 10 to 15 h in the presence of glycerol. The PgHsp70 exhibited a higher chaperone activity towards glutamate dehydrogenase than alcohol dehydrogenase. The expression of recombinant carbonic anhydrase (CA) in E. coli in a catalytically active soluble form rather than in inclusion bodies was made feasible by co-expression of PgHsp70. Circular dichroism (CD) studies of the recombinant PgHsp70 did not reveal any discernible changes in the alpha-helix content, with increase in temperature from 35 to 85 degrees C, thus suggesting a critical role of alpha-helix content in maintaining the chaperone activity.
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Affiliation(s)
- J L Uma Maheswar Rao
- International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India
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3
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Inoue H, Ratnayake RMU, Nonami H, Akita M. Development and optimization of an in vitro chloroplastic protein import assay using recombinant proteins. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2008; 46:541-9. [PMID: 18417353 DOI: 10.1016/j.plaphy.2008.02.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Indexed: 05/26/2023]
Abstract
The in vitro protein import experiment is one of the most important techniques for determining protein localization. For chloroplastic proteins, proteins of interest are incubated with isolated chloroplasts in the presence of energy sources. Radio-labeled proteins synthesized either in vitro or in vivo have been widely used as substrate proteins. Here we report our development of the protein import assay system in which non-radio-labeled proteins, overexpressed in Escherichia coli, were applied. In this system, substrate proteins were designed to carry epitope-tags, thus allowing analysis of imported proteins by SDS-PAGE, followed by immunoblotting to detect these tags. Furthermore, the imported proteins were found to be incorporated into their native form. These observations indicated that recombinant proteins were imported into chloroplasts and folded correctly. Therefore, this assay system could represent another valuable tool for determining protein localization.
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Affiliation(s)
- Hitoshi Inoue
- The United Graduate School of Agricultural Science, Ehime University, 3-5-7 Tarumi, Matsuyama 790-8566, Japan
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4
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Sharma R, Soll J, Bölter B. Import and localisation of nucleoside diphosphate kinase 2 in chloroplasts. JOURNAL OF PLANT RESEARCH 2007; 120:451-6. [PMID: 17340056 DOI: 10.1007/s10265-007-0071-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2006] [Accepted: 12/13/2006] [Indexed: 05/14/2023]
Abstract
Nucleoside diphosphate kinases (NDPKs) are key enzymes that are involved in the homeostasis of nucleoside triphosphates (NTPs). Different isoforms exist, which are found in diverse cell compartments, for example the cytosol, mitochondria, and plant chloroplasts. NDPK2 of Pisum sativum has been shown to be localised in chloroplasts. Two forms of different size have been reported in plastids and it has been speculated that they function in distinct suborganellar compartments. We investigated the import behaviour and localisation of these two isoforms. Our results indicate that they do not differ in their route of entry into the organelle and both forms end up in the chloroplast stroma.
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Affiliation(s)
- Rita Sharma
- Department Biologie I, LMU München, Munich, Germany
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5
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Lee DW, Lee S, Lee GJ, Lee KH, Kim S, Cheong GW, Hwang I. Functional characterization of sequence motifs in the transit peptide of Arabidopsis small subunit of rubisco. PLANT PHYSIOLOGY 2006; 140:466-83. [PMID: 16384899 PMCID: PMC1361317 DOI: 10.1104/pp.105.074575] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The transit peptides of nuclear-encoded chloroplast proteins are necessary and sufficient for targeting and import of proteins into chloroplasts. However, the sequence information encoded by transit peptides is not fully understood. In this study, we investigated sequence motifs in the transit peptide of the small subunit of the Rubisco complex by examining the ability of various mutant transit peptides to target green fluorescent protein reporter proteins to chloroplasts in Arabidopsis (Arabidopsis thaliana) leaf protoplasts. We divided the transit peptide into eight blocks (T1 through T8), each consisting of eight or 10 amino acids, and generated mutants that had alanine (Ala) substitutions or deletions, of one or two T blocks in the transit peptide. In addition, we generated mutants that had the original sequence partially restored in single- or double-T-block Ala (A) substitution mutants. Analysis of chloroplast import of these mutants revealed several interesting observations. Single-T-block mutations did not noticeably affect targeting efficiency, except in T1 and T4 mutations. However, double-T mutants, T2A/T4A, T3A/T6A, T3A/T7A, T4A/T6A, and T4A/T7A, caused a 50% to 100% loss in targeting ability. T3A/T6A and T4A/T6A mutants produced only precursor proteins, whereas T2A/T4A and T4A/T7A mutants produced only a 37-kD protein. Detailed analyses revealed that sequence motifs ML in T1, LKSSA in T3, FP and RK in T4, CMQVW in T6, and KKFET in T7 play important roles in chloroplast targeting. In T1, the hydrophobicity of ML is important for targeting. LKSSA in T3 is functionally equivalent to CMQVW in T6 and KKFET in T7. Furthermore, subcellular fractionation revealed that Ala substitution in T1, T3, and T6 produced soluble precursors, whereas Ala substitution in T4 and T7 produced intermediates that were tightly associated with membranes. These results demonstrate that the transit peptide contains multiple motifs and that some of them act in concert or synergistically.
