title: Globin X is a six-coordinate globin that reduces nitrite to nitric oxide in fish red blood cells.
abstract: The discovery of novel globins in diverse organisms has stimulated intense interest in their evolved function, beyond oxygen binding. Globin X (GbX) is a protein found in fish, amphibians, and reptiles that diverged from a common ancestor of mammalian hemoglobins and myoglobins. Like mammalian neuroglobin, GbX was first designated as a neuronal globin in fish and exhibits six-coordinate heme geometry, suggesting a role in intracellular electron transfer reactions rather than oxygen binding. Here, we report that GbX to our knowledge is the first six-coordinate globin and the first globin protein apart from hemoglobin, found in vertebrate RBCs. GbX is present in fish erythrocytes and exhibits a nitrite reduction rate up to 200-fold faster than human hemoglobin and up to 50-fold higher than neuroglobin or cytoglobin. Deoxygenated GbX reduces nitrite to form nitric oxide (NO) and potently inhibits platelet activation in vitro, to a greater extent than hemoglobin. Fish RBCs also reduce nitrite to NO and inhibit platelet activation to a greater extent than human RBCs, whereas GbX knockdown inhibits this nitrite-dependent NO signaling. The description of a novel, six-coordinate globin in RBCs with dominant electron transfer and nitrite reduction functionality provides new insights into the evolved signaling properties of ancestral heme-globins.
authors.affiliation: Pittsburgh Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA 15213;
authors.forename: Paola
authors.initials: P
authors.lastname: Corti
authors.affiliation: Pittsburgh Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA 15213;
authors.forename: Jianmin
authors.initials: J
authors.lastname: Xue
authors.affiliation: Pittsburgh Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA 15213; Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA 15213;
authors.forename: Jesús
authors.initials: J
authors.lastname: Tejero
authors.affiliation: Department of Physics and the Translational Science Center, Wake Forest University, Winston-Salem, NC 27109;
authors.forename: Nadeem
authors.initials: N
authors.lastname: Wajih
authors.affiliation: Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA 15213;
authors.forename: Ming
authors.initials: M
authors.lastname: Sun
authors.affiliation: Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA 15213;
authors.forename: Donna B
authors.initials: DB
authors.lastname: Stolz
authors.affiliation: Department of Developmental Biology, University of Pittsburgh, Pittsburgh, PA 15213.
authors.forename: Michael
authors.initials: M
authors.lastname: Tsang
authors.affiliation: Department of Physics and the Translational Science Center, Wake Forest University, Winston-Salem, NC 27109;
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Kim-Shapiro
authors.affiliation: Pittsburgh Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA 15213; Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA 15213; gladwinmt@upmc.edu.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Gladwin
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004579:Electron Transport; D004912:Erythrocytes / Q000166:cytology / Q000378:metabolism*; D005399:Fishes / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005914:Globins / Q000235:genetics / Q000378:metabolism*; D006454:Hemoglobins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D010084:Oxidation-Reduction; D034622:RNA Interference; D015027:Zebrafish / Q000097:blood / Q000235:genetics / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D009573:Nitrites; D009569:Nitric Oxide; D005914:Globins
keywords: RBC; blood; nitric oxide; nitrite; platelet