Proteomic Characterization of the Chlamydomonas reinhardtii Chloroplast Ribosome

摘要

We have conducted a proteomic analysis of the 70 S ribosome from the Chlamydomonas reinhardtii chloroplast. Twenty-seven orthologs of Escherichia coli large subunit proteins were identified in the 50 S subunit, as well as an ortholog of the spinach plastid-specific ribosomal protein-6. Several of the large subunit proteins of C. reinhardtii have short extension or insertion sequences, but overall the large subunit proteins are very similar to those of spinach chloroplast and E. coli. Two proteins of 38 and 41 kDa, designated RAP38 and RAP41, were identified from the 70 S ribosome that were not found in either of the ribosomal subunits. Phylogenetic analysis identified RAP38 and RAP41 as paralogs of spinach CSP41, a chloroplast RNA-binding protein with endoribonuclease activity. Overall, the chloroplast ribosome of C. reinhardtii is similar to those of spinach chloroplast and E. coli, but the C. reinhardtii ribosome has proteins associated with the 70 S complex that are related to non-ribosomal proteins in other species. In addition, the 30 S subunit contains unusually large orthologs of E. coli S2, S3, and S5 and a novel S1-type protein (Yamaguchi, K. et al., (2002) Plant Cell 14, 2957–2974). These additional proteins and domains likely confer functions used to regulate chloroplast translation in C. reinhardtii. We have conducted a proteomic analysis of the 70 S ribosome from the Chlamydomonas reinhardtii chloroplast. Twenty-seven orthologs of Escherichia coli large subunit proteins were identified in the 50 S subunit, as well as an ortholog of the spinach plastid-specific ribosomal protein-6. Several of the large subunit proteins of C. reinhardtii have short extension or insertion sequences, but overall the large subunit proteins are very similar to those of spinach chloroplast and E. coli. Two proteins of 38 and 41 kDa, designated RAP38 and RAP41, were identified from the 70 S ribosome that were not found in either of the ribosomal subunits. Phylogenetic analysis identified RAP38 and RAP41 as paralogs of spinach CSP41, a chloroplast RNA-binding protein with endoribonuclease activity. Overall, the chloroplast ribosome of C. reinhardtii is similar to those of spinach chloroplast and E. coli, but the C. reinhardtii ribosome has proteins associated with the 70 S complex that are related to non-ribosomal proteins in other species. In addition, the 30 S subunit contains unusually large orthologs of E. coli S2, S3, and S5 and a novel S1-type protein (Yamaguchi, K. et al., (2002) Plant Cell 14, 2957–2974). These additional proteins and domains likely confer functions used to regulate chloroplast translation in C. reinhardtii. In the chloroplast, where proteins of the photosynthetic apparatus and the carbon-fixing enzymes are synthesized, gene expression is primarily regulated during translation (1Mayfield S.P. Yohn C.B. Cohen A. Danon A. Annu. Rev. Plant Physiol. Plant Mol. Biol. 1995; 46: 147-166Crossref Scopus (159) Google Scholar). Chloroplast translation has been thought to be similar to translation in bacterial systems, mainly because of similarities in ribosomal RNA and the sensitivity of chloroplast ribosomes to bacterial antibiotics. These similarities support the endosymbiotic theory that chloroplasts originated from a photosynthetic prokaryote, cyanobacteria (2Bogorad L. Science. 1975; 188: 891-898Crossref PubMed Scopus (108) Google Scholar, 3Gray M.W. Int. Rev. Cytol. 1992; 141: 233-357Crossref PubMed Scopus (441) Google Scholar). It is now recognized that chloroplast gene expression and chloroplast translation are unique and quite different from bacterial systems (1Mayfield S.P. Yohn C.B. Cohen A. Danon A. Annu. Rev. Plant Physiol. Plant Mol. Biol. 1995; 46: 147-166Crossref Scopus (159) Google Scholar, 4Harris E.H. Boynton J.E. Gillham N.W. Microbiol. Rev. 1994; 58: 700-754Crossref PubMed Google Scholar, 5Yamaguchi K. von Knoblauch K. Subramanian A.R. J. Biol. Chem. 2000; 275: 28455-28465Abstract Full Text Full Text PDF