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Affiliation(s)
- Dong Wook Lee
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
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6
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Affiliation(s)
- Mark Paetzel
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
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7
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Richter S, Lamppa GK. Determinants for removal and degradation of transit peptides of chloroplast precursor proteins. J Biol Chem 2002; 277:43888-94. [PMID: 12235143 DOI: 10.1074/jbc.m206020200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The stromal processing peptidase (SPP) cleaves a large diversity of chloroplast precursor proteins, removing an N-terminal transit peptide. We predicted previously that this key step of the import pathway is mediated by features of the transit peptide that determine precursor binding and cleavage followed by transit peptide conversion to a degradable substrate. Here we performed competition experiments using synthesized oligopeptides of the transit peptide of ferredoxin precursor to investigate the mechanism of these processes. We found that binding and processing of ferredoxin precursor depend on specific interactions of SPP with the region consisting of the C-terminal 12 residues of the transit peptide. Analysis of four other precursors suggests that processing depends on the same region, although their transit peptides are highly divergent in primary sequence and length. Upon processing, SPP terminates its interaction with the transit peptide by a second cleavage, converting it to a subfragment form. From the competition experiments we deduce that SPP releases a subfragment consisting of the transit peptide without its original C terminus. Interestingly, examination of the ATP-dependent metallopeptidase activity responsible for degradation of transit peptide subfragments suggests that it may recognize other unrelated peptides and, hence, act separately from SPP as a novel stromal oligopeptidase.
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Affiliation(s)
- Stefan Richter
- Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637, USA
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8
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Apuya NR, Yadegari R, Fischer RL, Harada JJ, Goldberg RB. RASPBERRY3 gene encodes a novel protein important for embryo development. PLANT PHYSIOLOGY 2002; 129:691-705. [PMID: 12068112 PMCID: PMC161694 DOI: 10.1104/pp.004010] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2002] [Revised: 03/10/2002] [Accepted: 03/19/2002] [Indexed: 05/20/2023]
Abstract
We identified a new gene that is interrupted by T-DNA in an Arabidopsis embryo mutant called raspberry3. raspberry3 has "raspberry-like" cellular protuberances with an enlarged suspensor characteristic of other raspberry embryo mutants, and is arrested morphologically at the globular stage of embryo development. The predicted RASPBERRY3 protein has domains found in proteins present in prokaryotes and algae chloroplasts. Computer prediction analysis suggests that the RASPBERRY3protein may be localized in the chloroplast. Complementation analysis supports the possibility that the RASPBERRY3 protein may be involved in chloroplast development. Our experiments demonstrate the important role of the chloroplast, directly or indirectly, in embryo morphogenesis and development.
