Glutamate residues in the putative transmembrane region are required for the function of the VirS sensor histidine kinase from Clostridium perfringens

The causative agent of gas gangrene, Clostridium perfringens. is a Grampositive anaerobe which produces a number of extracellular toxins and enzymes. The production of several of these toxins is regulated by the VirS/NirR two-component signal transduction system. The sensor histidine kinase, VirS, contains motifs that are conserved amongst sensor histidine kinases, although not in the same relative positions. In this study, the conserved histidine residue (H255), the GXGL and DXGXG motifs, and two glutamate residues located in putative transmembrane domains were altered by site-directed mutagenesis to examine their significance for VirS function. Introduction of the mutated virS genes into the virS::Tn916 mutant, JIR4000. showed that the altered virS genes were not able to complement the host mutation. These results demonstrate that the conserved motifs, including the cytoplasmic DXGXG motif which is located between the putative transmembrane domains 4 and 5, are functional. Furthermore, it is concluded that charged residues located within two of these transmembrane domains are also required for the structural or functional integrity of the VirS sensor kinase.