Identification as β-Adducin of a Protein Interacting with Rabphilin-3A in the Presence of Ca2+ and Phosphatidylserine

Rabphilin-3A is a putative target protein for Rab3A small GTP-binding protein implicated in neurotransmitter release. We have previously identified a Rabphilin-3A-interacting protein with a Mr of about 115 kDa in bovine brain. We have attempted here to purify this protein and to determine its primary structure. Amino acid sequence analysis has revealed that this protein is a bovine counterpart of human β-adducin which is known to be a good substrate for protein kinase C. The Rabphilin-3A-interacting protein also binds to protein kinase C in the presence of Ca2+ and phosphatidylserine. These results indicate that Rabphilin-3A binds to β-adducin in the presence of Ca2+ and phosphatidylserine.