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MESH Headings
- Amino Acid Sequence
- Arabidopsis/genetics
- Arabidopsis/growth & development
- Arabidopsis Proteins/genetics
- Base Sequence
- Chloroplasts/genetics
- Cinnamates
- Cloning, Molecular
- Culture Techniques
- DNA, Bacterial/genetics
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- DNA, Complementary/isolation & purification
- DNA, Plant/chemistry
- DNA, Plant/genetics
- Genetic Complementation Test
- Hygromycin B/analogs & derivatives
- Hygromycin B/pharmacology
- Kanamycin/pharmacology
- Molecular Sequence Data
- Mutation
- Plant Leaves/genetics
- Plants, Genetically Modified
- Plasmids/genetics
- Seeds/genetics
- Seeds/growth & development
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
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Affiliation(s)
- Nestor R Apuya
- Department of Plant and Microbial Biology, University of California-Berkeley, Berkeley, CA 94720, USA
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9
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Fitzpatrick LM, Keegstra K. A method for isolating a high yield of Arabidopsis chloroplasts capable of efficient import of precursor proteins. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2001; 27:59-65. [PMID: 11489183 DOI: 10.1046/j.0960-7412.2001.01061.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Chloroplasts were isolated from Arabidopsis plants grown under different conditions, and using different protocols, to determine a method that would yield chloroplasts capable of binding and importing precursor proteins. Chloroplasts isolated from protoplasts and purified on a Percoll gradient were highly import-competent, with little non-specific binding of the precursor, and a high yield of intact chloroplasts (0.1 mg chlorophyll/g FW). Chloroplasts from plants grown on agar plates had a much higher rate of import than those from plants grown on soil. Protein import remained high at all of the ages tested for chloroplasts from plate-grown plants, whereas it declined during the development of soil-grown plants. Arabidopsis chloroplasts imported a range of precursor proteins and had nucleotide requirements for binding and import similar to those reported for pea chloroplasts.
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Affiliation(s)
- L M Fitzpatrick
- MSU-Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824-1312, USA
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10
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Richter S, Lamppa GK. Stromal processing peptidase binds transit peptides and initiates their ATP-dependent turnover in chloroplasts. J Cell Biol 1999; 147:33-44. [PMID: 10508853 PMCID: PMC2164977 DOI: 10.1083/jcb.147.1.33] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A stromal processing peptidase (SPP) cleaves a broad range of precursors targeted to the chloroplast, yielding proteins for numerous biosynthetic pathways in different compartments. SPP contains a signature zinc-binding motif, His-X-X-Glu-His, that places it in a metallopeptidase family which includes the mitochondrial processing peptidase. Here, we have investigated the mechanism of cleavage by SPP, a late, yet key event in the import pathway. Recombinant SPP removed the transit peptide from a variety of precursors in a single endoproteolytic step. Whereas the mature protein was immediately released, the transit peptide remained bound to SPP. SPP converted the transit peptide to a subfragment form that it no longer recognized. We conclude that SPP contains a specific binding site for the transit peptide and additional proteolysis by SPP triggers its release. A stable interaction between SPP and an intact transit peptide was directly demonstrated using a newly developed binding assay. Unlike recombinant SPP, a chloroplast extract rapidly degraded both the transit peptide and subfragment. A new degradative activity, distinguishable from SPP, was identified that is ATP- and metal-dependent. Our results indicate a regulated sequence of events as SPP functions during precursor import, and demonstrate a previously unrecognized ATP-requirement for transit peptide turnover.
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Affiliation(s)
- Stefan Richter
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637
| | - Gayle K. Lamppa
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637
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11
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Krimm I, Gans P, Hernandez JF, Arlaud GJ, Lancelin JM. A coil-helix instead of a helix-coil motif can be induced in a chloroplast transit peptide from Chlamydomonas reinhardtii. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 265:171-80. [PMID: 10491171 DOI: 10.1046/j.1432-1327.1999.00701.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A synthetic peptide MQVTMKSSAVSGQRVGGARVATRSVRRAQLQV corresponding to the 32 amino acid chloroplast transit sequence of the ribulose bisphosphatase carboxylase/oxygenase activase preprotein from Chlamydomonas reinhardtii, required for translocation through the envelope of the chloroplast, has been characterized structurally using CD and NMR under the same experimental conditions as used previously for the 32 amino acid presequence of preferredoxin from the same organism [Lancelin, J.-M., Bally, I., Arlaud, G. J., Blackledge, M., Gans, P., Stein, M. & Jacquot, J.-P. (1994) FEBS Lett. 343, 261-266]. The peptide is found to undergo a conformational transition in aqueous 2,2,2-trifluoroethanol, characterized by three turns of amphiphilic alpha-helix in the C-terminal region preceded by a disordered coil in the N-terminal region. Compared with the preferredoxin transit peptide, the helical and coiled domains are arranged in the reverse order along the peptide sequence, but the positively charged groups are distributed analogously as well as the hydrophobic residues within the amphiphilic alpha-helix. It is proposed that such coil-helix or helix-coil motifs, occasionally repeated, could be an intrinsic structural feature of chloroplastic transit peptides, adapted to the proper translocase and possibly to each nuclear-encoded chloroplast preproteins. This feature may distinguish chloroplastic transit sequences from the other organelle-targeting peptides in the eukaryotic green alga C. reinhardtii, particularly the mitochondrial transit sequences.
