Bax monomers form dimer units in the membrane that further self-assemble into multiple oligomeric species.
Bax is a key regulator of apoptosis that mediates the release of cytochrome c to the cytosol via oligomerization in the outer mitochondrial membrane before pore formation. However, the molecular mechanism of Bax assembly and regulation by other Bcl-2 members remains obscure. Here, by analysing the stoichiometry of Bax oligomers at the single-molecule level, we find that Bax binds to the membrane in a monomeric state and then self-assembles in <1 min. Strikingly, active Bax does not exist in a unique oligomeric state, but as several different species based on dimer units. Moreover, we show that cBid activates Bax without affecting its assembly, while Bcl-xL induces the dissociation of Bax oligomers. On the basis of our experimental data and theoretical modelling, we propose a new mechanism for the molecular pathway of Bax assembly to form the apoptotic pore.
Membrane Biophysics, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany.
Yamunadevi
Y
Subburaj
1] Membrane Biophysics, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany [2] Membrane Biophysics, Interfaculty Institute of Biochemistry, University of Tuebingen, Hoppe-Seyler-Strasse 4, 72076 Tuebingen, Germany.
Katia
K
Cosentino
New Materials and Biosystems, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany.
Markus
M
Axmann
1] Membrane Biophysics, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany [2] Membrane Biophysics, Interfaculty Institute of Biochemistry, University of Tuebingen, Hoppe-Seyler-Strasse 4, 72076 Tuebingen, Germany.
Esteban
E
Pedrueza-Villalmanzo
1] Membrane Biophysics, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany [2] Membrane Biophysics, Interfaculty Institute of Biochemistry, University of Tuebingen, Hoppe-Seyler-Strasse 4, 72076 Tuebingen, Germany.
Eduard
E
Hermann
1] Membrane Biophysics, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany [2] Membrane Biophysics, Interfaculty Institute of Biochemistry, University of Tuebingen, Hoppe-Seyler-Strasse 4, 72076 Tuebingen, Germany.
Stephanie
S
Bleicken
New Materials and Biosystems, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany.
Joachim
J
Spatz
1] Membrane Biophysics, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany [2] Membrane Biophysics, Interfaculty Institute of Biochemistry, University of Tuebingen, Hoppe-Seyler-Strasse 4, 72076 Tuebingen, Germany.
Ana J
AJ
García-Sáez
D008051:Lipid Bilayers; D008853:Microscopy / Q000379:methods; D011485:Protein Binding; D013050:Spectrometry, Fluorescence / Q000379:methods; D051028:bcl-2-Associated X Protein / Q000737:chemistry / Q000378:metabolism*
D008051:Lipid Bilayers; D051028:bcl-2-Associated X Protein