REP27, a Tetratricopeptide Repeat Nuclear-Encoded and Chloroplast-Localized Protein, Functions in D1/32-kD Reaction Center Protein Turnover and Photosystem II Repair from Photodamage

• Published in: Plant physiology (Bethesda) 2007-04, Vol.143 (4), p.1547-1560
• Main Authors: Park, Sungsoon, Khamai, Phichaya, Garcia-Cerdan, Jose Gines, Melis, Anastasios
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Base Sequence; Biological and medical sciences; Cell Nucleus - metabolism; Chlamydomonas reinhardtii; Chloroplasts - metabolism; DNA Primers; DNA, Plant; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Genes, Plant; Light; Metabolism; Molecular Sequence Data; Photosynthesis, respiration. Anabolism, catabolism; Photosystem II Protein Complex - metabolism; Plant physiology and development; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - metabolism; Plasmids; Protein Biosynthesis; Sequence Homology, Amino Acid; Transcription, Genetic
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.107.096396

The goal of this research is elucidation of the molecular mechanism for the unique photosystem II (PSII) damage and repair cycle in chloroplasts. A frequently occurring, irreversible photooxidative damage inhibits the PSII charge separation reaction and stops photosynthesis. The chloroplast PSII repair process rectifies this adverse effect by selectively removing and replacing the photoinactivated D1/32-kD reaction center protein (the chloroplast-encoded psbA gene product) from the massive (>1,000 kD) water-oxidizing and O₂-evolving PSII holocomplex. DNA insertional mutagenesis in the model organism Chlamydomonas reinhardtii was applied for the isolation and characterization of rep27, a repair-aberrant mutant. Gene cloning and biochemical analyses in this mutant resulted in the identification of REP27, a nuclear gene encoding a putative chloroplast-targeted protein, which is specifically required for the completion of the D1 turnover process but is not essential for the de novo biogenesis and assembly of the PSII holocomplex in this model green alga. The REP27 protein contains two highly conserved tetratricopeptide repeats, postulated to facilitate the psbA mRNA cotranslational insertion of the nascent D1 protein in the existing PSII core template. Elucidation of the PSII repair mechanism may reveal the occurrence of hitherto unknown regulatory and catalytic reactions for the selective in situ replacement of specific proteins from within multiprotein complexes.