Members of this family adopt a helix-loop-helix motif, as per other EF hand domains. However, since they do not contain the canonical pattern of calcium binding residues found in many EF hand domains, they do not bind calcium ions. The main function of this domain is the provision of specificity in beta-dystroglycan recognition, though in dystrophin it serves an additional role: stabilisation of the WW domain (Pfam:PF00397), enhancing dystroglycan binding [1].

1: Structure of a WW domain containing fragment of dystrophin in complex with beta-dystroglycan. Huang X, Poy F, Zhang R, Joachimiak A, Sudol M, Eck MJ; Nat Struct Biol. 2000;7:634-638. PMID:10932245