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Human neuroglobin functions as a redox-regulated nitrite reductase.

Mauro Tiso1, Jesús Tejero, Swati Basu

  • 1Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.

The Journal of Biological Chemistry
|February 8, 2011
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Neuroglobin, a protein related to hemoglobin, acts as a nitrite reductase, producing nitric oxide (NO). Its activity is controlled by redox-sensitive thiols, suggesting a role in cellular signaling and oxidative stress.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Physiology

Background:

  • Neuroglobin is a conserved hemoprotein with an unknown physiological role.
  • It shares ancestry with hemoglobin and myoglobin.
  • Neuroglobin features a six-coordinate heme with reversible sixth ligand binding.

Purpose of the Study:

  • To investigate the physiological function of neuroglobin.
  • To elucidate the mechanism of nitric oxide (NO) formation by neuroglobin.
  • To determine the role of redox-sensitive thiols and heme coordination in neuroglobin activity.

Main Methods:

  • Site-directed mutagenesis of neuroglobin (distal histidine, Cys-55, Cys-46).
  • Biochemical assays to measure nitrite reductase activity and NO formation.
  • Lentivirus expression systems to study cellular effects.
  • Analysis of NO binding to cytochrome c oxidase.

Main Results:

  • Deoxygenated neuroglobin reacts with nitrite to form NO.
  • Redox-sensitive thiols (Cys-55, Cys-46) regulate NO formation by controlling heme coordination.
  • Mutants with a stable five-coordinate heme (e.g., distal histidine replacement) exhibit significantly faster nitrite reduction.
  • Mutants stabilizing the six-coordinate structure slow the reaction.
  • Neuroglobin's nitrite reductase activity inhibits cellular respiration via NO.
  • Neuroglobin regulates hypoxic NO-signaling pathways through its six-to-five-coordinate status.

Conclusions:

  • Neuroglobin functions as a redox-regulated nitrite reductase, generating NO.
  • Its activity is controlled by the heme pocket's six-to-five-coordinate status.
  • Neuroglobin may act as a physiological sensor for oxidative stress and hypoxia.
  • The heme globin superfamily might serve as ancient NO-signaling proteins in hypoxic conditions.