Abstract:

<p>Hydrogen sulfide (HS) is a gasotransmitter exhibiting pivotal functions in diverse biological processes, including activation of multiple cardioprotective pathways. Sulfide:quinone oxidoreductase (SQOR) is an integral membrane flavoprotein that catalyzes the first step in the mitochondrial metabolism of HS. As such, it plays a critical role in controlling physiological levels of the gasotransmitter and has attracted keen interest as a potential drug target. We report the crystal structure of human SQOR, unraveling the molecular basis for the enzyme&#39;s ability to catalyze sulfane sulfur transfer reactions with structurally diverse acceptors. We demonstrate that human SQOR contains unique features: an electropositive surface depression implicated as a binding site for sulfane sulfur acceptors and postulated to funnel negatively charged substrates to a hydrophilic HS-oxidizing active site, which is connected to a hydrophobic internal tunnel that binds coenzyme Q. These findings support a proposed model for catalysis and open the door for structure-based drug design.</p>