The Rhodobacter sphaeroides methionine sulfoxide reductase MsrP can reduce R- and S-diastereomers of methionine sulfoxide from a broad-spectrum of protein substrates

Methionine (Met) is prone to oxidation and can be converted to Met sulfoxide (MetO), which exists as R- and S-diastereomers. MetO can be reduced back to Met by the ubiquitous methionine sulfoxide reductase (Msr) enzymes. Canonical MsrA and MsrB were shown as absolutely stereospecific for the reduction of S- and R-diastereomer, respectively. Recently, the molybdenum-containing protein MsrP, conserved in all gram-negative bacteria, was shown to be able to reduce MetO of periplasmic proteins without apparent stereospecificity in Escherichia coli. Here, we describe the substrate specificity of the Rhodobacter sphaeroides MsrP. Proteomics analysis coupled to enzymology approaches indicate that it reduces a broad spectrum of periplasmic oxidized proteins. Moreover, using model proteins, we demonstrated that RsMsrP preferentially reduces unfolded oxidized proteins and we confirmed that this enzyme, like its E. coli homolog, can reduce both R- and S -diastereomers of MetO with similar efficiency.