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Affiliation(s)
- I Krimm
- Laboratoire de RMN Biomoléculaire associé au CNRS, Université Claude Bernard-Lyon 1 and Ecole Supérieure de Chimie Physique et Electronique de Lyon, Villeurbanne, France
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12
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Richter S, Lamppa GK. A chloroplast processing enzyme functions as the general stromal processing peptidase. Proc Natl Acad Sci U S A 1998; 95:7463-8. [PMID: 9636172 PMCID: PMC22651 DOI: 10.1073/pnas.95.13.7463] [Citation(s) in RCA: 157] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A highly specific stromal processing activity is thought to cleave a large diversity of precursors targeted to the chloroplast, removing an N-terminal transit peptide. The identity of this key component of the import machinery has not been unequivocally established. We have previously characterized a chloroplast processing enzyme (CPE) that cleaves the precursor of the light-harvesting chlorophyll a/b binding protein of photosystem II (LHCPII). Here we report the overexpression of active CPE in Escherichia coli. Examination of the recombinant enzyme in vitro revealed that it cleaves not only preLHCPII, but also the precursors for an array of proteins essential for different reactions and destined for different compartments of the organelle. CPE also processes its own precursor in trans. Neither the recombinant CPE nor the native CPE of chloroplasts process a preLHCPII mutant with an altered cleavage site demonstrating that both forms of the enzyme are sensitive to the same structural modification of the substrate. The transit peptide of the precursor of ferredoxin is released by a single cleavage event and found intact after processing by recombinant CPE and a chloroplast extract as well. These results provide the first direct demonstration that CPE is the general stromal processing peptidase that acts as an endopeptidase. Significantly, recombinant CPE cleaves in the absence of other chloroplast proteins, and this activity depends on metal cations, such as zinc.
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Affiliation(s)
- S Richter
- Department of Molecular Genetics and Cell Biology, University of Chicago, 920 E. 58th Street, Chicago, IL 60637, USA
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13
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May T, Soll J. Positive charges determine the topology and functionality of the transmembrane domain in the chloroplastic outer envelope protein Toc34. J Cell Biol 1998; 141:895-904. [PMID: 9585409 PMCID: PMC2132774 DOI: 10.1083/jcb.141.4.895] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/1997] [Revised: 03/02/1998] [Indexed: 02/07/2023] Open
Abstract
The chloroplastic outer envelope protein Toc34 is inserted into the membrane by a COOH-terminal membrane anchor domain in the orientation Ncyto-Cin. The insertion is independent of ATP and a cleavable transit sequence. The cytosolic domain of Toc34 does not influence the insertion process and can be replaced by a different hydrophilic reporter peptide. Inversion of the COOH-terminal, 45-residue segment, including the membrane anchor domain (Toc34Cinv), resulted in an inverted topology of the protein, i.e., Nin-Ccyto. A mutual exchange of the charged amino acid residues NH2- and COOH-proximal of the hydrophobic alpha-helix indicates that a double-positive charge at the cytosolic side of the transmembrane alpha-helix is the sole determinant for its topology. When the inverted COOH-terminal segment was fused to the chloroplastic precursor of the ribulose-1,5-bisphosphate carboxylase small subunit (pS34Cinv), it engaged the transit sequence-dependent import pathway. The inverted peptide domain of Toc34 functions as a stop transfer signal and is released out of the outer envelope protein translocation machinery into the lipid phase. Simultaneously, the NH2-terminal part of the hybrid precursor remained engaged in the inner envelope protein translocon, which could be reversed by the removal of ATP, demonstrating that only an energy-dependent force but no further ionic interactions kept the precursor in the import machinery.
