Structure of BrxA from Staphylococcus aureus, a bacilliredoxin involved in redox homeostasis in Firmicutes.

Bacilliredoxins are small proteins that are involved in redox homeostasis in bacillithiol-producing bacteria. They reduce mixed bacillithiol disulfides on protected proteins through a disulfide-exchange reaction, restoring the thiol group on the target protein. Bacilliredoxins contain an unusual conserved CGC motif, and their exact catalytic mechanism remains unclear. Here, a 1.6 Å resolution X-ray crystallographic structure of the bacilliredoxin BrxA (YphP) from Staphylococcus aureus is presented. The structure contains bacillithiol in a mixed disulfide with Cys54, as well as a disulfide linkage at Cys56, which may play a role in dimer stabilization. The structure presented here will provide insight into the function of BrxA and other bacilliredoxins.