title: The nerve hemoglobin of the bivalve mollusc Spisula solidissima: molecular cloning, ligand binding studies, and phylogenetic analysis.
abstract: Members of the hemoglobin (Hb) superfamily are present in nerve tissue of several vertebrate and invertebrate species. In vertebrates they display hexacoordinate heme iron atoms and are typically expressed at low levels (microM). Their function is still a matter of debate. In invertebrates they have a hexa- or pentacoordinate heme iron, are mostly expressed at high levels (mM), and have been suggested to have a myoglobin-like function. The native Hb of the surf clam, Spisula solidissima, composed of 162 amino acids, does not show specific deviations from the globin templates. UV-visible and resonance Raman spectroscopy demonstrate a hexacoordinate heme iron. Based on the sequence analogy, the histidine E7 is proposed as a sixth ligand. Kinetic and equilibrium measurements show a moderate oxygen affinity (P(50) approximately 0.6 torr) and no cooperativity. The histidine binding affinity is 100-fold lower than in neuroglobin. Phylogenetic analysis demonstrates a clustering of the S. solidissima nerve Hb with mollusc Hbs and myoglobins, but not with the vertebrate neuroglobins. We conclude that invertebrate nerve Hbs expressed at high levels are, despite the hexacoordinate nature of their heme iron, not essentially different from other intracellular Hbs. They most likely fulfill a myoglobin-like function and enhance oxygen supply to the neurons.
authors.affiliation: Department of Biomedical Sciences, University of Antwerp, Campus Drie eiken, Universiteitsplein 1, B-2610 Antwerp, Belgium.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Dewilde
authors.forename: Bettina
authors.initials: B
authors.lastname: Ebner
authors.forename: Evi
authors.initials: E
authors.lastname: Vinck
authors.forename: Kambiz
authors.initials: K
authors.lastname: Gilany
authors.forename: Thomas
authors.initials: T
authors.lastname: Hankeln
authors.forename: Thorsten
authors.initials: T
authors.lastname: Burmester
authors.forename: Jill
authors.initials: J
authors.lastname: Kreiling
authors.forename: Carol
authors.initials: C
authors.lastname: Reinisch
authors.forename: Jacques R
authors.initials: JR
authors.lastname: Vanfleteren
authors.forename: Laurent
authors.initials: L
authors.lastname: Kiger
authors.forename: Michael C
authors.initials: MC
authors.lastname: Marden
authors.forename: Christian
authors.initials: C
authors.lastname: Hundahl
authors.forename: Angela
authors.initials: A
authors.lastname: Fago
authors.forename: Sabine
authors.initials: S
authors.lastname: Van Doorslaer
authors.forename: Luc
authors.initials: L
authors.lastname: Moens
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D006454:Hemoglobins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D016415:Sequence Alignment; D049890:Spisula / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D009419:Nerve Tissue Proteins; D010100:Oxygen