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Enzymology of H 2 S Oxidation in Nanodiscs
Author(s) -
Landry Aaron Paul,
Banerjee Ruma
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.920.9
Subject(s) - chemistry , cysteine , electron transport chain , cofactor , biochemistry , biophysics , flavin group , reductase , enzyme , combinatorial chemistry , biology
The mitochondrial sulfide oxidation pathway is critical for regulating levels of hydrogen sulfide (H 2 S), which plays critical signaling roles in mammals leading to cardioprotection, neuroprotection, and anti‐inflammatory responses in the gastrointestinal system. The first and committed step of this pathway is catalyzed by sulfide‐quinone oxidoreductase (SQR), a membrane‐bound, flavin‐dependent disulfide reductase. SQR converts H 2 S to an enzyme‐bound cysteine persulfide and subsequently transfers the sulfane sulfur to a small molecule acceptor ( Figure 1). Concomitant with the latter step, the cysteine disulfide reforms in the active site while the electrons from sulfide oxidation are relayed to the FAD cofactor, to coenzyme Q 10 , and thereon to complex III in the electron transport chain, thus coupling sulfide oxidation to mitochondrial energy metabolism. While the pivotal role of SQR in H 2 S clearance makes it an attractive therapeutic target in diseases attributed to dysregulated H 2 S levels, key features of the SQR reaction mechanism are unclear and studies have been hindered by the limited solubility of this membrane‐bound enzyme. In the present study, we have elucidated the enzymology of human SQR in a membrane environment by incorporating it into nanodiscs ( Figure 2). Kinetic analyses of the nanodisc‐bound SQR reveal enhanced activity with several small‐molecule acceptors compared to the detergent‐solubilized form of the enzyme, while stopped‐flow studies further elucidated the pre‐steady state catalytic mechanism and the kinetics of FAD‐mediated quinone reduction. These results provide new insight into the role of SQR in H 2 S metabolism and establish a foundation for therapeutic targeting of this enzyme. Support or Funding Information R01‐GGM112455 (NIH) 7/1/2014 ‐ 6/30/2018, Enzymology of Sulfide Oxidation 1Postulated SQR reaction mechanism, with transfer of sulfane sulfur to a generic small molecule (RSH).2Scheme for incorporation of detergent‐solubilized SQR into nanodiscs.