InterPro domain: IPR029070

This superfamily represents the chitinase insertion domain (CID) that is found in chitinases or chitinase-like proteins. It is composed of five or six anti-parallel beta-strands and one alpha-helix and it inserts between the seventh alpha-helix and seventh beta-strand of the TIM barrel [ 1 ]. The CID domain forms a wall alongside the TIM barrel substrate-binding cleft of chitinase which increases the depth of the cleft. Family 18 chitinases (also known as glycosyl hydrolase 18 family) can be classified into three subfamilies: A, B, and C. The CID domain can be found in the subfamily A, but is absent in the subfamily B [ 2 ].

Some mammalian glycoproteins with various functions also consist of a TIM domain and a CID domain, such as human cartilage glycoprotein-39 (HCgp-39), also known as chitinase-3-like protein 1 [ 2 ].

1. Sequence and structural analysis of the chitinase insertion domain reveals two conserved motifs involved in chitin-binding. PLoS ONE 5, e8654