MsrB, also known as, methionine sulfoxide reductase B from Escherichia coli, belongs to the msrB Met sulfoxide reductase family. E.coli msrB carries out the reduction of methionine-R-sulfoxide to methionine. This protein possess a metal binding site composed of two CXXC motifs. The bound metal (zinc or iron) may stabilize the conformation of the enzymes.