Cache_3 is the periplasmic sensor domains of sensor histidine kinase of E. coli DcuS. This domain forms one of the components of the two-component signalling system that allows bacteria to adapt to changing environments. The ability of bacteria to monitor and adapt to their environment is crucial to their survival, and two-component signal transduction systems mediate most of these adaptive responses. One component is a histidine kinase sensor - this domain - most commonly part of a homodimeric transmembrane sensor protein, and the second component is a cytoplasmic response regulator. The two components interact in tandem through a phospho-transfer cascade [1].

1: Crystal structures of C4-dicarboxylate ligand complexes with sensor domains of histidine kinases DcuS and DctB. Cheung J, Hendrickson WA; J Biol Chem. 2008;283:30256-30265. PMID:18701447

2: Cache Domains That are Homologous to, but Different from PAS Domains Comprise the Largest Superfamily of Extracellular Sensors in Prokaryotes. Upadhyay AA, Fleetwood AD, Adebali O, Finn RD, Zhulin IB; PLoS Comput Biol. 2016;12:e1004862. PMID:27049771