ligand binding sensor domain of Tar- and Tsr-related chemoreceptors
Escherichia coli Tar (taxis to aspartate and repellents) and Tsr (taxis to serine and repellents) are homologous transmembrane chemoreceptors that have a high specificity for aspartate and serine, respectively. Both are homodimeric receptors and contain an N-terminal periplasmic ligand binding domain, a transmembrane region, a HAMP domain and a C-terminal cytosolic signaling domain. E. coli Tar mediates bacterial chemotaxis toward attractants, including aspartate (Asp) and maltose, and away from repellents such as nickel and cobalt ions. Tsr has many roles, including sensing of external (serine, leucine) and internal (pH) environments. In Salmonella enterica serovar Typhimurium, Tsr, also called methyl-accepting chemotaxis protein (MCP), is involved in sensing host-derived nitrate in murine intestinal epithelium, thus contributing to invasion of Peyer's patches. This model represents the ligand binding domain of Tar and Tsr.
Jiyao W et al.(2023). "The conserved domain database in 2023.",