Allosteric regulation of BH3-in-groove interactions by tail anchors of BCL-xL complexes limits BH3 mimetic antagonism.

Abstract

In briefThe C terminal tail anchors of BCL-2 family proteins exert allosteric influence over the interface crucial for BH3 binding and cell survival. This is regulated by additional features taking place at the mitochondria membrane such as recruitment of the death executioner BAX, which, in response to BH3 binding antagonism, contributes to protein complex disruption. SummaryBCL-xL exerts an essential cell survival function which relies on its hydrophobic groove binding to BH3 domain of BH3-only initiators and downstream BAX/BAK executioners. Combining resonance energy transfer assays and molecular dynamics simulations, we unravel that the C-terminal tail mediated subcellular membrane anchoring of BCL-xL selectively advantages binding to membrane-anchored PUMA initiator over BH3 mimetic ligands of the groove. This is due to the combined allosteric effect on BH3-in-groove binding of BCL-xL and PUMA tail anchors. Moreover, doubly anchored PUMA / BCL-xL complexes recruit endogenous BAX, which favors their antagonism by BH3 mimetics. BAXs C-terminal tail anchor alone is sufficient to enhance BH3 mimetics induced death in cells expressing PUMA / BCL-xL. Thus, the survival function of BCL-xL is regulated by a complex interplay between its tail anchor and those of its interacting partners. This enables both resistance to pharmacological inhibitors and modulation by BAX, which functions as a crucial feedback disruptor of the BCL-xL network. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/616265v1_ufig1.gif" ALT="Figure 1000"> View larger version (12K): org.highwire.dtl.DTLVardef@885687org.highwire.dtl.DTLVardef@e8eeaeorg.highwire.dtl.DTLVardef@8e09fborg.highwire.dtl.DTLVardef@1314d68_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsBH3 mimetic antagonism, and subsequent cell death, are limited when full length BCL-xL binds to some membrane-anchored BH3-only proteins such as PUMA. The BH3-in-groove interface is allosterically modulated by tail anchors of PUMA and BCL-xL. Binding to PUMA enriches BCL-xL interactome and recruits BAX. BAX counteracts the effects of tail anchors in BCL-xL complexes.