In molecular biology, the CBS domain is a protein domain found in a range of proteins in all species from bacteria to humans. It was first identified as a conserved sequence region in 1997 and named after cystathionine beta synthase, one of the proteins it is found in. CBS domains are also found in a wide variety of other proteins such as inosine monophosphate dehydrogenase,voltage gated chloride channels and AMP-activated protein kinase (AMPK). CBS domains regulate the activity of associated enzymatic and transporter domains in response to binding molecules with adenosyl groups such as AMP and ATP, or s-adenosylmethionine.

The CBS domain is composed of a beta-alpha-beta-beta-alpha secondary structure pattern that is folded into a globular tertiary structure that contains a three-stranded antiparallel β-sheet with two α-helices on one side. CBS domains are always found in pairs in protein sequences and each pair of these domains tightly associate in a pseudo dimeric arrangement through their β-sheets forming a so-called CBS-pair or Bateman domain. These CBS domain pairs can associate in a head-to-head (i.e. PDB codes, 3KPC, 1PVM, 2OOX) or a head-to-tail (i.e. PDB codes 1O50, 1PBJ) manner forming a disk-like compact structure. By doing so, they form clefts that constitute the canonical ligand binding regions. In principle, the number of canonical binding sites matches the number of CBS domains within the molecule and are traditionally numbered according to the CBS domain that contains each of the conserved aspartate residues that potentially interact with the ribose of the nucleotides. However, not all of these cavities might necessarily bind nucleotides or be functional. Recently, a non-canonical site for AMP has also been described in protein MJ1225 from M. jannaschii, though its functional role is still unknown.

...
Wikipedia