Two highly homologous methionine sulfoxide reductase A from tomato (Solanum lycopersicum), exhibit distinct catalytic properties

Protein J. 2012 Apr;31(4):285-92. doi: 10.1007/s10930-012-9403-z.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Catalysis
  • Kinetics
  • Lycopersicon esculentum / chemistry
  • Lycopersicon esculentum / enzymology*
  • Lycopersicon esculentum / genetics
  • Methionine Sulfoxide Reductases / chemistry*
  • Methionine Sulfoxide Reductases / genetics
  • Methionine Sulfoxide Reductases / metabolism
  • Molecular Sequence Data
  • Plant Proteins / chemistry*
  • Plant Proteins / genetics
  • Plant Proteins / metabolism
  • Sequence Alignment

Substances

  • Plant Proteins
  • Methionine Sulfoxide Reductases