Structural Basis of a Thiol-Disulfide Oxidoreductase in the Hedgehog-Forming Actinobacterium Corynebacterium matruchotii.

The actinobacterium has been implicated in nucleation of oral microbial consortia leading to biofilm formation. Due to the lack of genetic tools, little is known about basic cellular processes, including protein secretion and folding, in this organism. We report here a survey of the genome, which encodes a large number of exported proteins containing paired cysteine residues, and identified an oxidoreductase that is highly homologous to the thiol-disulfide oxidoreductase MdbA (MdbA). Crystallization studies uncovered that the 1.2-Å resolution structure of MdbA (MdbA) possesses two conserved features found in actinobacterial MdbA enzymes, a thioredoxin-like fold and an extended α-helical domain. By reconstituting the disulfide bond-forming machine , we demonstrated that MdbA catalyzes disulfide bond formation within the actinobacterial pilin FimA. A new gene deletion method supported that is essential in Remarkably, heterologous expression of MdbA in the Δ mutant rescued its known defects in cell growth and morphology, toxin production, and pilus assembly, and this thiol-disulfide oxidoreductase activity required the catalytic motif CXXC. Altogether, the results suggest that MdbA is a major thiol-disulfide oxidoreductase, which likely mediates posttranslocational protein folding in by a mechanism that is conserved in The actinobacterium has been implicated in the development of oral biofilms or dental plaque; however, little is known about the basic cellular processes in this organism. We report here a high-resolution structure of a oxidoreductase that is highly homologous to the thiol-disulfide oxidoreductase MdbA. By biochemical analysis, we demonstrated that MdbA catalyzes disulfide bond formation Furthermore, a new gene deletion method revealed that deletion of is lethal in Remarkably, MdbA can replace MdbA to maintain normal cell growth and morphology, toxin production, and pilus assembly. Overall, our studies support the hypothesis that utilizes MdbA as a major oxidoreductase to catalyze oxidative protein folding.