Oligomerization of membrane-bound Bcl-2 is involved in its pore formation induced by tBid.
Both pro-apoptotic Bax and anti-apoptotic Bcl-2 are structurally homologous to the pore-forming domain of bacterial toxins. Bax proteins oligomerize in the mitochondrial outer membranes forming pores that release cytochrome c from the mitochondrial intermembrane space. Bcl-2 proteins also form pores that, however, are much smaller than the Bax pore. It is unknown whether Bcl-2 forms monomeric or oligomeric pores. Here, we characterized the Bcl-2 pore formation in liposomes using biophysical and biochemical techniques. The results show that the Bcl-2 pore enlarges as the concentration of Bcl-2 increases, suggesting that the pore is formed by Bcl-2 oligomers. As expected from oligomerization-mediated pore-formation, the small pores are formed earlier than the large ones. Bcl-2 oligomers form pores faster than the monomer, indicating that the oligomerization constitutes an intermediate step of the pore formation. A Bcl-2 mutant with higher affinity for oligomerization forms pores faster than wild type Bcl-2. Bcl-2 oligomers were detected in the liposomal membranes under conditions that Bcl-2 forms pores, and the extent of oligomerization was positively correlated with the pore-forming activity. Therefore, Bcl-2 oligomerizes in membranes forming pores, but the extent of oligomerization and the size of the resulting pores are much smaller than that of Bax, supporting the model that Bcl-2 is a defective Bax.
Peng
Jun
J
Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73126, USA.
Ding
Jingzhen
J
Tan
Chibing
C
Baggenstoss
Bruce
B
Zhang
Zhi
Z
Lapolla
Suzanne M
SM
Lin
Jialing
J
D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents / Q000494:pharmacology; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D008954:Models, Biological; D008970:Molecular Weight; D009154:Mutation / Q000235:genetics; D018272:Porins / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D051023:BH3 Interacting Domain Death Agonist Protein; D003432:Cross-Linking Reagents; D008081:Liposomes; D018272:Porins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein
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