Figure 6. Overall reaction sequence for MsrB3.

Cartoon depicting a potential reaction sequence for MsrB3 (adapted from ref. [17]). Fully reduced enzyme (A) reacts with methionine sulfoxide (Met-O) to form methionine and in the process the active site cysteine 126 becomes sulfenylated (B). This sulfenylated thiol can then be reduced by either cys03 or cys09 forming a transient disulfide between the active site and the resolving thiol (C_i or C_ii). After disulfide exchange, an internal disulfide is formed between cys 03 and 09 (D). A second molecule of methionine sulfoxide can then react with the active site cysteine to form E. The internal disulfide can then be reduced to regenerate (B).