Proapoptotic BH3-only proteins trigger membrane integration of prosurvival Bcl-w and neutralize its activity.
Prosurvival Bcl-2-like proteins, like Bcl-w, are thought to function on organelles such as the mitochondrion and to be targeted to them by their hydrophobic COOH-terminal domain. We unexpectedly found, however, that the membrane association of Bcl-w was enhanced during apoptosis. In healthy cells, Bcl-w was loosely attached to the mitochondrial membrane, but it was converted into an integral membrane protein by cytotoxic signals that induce binding of BH3-only proteins, such as Bim, or by the addition of BH3 peptides to lysates. As the structure of Bcl-w has revealed that its COOH-terminal domain occupies the hydrophobic groove where BH3 ligands bind, displacement of that domain by a BH3 ligand would displace the hydrophobic COOH-terminal residues, allowing their insertion into the membrane. To determine whether BH3 ligation is sufficient to induce the enhanced membrane affinity, or to render Bcl-w proapoptotic, we mimicked their complex by tethering the Bim BH3 domain to the NH2 terminus of Bcl-w. The chimera indeed bound avidly to membranes, in a fashion requiring the COOH-terminal domain, but neither promoted nor inhibited apoptosis. These results suggest that ligation of a proapoptotic BH3-only protein alters the conformation of Bcl-w, enhances membrane association, and neutralizes its survival function.
Wilson-Annan
Julie
J
Walter and Eliza Hall Institute of Medical Research, Victoria 3050, Australia.
O'Reilly
Lorraine A
LA
Crawford
Simon A
SA
Hausmann
George
G
Beaumont
Jennifer G
JG
Parma
Loes P
LP
Chen
Lin
L
Lackmann
Martin
M
Lithgow
Trevor
T
Hinds
Mark G
MG
Day
Catherine L
CL
Adams
Jerry M
JM
Huang
David C S
DC
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism*; D002470:Cell Survival / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism / Q000648:ultrastructure; D024101:Mitochondrial Proteins / Q000378:metabolism; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C491073:BCL2L2 protein, human; C474007:Bax protein (53-86); C491072:Bcl2l2 protein, rat; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D010446:Peptide Fragments; D011506:Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins