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Proapoptotic BH3-only proteins trigger membrane integration of prosurvival Bcl-w and neutralize its activity.

Wilson-Annan J, O'Reilly LA, Crawford SA, Hausmann G, Beaumont JG, Parma LP, Chen L, Lackmann M, Lithgow T, Hinds MG, Day CL, Adams JM, Huang DC - J. Cell Biol. (2003)

Bottom Line: We unexpectedly found, however, that the membrane association of Bcl-w was enhanced during apoptosis.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.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.

View Article: PubMed Central - PubMed

Affiliation: Walter and Eliza Hall Institute of Medical Research, Victoria 3050, Australia.

ABSTRACT
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.

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Model for the inactivation of prosurvival Bcl-2–like proteins by the BH3-only proteins. It is proposed that prosurvival family members, like Bcl-w, normally bind and sequester a membrane-bound effector protein (X) required for Bax/Bak activation. The engagement of a BH3-only protein (Bim here) frees X and allows it, directly or indirectly, to activate Bax and Bak, thereby initiating apoptosis.
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fig7: Model for the inactivation of prosurvival Bcl-2–like proteins by the BH3-only proteins. It is proposed that prosurvival family members, like Bcl-w, normally bind and sequester a membrane-bound effector protein (X) required for Bax/Bak activation. The engagement of a BH3-only protein (Bim here) frees X and allows it, directly or indirectly, to activate Bax and Bak, thereby initiating apoptosis.

Mentions: We favor a model in which Bcl-2–like proteins normally sequester a postulated downstream effector, needed for activation of Bax/Bak and/or caspases (Fig. 7) (Cory and Adams, 2002). In this model, the chimera might be inactive because it can no longer bind the effector. If so, such an effector (X) might be bound only by the conformer of Bcl-w with the COOH-terminal residues in the groove but displaced upon BH3 binding of Bcl-w. Interestingly, although the COOH-terminal residues of Bcl-w are dispensable for binding to BH3-only proteins, they are essential for the biological activity of Bcl-w (Hinds et al., 2003). That observation, together with the data presented here, prompts us to predict that the COOH-terminal residues of prosurvival family members are required for binding to a membrane-bound effector protein akin to that proposed in Fig. 7.


Proapoptotic BH3-only proteins trigger membrane integration of prosurvival Bcl-w and neutralize its activity.

Wilson-Annan J, O'Reilly LA, Crawford SA, Hausmann G, Beaumont JG, Parma LP, Chen L, Lackmann M, Lithgow T, Hinds MG, Day CL, Adams JM, Huang DC - J. Cell Biol. (2003)

Model for the inactivation of prosurvival Bcl-2–like proteins by the BH3-only proteins. It is proposed that prosurvival family members, like Bcl-w, normally bind and sequester a membrane-bound effector protein (X) required for Bax/Bak activation. The engagement of a BH3-only protein (Bim here) frees X and allows it, directly or indirectly, to activate Bax and Bak, thereby initiating apoptosis.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172834&req=5

fig7: Model for the inactivation of prosurvival Bcl-2–like proteins by the BH3-only proteins. It is proposed that prosurvival family members, like Bcl-w, normally bind and sequester a membrane-bound effector protein (X) required for Bax/Bak activation. The engagement of a BH3-only protein (Bim here) frees X and allows it, directly or indirectly, to activate Bax and Bak, thereby initiating apoptosis.
Mentions: We favor a model in which Bcl-2–like proteins normally sequester a postulated downstream effector, needed for activation of Bax/Bak and/or caspases (Fig. 7) (Cory and Adams, 2002). In this model, the chimera might be inactive because it can no longer bind the effector. If so, such an effector (X) might be bound only by the conformer of Bcl-w with the COOH-terminal residues in the groove but displaced upon BH3 binding of Bcl-w. Interestingly, although the COOH-terminal residues of Bcl-w are dispensable for binding to BH3-only proteins, they are essential for the biological activity of Bcl-w (Hinds et al., 2003). That observation, together with the data presented here, prompts us to predict that the COOH-terminal residues of prosurvival family members are required for binding to a membrane-bound effector protein akin to that proposed in Fig. 7.

Bottom Line: We unexpectedly found, however, that the membrane association of Bcl-w was enhanced during apoptosis.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.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.

View Article: PubMed Central - PubMed

Affiliation: Walter and Eliza Hall Institute of Medical Research, Victoria 3050, Australia.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus