BAX-Induced Apoptosis Can Be Initiated through a Conformational Selection Mechanism

Tsai, Chien Hsiung; Liu, Sophia; Hung, Chien‐Lun; Jhong, Siao-Ru; Sung, Tai-Ching; Chiang, Yun‐Wei

doi:10.1016/j.str.2014.10.016

Cited by 29 publications

(41 citation statements)

References 38 publications

(45 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As well, Q-band DEER measurements provide an order of magnitude greater gain in sensitivity versus those performed at X-band (Polyhach et al, 2012). Therefore, if another conformational analog of Bax were present, and at the relative populations (∼20% or greater) reported previously (Tsai et al, 2015), then it should be observed in our DEER distance distributions.…”

Section: Resultssupporting

confidence: 60%

“…(Renault and Chipuk, 2014; Renault and Manon, 2011; Schellenberg et al, 2013; Suzuki et al, 2000; Youle and Strasser, 2008). Recently, however, it was reported, using the mouse homolog of Bax, that monomeric Bax is in equilibrium between two conformationally distinct states, with the previously unobserved state serving as a transitionary state to Bax's membrane-bound form (Tsai et al, 2015; Kao et al, 2017). Using electron paramagnetic resonance double electron-electron resonance at varying temperatures and pressures, Chiang and coworkers “captured” and provided a structural model of this “new” form of monomeric Bax.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Conformational Heterogeneity in the Activation Mechanism of Bax

et al. 2017

View full text Add to dashboard Cite

Bax is known for its pro-apoptotic role within the mitochondrial pathway of apoptosis. However, the mechanism for transitioning Bax from cytosolic to membrane-bound oligomer remain elusive. Previous nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) studies defined monomeric Bax as conformationally homogenous. Yet, it has, recently, been proposed that monomeric Bax exists in equilibrium with a minor state that is distinctly different from its NMR structure. Here, we revisited the structural analysis of Bax using methods uniquely suited for unveiling “invisible” states of proteins, namely, NMR paramagnetic relaxation enhancements (PREs) and EPR double electron-electron resonance (DEER). Additionally, we examined the effect of glycerol, the co-solvent of choice in DEER studies, on the structure of Bax using NMR chemical shift perturbations (CSPs) and residual dipolar couplings (RDCs). Based on our combined NMR and EPR results, Bax is a conformationally homogenous protein prior to its activation.

show abstract

Section: Resultssupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Conformational Heterogeneity in the Activation Mechanism of Bax

et al. 2017

View full text Add to dashboard Cite

show abstract

“…HXMS and mutagenesis showed that 3G11 binds to an extended surface on BAX that includes the N-terminal activation site (helices ␣1/␣6), which BIM, tBID, and p53 upregulated modulator of apoptosis (PUMA) pro-apoptotic BH3 helices bind to trigger BAX activation (10,11,37,39,42). Therefore, our data are consistent with 3G11 competitively inhibiting tBID-mediated BAX activation by blocking access to the N-terminal trigger site and preventing N-terminal conformational changes associated with BAX activation (11,37).…”

Section: Discussionmentioning

confidence: 99%

Synthetic Antibodies Inhibit Bcl-2-associated X Protein (BAX) through Blockade of the N-terminal Activation Site

