ANALYSIS OF INTERACTION SITES IN HOMOMERIC AND HETEROMERIC COMPLEXES CONTAINING BCL-2 FAMILY MEMBERS AND THE CELLULAR PRION PROTEIN

The cellular prion protein (PrP) binds to the C-terminus of Bcl-2 but not Bax. Therefore, we examined whether the C-terminus of Bcl-2 was im portant for other homomeric and heteromeric protein-protein interactio ns. Using the yeast two hybrid system and co-immunoprecipitation, thre e sites of homomeric interactions were identified within Bcl-2. The ca rboxy terminal 37 amino acids selectively homodimerized. Two additiona l regions of Bcl-2 (residues 1-129 and 126-200) interacted with each o ther, but not themselves permitting both intra- and intermolecular ass ociation. In addition, we analyzed heteromeric interactions of Bcl-2 w ith PrP and two Bcl-2 related proteins, Bax and A1. The domain require ments for binding of those three proteins to Bcl-2 were different from one another. Bar binding required almost the entire Bcl-2 molecule, w hile A1 bound to the amino terminal region (residues 1-82). PrP associ ated with the carboxy terminus of Bcl-2 (amino acids 200-236). These d ata suggest configurational models for Bcl-2 containing complexes. Fir st, Bcl-2 may exist as both heterodimers and heteromultimers. Second, molecules such as Bax and A1 may serve to cap chains of Bcl-2 homodime rs by interacting with dimerization domains in the extramembrane regio n. PrP may disrupt chains of Bcl-2 molecules at the homomeric associat ion site in the transmembrane region.