title: Human neuroglobin functions as a redox-regulated nitrite reductase.
abstract: Neuroglobin is a highly conserved hemoprotein of uncertain physiological function that evolved from a common ancestor to hemoglobin and myoglobin. It possesses a six-coordinate heme geometry with proximal and distal histidines directly bound to the heme iron, although coordination of the sixth ligand is reversible. We show that deoxygenated human neuroglobin reacts with nitrite to form nitric oxide (NO). This reaction is regulated by redox-sensitive surface thiols, cysteine 55 and 46, which regulate the fraction of the five-coordinated heme, nitrite binding, and NO formation. Replacement of the distal histidine by leucine or glutamine leads to a stable five-coordinated geometry; these neuroglobin mutants reduce nitrite to NO ∼2000 times faster than the wild type, whereas mutation of either Cys-55 or Cys-46 to alanine stabilizes the six-coordinate structure and slows the reaction. Using lentivirus expression systems, we show that the nitrite reductase activity of neuroglobin inhibits cellular respiration via NO binding to cytochrome c oxidase and confirm that the six-to-five-coordinate status of neuroglobin regulates intracellular hypoxic NO-signaling pathways. These studies suggest that neuroglobin may function as a physiological oxidative stress sensor and a post-translationally redox-regulated nitrite reductase that generates NO under six-to-five-coordinate heme pocket control. We hypothesize that the six-coordinate heme globin superfamily may subserve a function as primordial hypoxic and redox-regulated NO-signaling proteins.
authors.affiliation: Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Mauro
authors.initials: M
authors.lastname: Tiso
authors.forename: Jesús
authors.initials: J
authors.lastname: Tejero
authors.forename: Swati
authors.initials: S
authors.lastname: Basu
authors.forename: Ivan
authors.initials: I
authors.lastname: Azarov
authors.forename: Xunde
authors.initials: X
authors.lastname: Wang
authors.forename: Virgil
authors.initials: V
authors.lastname: Simplaceanu
authors.forename: Sheila
authors.initials: S
authors.lastname: Frizzell
authors.forename: Thottala
authors.initials: T
authors.lastname: Jayaraman
authors.forename: Lisa
authors.initials: L
authors.lastname: Geary
authors.forename: Calli
authors.initials: C
authors.lastname: Shapiro
authors.forename: Chien
authors.initials: C
authors.lastname: Ho
authors.forename: Sruti
authors.initials: S
authors.lastname: Shiva
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Kim-Shapiro
authors.forename: Mark T
authors.initials: MT
authors.lastname: Gladwin
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D005914:Globins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000078787:Neuroglobin; D009569:Nitric Oxide / Q000378:metabolism; D009572:Nitrite Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D009573:Nitrites; D009569:Nitric Oxide; D005914:Globins; D009572:Nitrite Reductases