Biophysical characterization of recombinant human Bcl-2 and its interactions with an inhibitory ligand, antimycin A

Apoptosis is an essential physiological process, regulated by the family of Bcl-2-related proteins. However, the molecular mechanism by which Bcl-2 regulates apoptosis still remains elusive. Here we report the functional studies of recombinant human Bcl-2 with the deletion of 22 residues at the C-terminal membrane-anchoring region (rhBcl-2 Delta 22). Characterization of rhBcl-2 Delta 22 showed that the recombinant protein is homogeneous and monodisperse in nondenaturing solutions, stable at room temperature in the presence of a metal chelator, and an or-helical protein with unfolding of secondary structure at a T, of 62.8 degreesC. Optimal membrane pore formation by rhBcl-2 Delta 22 required negatively charged phospholipids. The existence of a hydrophobic groove in rhBcl-2 Delta 22 was demonstrated by the fluorescence enhancement of the hydrophobic ANS probe with which a pro-apoptotic Bak BH3 peptide competed. The respiratory inhibitor antimycin A also bound to the hydrophobic groove of rhBcl-2 Delta 22 with a K-d of 0.82 muM The optimal binding conformation of antimycin A was predicted from molecular docking of antimycin A with the hBcl-2 model created by homology modeling. Antimycin A selectively induces apoptosis in cells overexpressing Bcl-2, suggesting that hydrophobic groove-binding compounds may act as selective apoptotic triggers in tumor cells.