Andrzej Joachimiak, Melissa Reardon-Robinson, Hung Ton-That, Jerzy Osipiuk, Reyhaneh Tirgar, Truc Thanh Luong
The actinobacteriumCorynebacterium matruchotiihas 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 theC. matruchotiigenome, which encodes a large number of exported proteins containing paired cysteine residues, and identified an oxidoreductase that is highly homologous to theCorynebacterium diphtheriaethiol-disulfide oxidoreductase MdbA (MdbACd). Crystallization studies uncovered that the 1.2-Å resolution structure ofC. matruchotiiMdbA (MdbACm) conforms two conserved features found in actinobacterial MdbA enzymes, a thioredoxin-like fold and an extended α-helical domain. By reconstituting disulfide bond-forming machinein vitro, we demonstrated that MdbACmcatalyzes disulfide bond formation within the actinobacterial pilin FimA. A new gene deletion method supported thatmdbAis essential inC. matruchotiiRemarkably, heterologous expression of MdbACmin theCdiphtheriaeΔmdbAmutant 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 MdbACmis a major thiol-disulfide oxidoreductase, which likely mediates post-translocational protein folding inC. matruchotiiby a mechanism that is conserved in Actinobacteria.IMPORTANCEThe actinobacteriumCorynebacterium matruchotiihas 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 aC. matruchotiioxidoreductase that is highly homologous to theCorynebacterium diphtheriaethiol-disulfide oxidoreductase MdbA. By biochemical analysis, we demonstrated thatC. matruchotiiMdbA catalyzes disulfide bond formationin vitroFurthermore, a new gene deletion method revealed that deletion ofmdbAis lethal inC. matruchotiiRemarkably,C. matruchotiiMdbA can substituteC. diphtheriaeMdbA to maintain normal cell growth and morphology, toxin production, and pilus assembly. Overall, our studies support thatC. matruchotiiutilizes MdbA as a major oxidoreductase to catalyze oxidative protein folding.
