Center for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada.
Advanced Computing for Life Sciences and Engineering, Computing and Computational Sciences, National Center for Computational Sciences, Oak Ridge National Lab, Oak Ridge, Tennessee 37830, United States.
J Am Chem Soc. 2022 Aug 17;144(32):14564-14577. doi: 10.1021/jacs.2c03316. Epub 2022 Aug 4.
The voltage-dependent anion channel (VDAC) is a β-barrel channel of the mitochondrial outer membrane (MOM) that passively transports ions, metabolites, polypeptides, and single-stranded DNA. VDAC responds to a transmembrane potential by "gating," i.e. transitioning to one of a variety of low-conducting states of unknown structure. The gated state results in nearly complete suppression of multivalent mitochondrial metabolite (such as ATP and ADP) transport, while enhancing calcium transport. Voltage gating is a universal property of β-barrel channels, but VDAC gating is anomalously sensitive to transmembrane potential. Here, we show that a single residue in the pore interior, K12, is responsible for most of VDAC's voltage sensitivity. Using the analysis of over 40 μs of atomistic molecular dynamics (MD) simulations, we explore correlations between motions of charged residues inside the VDAC pore and geometric deformations of the β-barrel. Residue K12 is bistable; its motions between two widely separated positions along the pore axis enhance the fluctuations of the β-barrel and augment the likelihood of gating. Single channel electrophysiology of various K12 mutants reveals a dramatic reduction of the voltage-induced gating transitions. The crystal structure of the K12E mutant at a resolution of 2.6 Å indicates a similar architecture of the K12E mutant to the wild type; however, 60 μs of atomistic MD simulations using the K12E mutant show restricted motion of residue 12, due to enhanced connectivity with neighboring residues, and diminished amplitude of barrel motions. We conclude that β-barrel fluctuations, governed particularly by residue K12, drive VDAC gating transitions.
电压依赖性阴离子通道 (VDAC) 是线粒体外膜 (MOM) 的 β-桶状通道，可被动转运离子、代谢物、多肽和单链 DNA。VDAC 通过“门控”（即转换为各种未知结构的低导通状态）对跨膜电位做出反应。门控状态导致多价线粒体代谢物（如 ATP 和 ADP）的转运几乎完全受到抑制，同时增强钙转运。电压门控是β-桶状通道的普遍特性，但 VDAC 门控对跨膜电位异常敏感。在这里，我们表明，孔内的单个残基 K12 负责 VDAC 大部分的电压敏感性。使用超过 40 μs 的原子分子动力学 (MD) 模拟分析，我们探索了带电荷残基在 VDAC 孔内的运动与β-桶几何变形之间的相关性。残基 K12 是双稳态的；它在孔轴上两个相距很远的位置之间的运动增强了β-桶的波动，并增加了门控的可能性。各种 K12 突变体的单通道电生理学揭示了电压诱导的门控转变的显著减少。分辨率为 2.6 Å 的 K12E 突变体的晶体结构表明 K12E 突变体与野生型的结构相似；然而，使用 K12E 突变体的 60 μs 原子 MD 模拟显示，由于与相邻残基的连接增强，残基 12 的运动受限，并且桶运动的幅度减小。我们得出的结论是，β-桶的波动，特别是由残基 K12 控制，驱动 VDAC 门控转变。
