Abstract
The voltage-dependent anion channel (VDAC) forms the primary diffusion pore of the outer mitochondrial membrane. In its apo form, VDAC adopts an open conformation with high conductance. States of lower conductance can be induced by ligand binding or the application of voltage. Here, we clarify at the atomic level how β-NADH binding leads to a low-conductance state and characterize the role of the VDAC N-terminal helix in voltage gating. A high-resolution NMR structure of human VDAC-1 with bound NADH, combined with molecular dynamics simulation show that β-NADH binding reduces the pore conductance sterically without triggering a structural change. Electrophysiology recordings of crosslinked protein variants and NMR relaxation experiments probing different time scales show that increased helix dynamics is present in the open state and that motions of the N-terminal helices are involved in the VDAC voltage gating mechanism.
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•β-NADH binding to hVDAC-1 does not change conformation of N-terminal helices•β-NADH binding leads to low VDAC conductance by sterically blocking anion flux•Elevated dynamics of the N-terminal helices are present in the ground state•Movements of helix α2 are important for VDAC gating
Böhm et al. demonstrate that the ligand- and the voltage-induced low-conductance states of the mitochondrial membrane protein hVDAC-1 are fundamentally different. β-NADH binding to hVDAC-1 blocks anion flux sterically without conformational changes, while voltage-induced gating is based on dynamics of the N-terminal helices.