Enzyme structure captures four cysteines aligned for disulfide relay. (18th June 2014)

• Record Type: Journal Article
• Authors: Gat, Yair; Vardi‐Kilshtain, Alexandra; Grossman, Iris; Major, Dan Thomas; Fass, Deborah
• Is Part Of: Protein science. Volume 23:Number 8(2014:Aug.)
• Page Start: 1102
• Page End: 1112
• Publication Date: 2014-06-18
• Subjects: Proteins -- Periodicals; 572.6
• DOI: 10.1002/pro.2496
• Languages: English
• ISSNs: 0961-8368

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>Thioredoxin superfamily proteins introduce disulfide bonds into substrates, catalyze the removal of disulfides, and operate in electron relays. These functions rely on one or more dithiol/disulfide exchange reactions. The flavoenzyme quiescin sulfhydryl oxidase (QSOX), a catalyst of disulfide bond formation with an interdomain electron transfer step in its catalytic cycle, provides a unique opportunity for exploring the structural environment of enzymatic dithiol/disulfide exchange. Wild‐type <italic>Rattus norvegicus</italic> QSOX1 (RnQSOX1) was crystallized in a conformation that juxtaposes the two redox‐active di‐cysteine motifs in the enzyme, presenting the entire electron‐transfer pathway and proton‐transfer participants in their native configurations. As such a state cannot generally be enriched and stabilized for analysis, RnQSOX1 gives unprecedented insight into the functional group environments of the four cysteines involved in dithiol/disulfide exchange and provides the framework for analysis of the energetics of electron transfer in the presence of the bound flavin adenine dinucleotide cofactor. Hybrid quantum mechanics/molecular mechanics (QM/MM) free energy simulations based on the X‐ray crystal structure suggest that formation of the interdomain disulfide intermediate is highly favorable and secures the flexible enzyme in a state from which further electron transfer via the flavin can occur.</p> </abstract>