title: A hemoglobin with an optical function.
abstract: Hemoglobins are best known as oxygen transport proteins. Here we describe a hemoglobin from the parasitic nematode Mermis nigrescens (Mn-GLB-E) that has an optical, light shadowing function. The protein accumulates to high concentration as intracellular crystals in the ocellus of mature phototactic adult females while also being expressed at low concentration in other tissues. It differs in sequence and expression pattern from Mn-GLB-B, a second Mermis globin. It retains the structure and oxygen-binding and light-absorbing properties typical of nematode hemoglobins. As such, recruitment to a shadowing role in the eye appears to have occurred by changes in expression without modification of biochemistry. Both globins are coded by genes interrupted by two introns at the conserved positions B12.2 and G7.0, which is in agreement with the 3exon/2intron pattern model of globin gene evolution.
authors.affiliation: Department of Biological Sciences, Simon Fraser University, Vancouver, British Columbia V5A 1S6, Canada.
authors.forename: A H
authors.initials: AH
authors.lastname: Burr
authors.forename: P
authors.initials: P
authors.lastname: Hunt
authors.forename: D R
authors.initials: DR
authors.lastname: Wagar
authors.forename: S
authors.initials: S
authors.lastname: Dewilde
authors.forename: M L
authors.initials: ML
authors.lastname: Blaxter
authors.forename: J R
authors.initials: JR
authors.lastname: Vanfleteren
authors.forename: L
authors.initials: L
authors.lastname: Moens
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D018076:DNA, Complementary; D005123:Eye / Q000378:metabolism; D005260:Female; D006454:Hemoglobins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008632:Mermithoidea / Q000502:physiology*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014785:Vision, Ocular / Q000502:physiology*
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D006454:Hemoglobins; C405326:hemoglobin, Mermis nigrescens