The HBM domain: introducing bimodularity to bacterial sensing.

We have recently reported the three dimensional structure of the McpS chemoreceptor sensor domain in complex with its cognate ligands. The domain was characterized by a bimodular architecture, where ligand binding to each module caused a chemotactic response. This is a novel small molecule binding domain, which, however, is un-annotated in relevant databases. We report here the domain signature of the family of McpS-like sensor domains, which was termed helical bimodular (HBM) domain. The HBM domain was identified in Bacteria and Archaea and forms part of chemoreceptors and histidine kinases. The conservation of amino acids in the ligand binding sites of both modules suggests that HBM family members recognize similar ligands.