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Affiliation(s)
- T May
- Botanisches Institut, Christian-Albrechts-Universität Kiel, D-24118 Kiel, Germany
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14
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Kindle KL, Lawrence SD. Transit peptide mutations that impair in vitro and in vivo chloroplast protein import do not affect accumulation of the gamma-subunit of chloroplast ATPase. PLANT PHYSIOLOGY 1998; 116:1179-90. [PMID: 9501151 PMCID: PMC35088 DOI: 10.1104/pp.116.3.1179] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/1997] [Accepted: 11/21/1997] [Indexed: 05/18/2023]
Abstract
We have begun to take a genetic approach to study chloroplast protein import in Chlamydomonas reinhardtii by creating deletions in the transit peptide of the gamma-subunit of chloroplast ATPase-coupling factor 1 (CF1-gamma, encoded by AtpC) and testing their effects in vivo by transforming the altered genes into an atpC mutant, and in vitro by importing mutant precursors into isolated C. reinhardtii chloroplasts. Deletions that removed 20 or 23 amino acid residues from the center of the transit peptide reduced in vitro import to an undetectable level but did not affect CF1-gamma accumulation in vivo. The CF1-gamma transit peptide does have an in vivo stroma-targeting function, since chimeric genes in which the stroma-targeting domain of the plastocyanin transit peptide was replaced by the AtpC transit peptide-coding region allowed plastocyanin to accumulate in vivo. To determine whether the transit peptide deletions were impaired in in vivo stroma targeting, mutant and wild-type AtpC transit peptide-coding regions were fused to the bacterial ble gene, which confers bleomycin resistance. Although 25% of the wild-type fusion protein was associated with chloroplasts, proteins with transit peptide deletions remained almost entirely cytosolic. These results suggest that even severely impaired in vivo chloroplast protein import probably does not limit the accumulation of CF1-gamma.
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Affiliation(s)
- K L Kindle
- Plant Science Center, Biotechnology Program, 151 Biotechnology Building, Cornell University, Ithaca, New York 14853, USA.
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15
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Froehlich JE, Keegstra K. Identification of a translocation intermediate occupying functional protein import sites in the chloroplastic envelope membrane. J Biol Chem 1997; 272:8077-82. [PMID: 9065482 DOI: 10.1074/jbc.272.12.8077] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We used complexes of avidin and biotinylated precursors to generate translocation intermediates that occupy functional transport sites and thereby block the transport of other precursor proteins into pea chloroplasts. Cysteine residues of purified precursor to the small subunit of rubisco (prSS) were modified with the biotinylation reagent biotin-1-biotinamido-4-[-4'-(maleimidomethyl)-cyclohexane-ca rboxamido ]butane. Chemically biotinylated prSS was readily imported into chloroplasts. The addition of avidin, however, resulted in the formation of an avidin-biotinylated precursor complex that could not be imported into chloroplasts even when precursors had already engaged the transport apparatus before avidin was added. On fractionation, the avidin-biotinylated precursor complex associated with envelope membranes. Titration of transport sites with avidin-biotinylated precursor complexes revealed that saturation was reached at 2,000 molecules/chloroplast. Even with less than saturating levels of complexes, a sufficient number of translocation sites could be occupied with avidin-precursor complexes so that the import rate of freshly added radiolabeled prSS was reduced by 35%. From these observations we conclude that the trapped intermediates were blocking functional translocation sites. These biotinylated translocation intermediates should be useful in future efforts to purify and characterize the chloroplastic protein import machinery.
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Affiliation(s)
- J E Froehlich
- Michigan State University-DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48823-1312, USA.
