Double Cache domain 2 (dCache_2) may be a result of single Cache domain 2 (sCache_2) duplication [2].

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