Cache domain
In molecular biology, the cache domain is an extracellular protein domain that is predicted to have a role in small-molecule recognition in a wide range of proteins, including the animal dihydropyridine-sensitive voltage-gated Ca2+ channel alpha-2delta subunit, and various bacterial chemotaxis receptors. The name Cache comes from CAlcium channels and CHEmotaxis receptors. This domain consists of an N-terminal part with three predicted strands and an alpha-helix, and a C-terminal part with a strand dyad followed by a relatively unstructured region. The N-terminal portion of the (unpermuted) Cache domain contains three predicted  strands that could form a sheet analogous to that present in the core of the PAS domain structure. Cache domains are particularly widespread in bacteria such as "Vibrio cholerae". The animal calcium channel alpha-2delta subunits might have acquired a part of their extracellular domains from a bacterial source. The Cache domain appears to have arisen from the GAF-PAS fold despite their divergent functions.