Structural and functional diversity of sensor domains in bacterial transmembrane receptors

The ability of bacteria to adapt to changing environmental conditions largely depends on transmembrane receptors that sense signal molecules and generate responses such as chemotaxis, changes in gene expression, or alterations in second-messenger levels. Although these receptors differ significantly in function, they share a common mode of activation that involves signal molecule interaction with sensor domains. A major challenge in microbiology lies in the limited knowledge of ligands that stimulate receptors. Here, we review recent advances in this field, including the occurrence of multi-modular sensor domains, the identification of co-component signal transduction systems, evidence for sensor domain evolution from transporters, and the use of binding pocket sequence motifs to identify sensor domain ligands.