title: 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 α5 helix was released into the MOM, the remaining interface with α2, α3, and α4 helices was rearranged. Another dimer interface was formed inside the MOM by two intersected or parallel α9 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, α9 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 α9 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 α9 dimerization at the rim.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Sabareesh
authors.initials: S
authors.lastname: Subramaniam
authors.affiliation: Biological Sciences, Sunnybrook Research Institute, Department of Biochemistry, University of Toronto, Toronto, ON, Canada.
authors.forename: Justin
authors.initials: J
authors.lastname: Kale
authors.affiliation: Department of Chemistry, University of Vermont, Burlington, VT, USA.
authors.forename: Chenyi
authors.initials: C
authors.lastname: Liao
authors.affiliation: Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Huang
authors.affiliation: Biological Sciences, Sunnybrook Research Institute, Department of Biochemistry, University of Toronto, Toronto, ON, Canada.
authors.forename: Hetal
authors.initials: H
authors.lastname: Brahmbhatt
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Samson G F
authors.initials: SG
authors.lastname: Condon
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
authors.forename: Suzanne M
authors.initials: SM
authors.lastname: Lapolla
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA Peggy and Charles Stephenson Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
authors.forename: Franklin A
authors.initials: FA
authors.lastname: Hays
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
authors.forename: Jingzhen
authors.initials: J
authors.lastname: Ding
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: He
authors.affiliation: Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
authors.forename: Xuejun C
authors.initials: XC
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, University of Vermont, Burlington, VT, USA.
authors.forename: Jianing
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Senes
authors.affiliation: Biological Sciences, Sunnybrook Research Institute, Department of Biochemistry, University of Toronto, Toronto, ON, Canada.
authors.forename: David W
authors.initials: DW
authors.lastname: Andrews
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA Peggy and Charles Stephenson Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA jialing-lin@ouhsc.edu.
authors.forename: Jialing
authors.initials: J
authors.lastname: Lin
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D019281:Dimerization; D047468:Immunoprecipitation; D051336:Mitochondrial Membranes / Q000378:metabolism*; D011485:Protein Binding; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
keywords: Apoptosis/Bcl‐2 proteins; membrane permeabilization; mitochondrial membranes; oligomerization