title: Two highly homologous methionine sulfoxide reductase A from tomato (Solanum lycopersicum), exhibit distinct catalytic properties.
abstract: E4, which is a fruit-ripening gene that is strongly induced by ethylene, has been reported to be a member of the methionine sulfoxide reductase A (MSRA) gene. In the present study, we determined for the first time the enzymatic activity and delineated the catalytic mechanism of the E4 protein via site-directed mutagenesis. The disulfide intermolecular cross-linking, kinetics parameter, thiol content titration analysis of wild-type and mutated E4 proteins revealed that the cysteine at position 37 (Cys-37) was the key catalytic residue, and Cys-194, but not Cys-180 served as the first recycling Cys in the thioredoxin (Trx)-dependent regeneration system. In addition, the SlMSRA2 protein, which was encoded by another MSRA gene, shared high similarity with the E4 protein and was truncated at the C-terminus. The wild-type and mutated SlMSRA2 enzymes had similar activities compared to the E4 protein using DTT as a reductant, but showed extremely low activities in the Trx-dependent reduction system. Our results indicated that E4 and SlMSRA2 proteins might exhibit distinct catalytic mechanisms.
authors.affiliation: Department of Medical Biotechnology, College of Biomedical Science, Kangwon National University, Chuncheon, Gangwon-do, South Korea.
authors.forename: Changbo
authors.initials: C
authors.lastname: Dai
authors.forename: Woong
authors.initials: W
authors.lastname: Han
authors.forename: Myeong-Hyeon
authors.initials: MH
authors.lastname: Wang
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D007700:Kinetics; D018551:Solanum lycopersicum / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D051150:Methionine Sulfoxide Reductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D010940:Plant Proteins; D051150:Methionine Sulfoxide Reductases