Krammer Eva-Maria, Vu Giang Thi, Homblé Fabrice, Prévost Martine
Structure et Fonction des Membranes Biologiques, Centre de Biologie Structurale et de Bioinformatique, Université Libre de Bruxelles (ULB), Brussels, Belgium.
PLoS One. 2015 Apr 10;10(4):e0121746. doi: 10.1371/journal.pone.0121746. eCollection 2015.
In the exchange of metabolites and ions between the mitochondrion and the cytosol, the voltage-dependent anion channel (VDAC) is a key element, as it forms the major transport pathway for these compounds through the mitochondrial outer membrane. Numerous experimental studies have promoted the idea that VDAC acts as a regulator of essential mitochondrial functions. In this study, using a combination of molecular dynamics simulations, free-energy calculations, and electrophysiological measurements, we investigated the transport of ions through VDAC, with a focus on phosphate ions and metabolites. We showed that selectivity of VDAC towards small anions including monovalent phosphates arises from short-lived interactions with positively charged residues scattered throughout the pore. In dramatic contrast, permeation of divalent phosphate ions and phosphate metabolites (AMP and ATP) involves binding sites along a specific translocation pathway. This permeation mechanism offers an explanation for the decrease in VDAC conductance measured in the presence of ATP or AMP at physiological salt concentration. The binding sites occur at similar locations for the divalent phosphate ions, AMP and ATP, and contain identical basic residues. ATP features a marked affinity for a central region of the pore lined by two lysines and one arginine of the N-terminal helix. This cluster of residues together with a few other basic amino acids forms a "charged brush" which facilitates the passage of the anionic metabolites through the pore. All of this reveals that VDAC controls the transport of the inorganic phosphates and phosphate metabolites studied here through two different mechanisms.
在线粒体与细胞质之间代谢物和离子的交换过程中，电压依赖性阴离子通道（VDAC）是关键因素，因为它构成了这些化合物通过线粒体外膜的主要运输途径。大量实验研究支持了VDAC作为线粒体基本功能调节因子的观点。在本研究中，我们结合分子动力学模拟、自由能计算和电生理测量，研究了离子通过VDAC的运输，重点关注磷酸根离子和代谢物。我们发现，VDAC对包括单价磷酸盐在内的小阴离子的选择性源于与遍布孔道的带正电残基的短暂相互作用。与之形成鲜明对比的是，二价磷酸根离子和磷酸代谢物（AMP和ATP）的通透涉及沿特定转运途径的结合位点。这种通透机制解释了在生理盐浓度下，存在ATP或AMP时测得的VDAC电导降低的现象。二价磷酸根离子、AMP和ATP的结合位点位于相似位置，且包含相同的碱性残基。ATP对由N端螺旋的两个赖氨酸和一个精氨酸构成的孔道中心区域具有显著亲和力。这一簇残基与其他一些碱性氨基酸共同形成了一个“带电刷”，有助于阴离子代谢物通过孔道。所有这些都表明，VDAC通过两种不同机制控制此处研究的无机磷酸盐和磷酸代谢物的运输。
