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Proc Natl Acad Sci U S A. 2018 Jan 9;115(2):E172-E179. doi: 10.1073/pnas.1715464115. Epub 2017 Dec 26.

Protonation state of glutamate 73 regulates the formation of a specific dimeric association of mVDAC1.

Author information

1
Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095.
2
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095.
3
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095.
4
Department of Chemistry, Texas A&M University, College Station, TX 77843.
5
Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158.
6
Jules Stein Eye Institute, University of California, Los Angeles, CA 90095; hubbellw@jsei.ucla.edu jabramson@mednet.ucla.edu.
7
Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095; hubbellw@jsei.ucla.edu jabramson@mednet.ucla.edu.
8
Institute for Stem Cell Biology and Regenerative Medicine, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India.

Abstract

The voltage-dependent anion channel (VDAC) is the most abundant protein in the outer mitochondrial membrane and constitutes the primary pathway for the exchange of ions and metabolites between the cytosol and the mitochondria. There is accumulating evidence supporting VDAC's role in mitochondrial metabolic regulation and apoptosis, where VDAC oligomerization has been implicated with these processes. Herein, we report a specific pH-dependent dimerization of murine VDAC1 (mVDAC1) identified by double electron-electron resonance and native mass spectrometry. Intermolecular distances on four singly spin-labeled mVDAC1 mutants were used to generate a model of the low-pH dimer, establishing the presence of residue E73 at the interface. This dimer arrangement is different from any oligomeric state previously described, and it forms as a steep function of pH with an apparent pKa of 7.4. Moreover, the monomer-dimer equilibrium affinity constant was determined using native MS, revealing a nearly eightfold enhancement in dimerization affinity at low pH. Mutation of E73 to either alanine or glutamine severely reduces oligomerization, demonstrating the role of protonated E73 in enhancing dimer formation. Based on these results, and the known importance of E73 in VDAC physiology, VDAC dimerization likely plays a significant role in mitochondrial metabolic regulation and apoptosis in response to cytosolic acidification during cellular stress.

KEYWORDS:

DEER; VDAC; cellular stress; dimerization; native mass spectrometry

PMID:
29279396
PMCID:
PMC5777057
DOI:
10.1073/pnas.1715464115
[Indexed for MEDLINE]
Free PMC Article

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