Acidic pH promotes oligomerization and membrane insertion of the BclXL apoptotic repressor

► pH tightly modulates oligomerization of BclXL. ► Acidic pH promotes the assembly of BclXL into a megadalton oligomer. ► BclXL displays structural features characteristic of a molten globule under acidic pH. ► Membrane insertion of BclXL is favored under acidic pH. ► Ligand binding to BclXL is compromised under acidic and alkaline pH.