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16
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Adam Z. Protein stability and degradation in chloroplasts. PLANT MOLECULAR BIOLOGY 1996; 32:773-783. [PMID: 8980530 DOI: 10.1007/bf00020476] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Affiliation(s)
- Z Adam
- Department of Agricultural Botany, Faculty of Agriculture, Hebrew University, Rehovot, Israel
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17
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Khrebtukova I, Spreitzer RJ. Elimination of the Chlamydomonas gene family that encodes the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase. Proc Natl Acad Sci U S A 1996; 93:13689-93. [PMID: 8942995 PMCID: PMC19392 DOI: 10.1073/pnas.93.24.13689] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Ribulose-1,5-bisphosphate carboxylase/ oxygenase (EC 4.1.1.39) is the key photosynthetic enzyme that catalyzes the first step of CO2 fixation. The chloroplast-localized holoenzyme of plants and green algae contains eight nuclear-encoded small subunits and eight chloroplast-encoded large subunits. Although much has been learned about the enzyme active site that resides within each large subunit, it has been difficult to assess the role of eukaryotic small subunits in holoenzyme function and expression. Small subunits are coded by a family of genes, precluding genetic screening or nuclear transformation approaches for the recovery of small-subunit mutants. In this study, the two small-subunit mutants. In this study, the two small-subunit genes of the green alga Chlamydomonas reinhardtii were eliminated during random insertional mutagenesis. The photosynthesis-deficient deletion mutant can be complemented with either of the two wild-type small-subunit genes or with a chimeric gene that contains features of both. Thus, either small subunit is sufficient for holoenzyme assembly and function. In the absence of small subunits, expression of chloroplast-encoded large subunits appears to be inhibited at the level of translation.
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Affiliation(s)
- I Khrebtukova
- Department of Biochemistry, University of Nebraska, Lincoln 68588-0664, USA
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Waegemann K, Soll J. Phosphorylation of the transit sequence of chloroplast precursor proteins. J Biol Chem 1996; 271:6545-54. [PMID: 8626459 DOI: 10.1074/jbc.271.11.6545] [Citation(s) in RCA: 155] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
A protein kinase was located in the cytosol of pea mesophyll cells. The protein kinase phosphorylates, in an ATP-dependent manner, chloroplast-destined precursor proteins but not precursor proteins, which are located to plant mitochondria or plant peroxisomes. The phosphorylation occurs on either serine or threonine residues, depending on the precursor protein used. We demonstrate the specific phosphorylation of the precursor forms of the chloroplast stroma proteins ferredoxin (preFd), small subunit of ribulose-bisphosphate-carboxylase (preSSU), the thylakoid localized light-harvesting chlorophyll a/b-binding protein (preLHCP), and the thylakoid lumen-localized proteins of the oxygen-evolving complex of 23 kDa (preOE23) and 33 kDa (preOE33). In the case of thylakoid lumen proteins which possess bipartite transit sequences, the phosphorylation occurs within the stroma-targeting domain. By using single amino acid substitution within the presequences of preSSU, preOE23, and preOE33, we were able to tentatively identify a consensus motif for the precursor protein protein kinase. This motif is (P/G)X(n)(R/K)X(n)(S/T)X(n) (S*/T*), were n = 0-3 amino acids spacer and S*/T* represents the phosphate acceptor. The precursor protein protein kinase is present only in plant extracts, e.g. wheat germ and pea, but not in a reticulocyte lysate. Protein import experiments into chloroplasts revealed that phosphorylated preSSU binds to the organelles, but dephosphorylation seems required to complete the translocation process and to obtain complete import. These results suggest that a precursor protein protein phosphatase is involved in chloroplast import and represents a so far unidentified component of the import machinery. In contrast to sucrose synthase, a cytosolic marker protein, the precursor protein protein kinase seems to adhere partially to the chloroplast surface. A phosphorylation-dephosphorylation cycle of chloroplast-destined precursor proteins might represent one step, which could lead to a specific sorting and productive translocation in plant cells.
