Characterization of a novel methionine sulfoxide reductase A from tomato (Solanum lycopersicum ), and its protecting role in Escherichia coli.

Methionine sulfoxide reductase A (MSRA) is a ubiquitous enzyme that has been demonstrated to reduce the S enantiomer of methionine sulfoxide (MetSO) to methionine (Met) and can protect cells against oxidative damage. In this study, we isolated a novel MSRA (SIMSRA2) from Micro-Tom (Solanum lycopersicum L cv. Micro-Tom) and characterized it by subcloning the coding sequence into a pET expression system. Purified recombinant protein was assayed by HPLC after expression and refolding. This analysis revealed the absolute specificity for methionine-S-sulfoxide and the enzyme was able to convert both free and protein-bound MetSO to Met in the presence of DTI. In addition, the optimal pH, appropriate temperature, and K-m and K-cat values for MSRA2 were observed as 8.5, 25 degrees C, 352 +/- 25 mu M, and 0.066 +/- 0.009 S-1, respectively. Disk inhibition and growth rate assays indicated that SIMSRA2 may play an essential function in protecting E. coli against oxidative damage. [BMB reports 2011; 44(12): 805-810]