BH3-in-groove dimerization initiates and helix 9 dimerization expands Bax pore assembly in membranes.

ABSTRACT: Pro-apoptotic Bax induces mitochondrial outer membrane permeabilization (MOMP) by forming oligomers through a largely undefined process. Using site-specific disulfide crosslinking, compartment-specific chemical labeling, and mutational analysis, we found that activated integral membrane Bax proteins form a BH3-in-groove dimer interface on the MOM surface similar to that observed in crystals. However, after the ?5 helix was released into the MOM, the remaining interface with ?2, ?3, and ?4 helices was rearranged. Another dimer interface was formed inside the MOM by two intersected or parallel ?9 helices. Combinations of these interfaces generated oligomers in the MOM. Oligomerization was initiated by BH3-in-groove dimerization, without which neither the other dimerizations nor MOMP occurred. In contrast, ?9 dimerization occurred downstream and was required for release of large but not small proteins from mitochondria. Moreover, the release of large proteins was facilitated by ?9 insertion into the MOM and localization to the pore rim. Therefore, the BH3-in-groove dimerization on the MOM nucleates the assembly of an oligomeric Bax pore that is enlarged by ?9 dimerization at the rim.

SUBMITTER: Zhang Z 

PROVIDER: S-EPMC4718459 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature