first PDC (PhoQ/DcuS/CitA) domain of methyl-accepting chemotaxis proteins, diguanylate-cyclase and similar domains
Histidine kinase (HK) receptors are part of two-component systems (TCS) in bacteria that play a critical role for sensing and adapting to environmental changes. Typically, HK receptors contain an extracellular sensing domain flanked by two transmembrane helices, an intracellular dimerization histidine phosphorylation domain (DHp), and a C-terminal kinase domain, with many variations on this theme. HK receptors in this family contain double PDC (PhoQ/DcuS/CitA) sensor domains. Signals detected by the sensor domain are transmitted through DHp to the kinase domain, resulting in the phosphorylation of a conserved histidine residue in DHp; phosphotransfer to a conserved aspartate in its cognate response regulator (RR) follows, which leads to the activation of genes for downstream cellular responses. The HK family includes not just histidine kinase receptors but also sensors for chemotaxis proteins and diguanylate cyclase receptors, implying a combinatorial molecular evolution.
Jiyao W et al.(2023). "The conserved domain database in 2023.",