Uchime

Dai

Biris

et al. 2016

Journal of Biological Chemistry

View full text Add to dashboard Cite

The BCL-2 protein family plays a critical role in regulating cellular commitment to mitochondrial apoptosis. Pro-apoptotic Bcl-2-associated X protein (BAX) is an executioner protein of the BCL-2 family that represents the gateway to mitochondrial apoptosis. Following cellular stresses that induce apoptosis, cytosolic BAX is activated and translocates to the mitochondria, where it inserts into the mitochondrial outer membrane to form a toxic pore. How the BAX activation pathway proceeds and how this may be inhibited is not yet completely understood. Here we describe synthetic antibody fragments (Fabs) as structural and biochemical probes to investigate the potential mechanisms of BAX regulation. These synthetic Fabs bind with high affinity to BAX and inhibit its activation by the BH3-only protein tBID (truncated Bcl2 interacting protein) in assays using liposomal membranes. Inhibition of BAX by a representative Fab, 3G11, prevented mitochondrial translocation of BAX and BAX-mediated cytochrome c release. Using NMR and hydrogen-deuterium exchange mass spectrometry, we showed that 3G11 forms a stoichiometric and stable complex without inducing a significant conformational change on monomeric and inactive BAX. We identified that the Fab-binding site on BAX involves residues of helices ␣1/␣6 and the ␣1-␣2 loop. Therefore, the inhibitory binding surface of 3G11 overlaps with the N-terminal activation site of BAX, suggesting a novel mechanism of BAX inhibition through direct binding to the BAX N-terminal activation site. The synthetic Fabs reported here reveal, as probes, novel mechanistic insights into BAX inhibition and provide a blueprint for developing inhibitors of BAX activation.Apoptosis plays a critical role in maintaining normal tissue homoeostasis in multicellular organisms, and its deregulation results in an imbalance of homeostasis contributing to several diseases (1, 2) The BCL-2 protein family plays a central role in regulating the mitochondrial pathway of apoptosis (3, 4). Mitochondrial outer membrane permeabilization (MOMP) 5 is considered the key event that is regulated by the complex network of protein-protein interactions between pro-apoptotic and anti-apoptotic members of the BCL-2 family. Activation of the pro-apoptotic members Bcl-2-associated X protein (BAX) and/or Bcl2-antagonist/killer 1 (BAK) is required for induction of MOMP, whereas the anti-apoptotic or survival proteins, such as BCL-2, BCL-X L , and MCL-1, inhibit the pro-apoptotic proteins and prevent MOMP. Activation of BAX and BAK or inhibition of anti-apoptotic BCL-2 proteins is regulated by direct interaction with the BH3-only proteins.The activation pathway of BAX represents the gateway to apoptosis, and understanding the function of BAX and its regulation mechanisms is an area of intensive investigation. BAX is found predominantly in the cytosolic compartment in an inactive conformation (5, 6). Upon cellular stress, BAX is triggered and undergoes a series of conformational changes that enable its translocation to the mitochondrial...

show abstract

“…This lack of rigor has caused debate and confusion. In many studies, the detection of active conformations for the unbound protein has been taken as the indicator for conformational selection as the dominant pathway (5, 11, 18, 40, 42, 43, 67, 73, 80, 82, 87, 92). As has been noted (22, 30), every conformation, whether inactive or active, is sampled with an equilibrium probability given by the Boltzmann distribution; whether active conformations can be detected depends on the sensitivity of the probe used and therefore must not decide the binding mechanism.…”

Section: Theoretical Foundationmentioning

confidence: 99%

Rate Constants and Mechanisms of Protein–Ligand Binding

Pang

Zhou

2017

Annu. Rev. Biophys.

View full text Add to dashboard Cite

Whereas protein–ligand binding affinities have long-established prominence, binding rate constants and binding mechanisms have gained increasing attention in recent years. Both new computational methods and new experimental techniques have been developed to characterize the latter properties. It is now realized that binding mechanisms, like binding rate constants, can and should be quantitatively determined. In this review, we summarize studies and synthesize ideas on several topics in the hope of providing a coherent picture of and physical insight into binding kinetics. The topics include microscopic formulation of the kinetic problem and its reduction to simple rate equations; computation of binding rate constants; quantitative determination of binding mechanisms; and elucidation of physical factors that control binding rate constants and mechanisms.

show abstract

BAX-Induced Apoptosis Can Be Initiated through a Conformational Selection Mechanism

Cited by 29 publications

References 38 publications

Conformational Heterogeneity in the Activation Mechanism of Bax

Conformational Heterogeneity in the Activation Mechanism of Bax

Synthetic Antibodies Inhibit Bcl-2-associated X Protein (BAX) through Blockade of the N-terminal Activation Site

Rate Constants and Mechanisms of Protein–Ligand Binding

Contact Info

Product

Resources

About