title: Structural and Mechanistic Insights into Hemoglobin-catalyzed Hydrogen Sulfide Oxidation and the Fate of Polysulfide Products.
abstract: Hydrogen sulfide is a cardioprotective signaling molecule but is toxic at elevated concentrations. Red blood cells can synthesize H2S but, lacking organelles, cannot dispose of H2S via the mitochondrial sulfide oxidation pathway. We have recently shown that at high sulfide concentrations, ferric hemoglobin oxidizes H2S to a mixture of thiosulfate and iron-bound polysulfides in which the latter species predominates. Here, we report the crystal structure of human hemoglobin containing low spin ferric sulfide, the first intermediate in heme-catalyzed sulfide oxidation. The structure provides molecular insights into why sulfide is susceptible to oxidation in human hemoglobin but is stabilized against it in HbI, a specialized sulfide-carrying hemoglobin from a mollusk adapted to life in a sulfide-rich environment. We have also captured a second sulfide bound at a postulated ligand entry/exit site in the α-subunit of hemoglobin, which, to the best of our knowledge, represents the first direct evidence for this site being used to access the heme iron. Hydrodisulfide, a postulated intermediate at the junction between thiosulfate and polysulfide formation, coordinates ferric hemoglobin and, in the presence of air, generated thiosulfate. At low sulfide/heme iron ratios, the product distribution between thiosulfate and iron-bound polysulfides was approximately equal. The iron-bound polysulfides were unstable at physiological glutathione concentrations and were reduced with concomitant formation of glutathione persulfide, glutathione disulfide, and H2S. Hence, although polysulfides are unlikely to be stable in the reducing intracellular milieu, glutathione persulfide could serve as a persulfide donor for protein persulfidation, a posttranslational modification by which H2S is postulated to signal.
authors.affiliation: From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 and.
authors.forename: Victor
authors.initials: V
authors.lastname: Vitvitsky
authors.affiliation: From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 and.
authors.forename: Pramod K
authors.initials: PK
authors.lastname: Yadav
authors.affiliation: From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 and.
authors.forename: Sojin
authors.initials: S
authors.lastname: An
authors.affiliation: the Department of Biochemistry and the Redox Biology Center, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Javier
authors.initials: J
authors.lastname: Seravalli
authors.affiliation: From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 and.
authors.forename: Uhn-Soo
authors.initials: US
authors.lastname: Cho
authors.affiliation: From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109 and rbanerje@umich.edu.
authors.forename: Ruma
authors.initials: R
authors.lastname: Banerjee
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006862:Hydrogen Sulfide / Q000378:metabolism*; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013440:Sulfides / Q000737:chemistry / Q000378:metabolism*; D013885:Thiosulfates / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D013440:Sulfides; D013885:Thiosulfates; C032915:polysulfide; D006862:Hydrogen Sulfide
keywords: crystal structure; heme; hemoglobin; hydrogen sulfide; oxidation-reduction (redox)