Characterization of a methionine sulfoxide reductase B from tomato (Solanum lycopersicum), and its protecting role in Saccharomyces cerevisiae.

In the present study, we isolated a methionine sulfoxide reductase B gene, termed SlMSRB1, from tomato (Solanum lycopersicum). In the organ-specific analysis, high expression levels of SlMSRB1 were detected in red mature fruits, leaves and flowers while low transcriptional levels of SlMSRB1 mRNA were observed in stems and roots. In the green fluorescence analysis of SlMSRB1- overexpressed Arabidopsis, signal corresponding to SlMSRB1 was merely detected in chloroplast, suggesting that tomato MSRB1 is a chloroplastial localization protein. Substrate specificity analysis of recombinant SlMSRB1 showed that the enzyme was only targeted to the R epimer of methionine sulfoxide (MetSO) and was able to convert both free and protein-bound MetSO back to methionine in the presence of dithithreitol (DTT). In addition, SlMSRB1 exhibited no activity in thioredoxin dependent system or the substitution of cysteine at position 181 in the DTT-dependent reduction system. Finally, overexpression of SlMSRB1 in yeast revealed that the SlMSRB1 gene might play a critical role in protecting Saccharomyces cerevisiae against oxidative stress.