The 'CABIT' domain (for 'cysteine-containing, all- in Themis') is found in a newly identified gene family that has three mammalian homologues (Themis, Icb1 and 9130404H23Rik) that encode proteins with two CABIT domains and a highly conserved proline-rich region. In contrast, Fam59A, Fam59B and related proteins from mammals to cnidarians, including the insect Serrano proteins, have a single copy of the CABIT domain, a proline-rich region and often a C-terminal SAM (sterile-motif) domain. Multiple-sequence alignment has predicted that the CABIT domain adopts an all-strand structure with at least 12 strands, ie a dyad of six-stranded beta-barrel units. The CABIT domain contains a nearly absolutely conserved cysteine residue which is likely to be central to its function. CABIT domain proteins function downstream of tyrosine kinase signalling and interact with GRB2.

1: Themis is a member of a new metazoan gene family and is required for the completion of thymocyte positive selection. Johnson AL, Aravind L, Shulzhenko N, Morgun A, Choi SY, Crockford TL, Lambe T, Domaschenz H, Kucharska EM, Zheng L, Vinuesa CG, Lenardo MJ, Goodnow CC, Cornall RJ, Schwartz RH; Nat Immunol. 2009;10:831-839. PMID:19597497