This is a serine rich domain that is found in the docking protein p130(cas) (Crk-associated substrate). This domain folds into a four helix bundle which is associated with protein-protein interactions [1].

1: The serine-rich domain from Crk-associated substrate (p130cas) is a four-helix bundle. Briknarova K, Nasertorabi F, Havert ML, Eggleston E, Hoyt DW, Li C, Olson AJ, Vuori K, Ely KR; J Biol Chem. 2005;280:21908-21914. PMID:15795225