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Affiliation(s)
- K Waegemann
- Botanisches Institut, Universitat Kiel, Germany
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Levy M, Adam Z. Mutations in the processing site of the precursor of ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit: effects on import, processing, assembly and stability. PLANT MOLECULAR BIOLOGY 1995; 29:53-61. [PMID: 7579167 DOI: 10.1007/bf00019118] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The small subunit (SSU) of Rubisco is synthesized in the cytosol in a precursor form. Upon import into the chloroplast, it is proteolytically processed at a Cys-Met bond to yield the mature form of the protein. To assess the importance of the Met residue for recognition and processing by the stromal peptidase, we substituted this residue with either Thr, Arg or Asp. The mutant precursor proteins were imported into isolated chloroplasts, and the products of the import reactions were analyzed. Mutants containing Thr or Arg residues at the putative processing site were processed to a single peptide, comigrating with the wild-type protein. N-terminal radio-sequencing revealed that these mutants were processed at the Cys-Thr and the Cys-Arg bond, respectively. After import of the Asp-containing mutant, four processed forms of the protein were observed. Analysis of the most abundant one, co-migrating with the wild-type protein, demonstrated that this species was also a product of correct processing, at the Cys-Asp bond. All the correctly processed peptides were found to be associated with the holoenzyme of Rubisco, and remained stable within the chloroplast, like the wild-type protein. The results of this study, together with previous ones, suggest that proper recognition and processing of the SSU precursor are more affected by residues N-terminal to the processing site than by the residue on the C-terminal side of this site.
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Affiliation(s)
- M Levy
- Department of Agricultural Botany, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel
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Serra EC, Krapp AR, Ottado J, Feldman MF, Ceccarelli EA, Carrillo N. The precursor of pea ferredoxin-NADP+ reductase synthesized in Escherichia coli contains bound FAD and is transported into chloroplasts. J Biol Chem 1995; 270:19930-5. [PMID: 7650008 DOI: 10.1074/jbc.270.34.19930] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The precursor of the chloroplast flavoprotein ferredoxin-NADP+ reductase from pea was expressed in Escherichia coli as a carboxyl-terminal fusion to glutathione S-transferase. The fused protein was soluble, and the precursor could be purified in a few steps involving affinity chromatography on glutathione-agarose, cleavage of the transferase portion by protease Xa, and ion exchange chromatography on DEAE-cellulose. The purified prereductase contained bound FAD but displayed marginally low levels of activity. Removal of the transit peptide by limited proteolysis rendered a functional protease-resistant core exhibiting enzymatic activity. The FAD-containing precursor expressed in E. coli was readily transported into isolated pea chloroplasts and was processed to the mature size, both inside the plastid and by incubation with stromal extracts in a plastid-free reaction. Import was dependent on the presence of ATP and was stimulated severalfold by the addition of plant leaf extracts.
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Affiliation(s)
- E C Serra
- Departamento de Ciencias Biológicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Argentina
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Pilon M, Wienk H, Sips W, de Swaaf M, Talboom I, van 't Hof R, de Korte-Kool G, Demel R, Weisbeek P, de Kruijff B. Functional domains of the ferredoxin transit sequence involved in chloroplast import. J Biol Chem 1995; 270:3882-93. [PMID: 7876133 DOI: 10.1074/jbc.270.8.3882] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
In order to analyze the information content of a chloroplast transit sequence, we have constructed and analyzed by in vitro assays seven substitution and 20 deletion mutants of the ferredoxin transit sequence. The N-terminal part and the C-terminal part are important for targeting, and in addition the C-terminal region is required for processing. A third region is important for translocation but not for the initial interaction with the envelope. A fourth region is less essential for in vitro import. Purified precursors were tested for their ability to compete for the in vitro import of radiolabeled wild-type precursor, which confirmed the important role in chloroplast recognition of both the N- and the C-terminal domain of the transit sequence. Monolayer experiments showed that the N terminus was mainly involved in the insertion into mono-galactolipid-containing lipid surfaces whereas the C terminus mediates the recognition of negatively charged lipids. A sequence comparison to other transit sequences suggests that the domain structure of the ferredoxin transit sequence can be extended to these sequences and thus reveals a general structural design of transit sequences.
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Affiliation(s)
- M Pilon
- Institute of Biomembranes, Utrecht University, The Netherlands
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