Characterisation of the periplasmic methionine sulfoxide reductase (MsrP) from Salmonella Typhimurium.

The oxidation of free methionine (Met) and Met residues inside proteins leads to the formation of methionine sulfoxide (Met-O). The reduction of Met-O to Met is catalysed by a ubiquitous enzyme family: the methionine sulfoxide reductases (Msr). The importance of Msr systems in bacterial physiology and virulence has been reported in many species. Salmonella Typhimurium, a facultative intracellular pathogen, contains four cytoplasmic Msr. Recently, a periplasmic Msr enzyme (MsrP) has been identified in Escherichia coli. In the present study, the STM14_4072 gene from Salmonella was shown to encode the MsrP protein (StMsrP). We describe the experimental procedure and precautions for the production of this molybdo-enzyme. StMsrP was also demonstrated to reduce free Met-O and to catalyse the complete repair of an oxidized protein. More importantly, this study provides for the first time access to the exhaustive list of the Msr systems of a pathogen, including four cytoplasmic enzymes (MsrA, MsrB, MsrC, BisC) and one periplasmic enzyme (MsrP).