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 Gramposi tive 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, c ontains motifs that are conserved amongst sensor histidine kinases, althoug h not in the same relative positions. In this study, the conserved histidin e residue (H255), the GXGL and DXGXG motifs, and two glutamate residues loc ated in putative transmembrane domains were altered by site-directed mutage nesis to examine their significance for VirS function. Introduction of the mutated virS genes into the virS::Tn916 mutant, JIR4000. showed that the al tered virS genes were not able to complement the host mutation. These resul ts demonstrate that the conserved motifs, including the cytoplasmic DXGXG m otif which is located between the putative transmembrane domains 4 and 5, a re functional. Furthermore, it is concluded that charged residues located w ithin two of these transmembrane domains are also required for the structur al or functional integrity of the VirS sensor kinase.