Members of this family are predominantly found in Rabaptin and allow for binding to the GTPase Rab5. This interaction is necessary and sufficient for Rab5-dependent recruitment of Rabaptin5 to early endosomal membranes [1].

1: Structural basis of Rab5-Rabaptin5 interaction in endocytosis. Zhu G, Zhai P, Liu J, Terzyan S, Li G, Zhang XC; Nat Struct Mol Biol. 2004;11:975-983. PMID:15378032