Double cache domain 1 covers the last three strands from the membrane distal PAS-like domain, the first two strands of the membrane proximal domain, and the connecting elements between the two domains [2]. This domain when present in chemoreceptors recognise several signals such as proteinogenic amino acids, GABA, Histamine and polyamines, decanoic acid, Autoinducer-2, purine derivatives, quaternary amines, citrate and taurine, among others. When associated with histidine kinases, it recognises C3/C4-dicarboxylic acids, Spermine, guanosine and Autoinducer-2 (Mantilla et al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1 https://doi.org/10.1093/femsre/fuab043).

1: Cache - a signaling domain common to animal Ca(2+)-channel subunits and a class of prokaryotic chemotaxis receptors. Anantharaman V, Aravind L; Trends Biochem Sci 2000;25:535-537. PMID:11084361

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