Oxidative Thiol Modifications as Molecular Redox Sensors in Human Mitochondria

Abstract

Neurodegenerative diseases and ageing are intricately linked with biological cellular levels of reactive oxygen species (ROS). The highest levels of ROS are produced during mitochondrial respiration, and an optimal balance of ROS levels for physiological signaling over cellular damage is regulated by ROS scavengers. In the mitochondrial outer membrane, voltage-dependent anion channels (VDACs) are believed to function in close conjunction with the molecular ROS sensors in the mitochondrial intermembrane space, to balance ROS transport into the cytosolic milieu versus the trigger of mitochondria-mediated apoptosis. However, the role of mitochondrial VDACs, and the molecular elements involved in ROS scavenging, has not yet been identified. In particular, the anti-apoptotic function of human VDAC2 isoform and the unusual abundance of thiolate ions - ¬presented as cysteines in VDAC2 - allowed us to hypothesize that redox homeostasis is effected by VDAC2 cysteines. Using molecular measurements of VDAC2 energetics in native-like environments, single-channel functional studies and insights from oxidative cysteine modifications in vitro and in vivo, we demonstrate that VDAC2 has evolutionary role as a molecular redox regulator. Cysteine enrichment in human VDAC2 is not stochastic, and is essential to counter cellular oxidative challenges and redox stress. For the first time in mitochondrial bioenergetics, our findings demonstrate both a vital role of VDAC2 as a metabolite flux regulator and how this protein is indispensable for oxidative homeostasis and the trigger of mitophagy.