This is a C-terminal domain found in CAS family members. The CAS (Crk-Associated Substrate) protein family is a group of scaffolding proteins that play important modulatory roles in both normal and pathological cell growth regulation. They contain an N-terminal Src homology 3 (SH3) domain Pfam:PF00018 and a substrate domain (SD). The SD contains a large number of YxxP motifs, which when phosphorylated by Src-family kinases provide canonical binding sites for proteins containing SH2 domains such as Crk, Crk-L, CRKII presumed domain is functionally uncharacterised [1].

1: CAS proteins in normal and pathological cell growth control. Tikhmyanova N, Little JL, Golemis EA; Cell Mol Life Sci. 2010;67:1025-1048. PMID:19937461