Unveiling the enigmatic traits of Corynebacterium glutamicum mycoredoxin-3: A tiny redox protein displaying swapped homodimer formation and DsbA-like oxidase activity

Mycoredoxins (Mrxs) are a group of small dithiol oxidoreductases that share a conserved CXXC active site sequence motif resembling glutaredoxins. They are commonly found in saprophytic microorganisms, including Actinobacteria such as Mycobacterium tuberculosis. Among the known mycoredoxins, Corynebacterium glutamicum (Cg) Mrx1, featuring a conserved CVQC active site, functions as a mycothiol-dependent monothiol oxidoreductase. On the other hand, Mrx2, also known as NrdH-redoxin and containing the same CVQC motif, exhibits dithiol oxidoreductase properties and receives electrons from thioredoxin reductase (TrxR). Recently, it has been reported that CgMrx3, featuring a CGSC motif, acts as a thioredoxin, although its structural and biophysical characteristics remain unexplored.