The Bacillus subtilis YkuV is a thiol:disulfide oxidoreductase revealed by its redox structures and activity

The Bacillus subtilis YkuV responds to environmental oxidative stress and plays an important role for the bacteria to adapt to the environment. Bioinformatic analysis suggests that YkuV is a homolog of membrane-anchored proteins and belongs to the thioredoxin-like protein superfamily containing the typical Cys-Xaa-Xaa-Cys active motif. However, the biological function of this protein remains unknown thus far. In order to elucidate the biological function, we have determined the solution structures of both the oxidized and reduced forms of B. subtilis YkuV by NMR spectroscopy and performed biochemical studies. Our results demonstrated that the reduced YkuV has a low midpoint redox potential, allowing it to reduce a variety of protein substrates. The overall structures of both oxidized and reduced forms are similar, with a typical thioredoxin-like fold. However, significant conformational changes in the Cys-Xaa-Xaa-Cys active motif of the tertiary structures are observed between the two forms. In addition, the backbone dynamics provide further insights in understanding the strong redox potential of the reduced YkuV. Furthermore, we demonstrated that YkuV is able to reduce different protein substrates in vitro. Together, our results clearly established that YkuV may function as a general thiol:disulfide oxidoreductase, which acts as an alternative for thioredoxin or thioredoxin reductase to maintain the reducing environment in the cell cytoplasm.