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Structure and function of the globin and globin gene from the Antarctic mollusc Yoldia eightsi.

ABSTRACT: The mechanism of adaptation of haemoglobin from the Antarctic mollusc Yoldia eightsi to its low-temperature environment is a decrease in the oxygen affinity via an increased ligand-dissociation rate. At 2 degrees C this haemoglobin has an oxygen affinity similar to other haemoglobins at 25 degrees C. At 25 degrees C, Yoldia haemoglobin shows a low oxygen affinity, resembling that of human deoxyhaemoglobin. The mechanism involves a lower binding energy to oxygen, suggesting a loss or weakening of the usual hydrogen bond, leading to a higher oxygen-dissociation rate. However, Yoldia haemoglobin has the usual distal and proximal histidines, so the primary structure alone does not provide an obvious explanation for the low affinity. The CO-binding kinetics are biphasic, with the fraction of slow phase increasing at higher protein concentrations, indicating the formation of dimers or a higher level of polymerization. The protein-protein interaction appears to be of hydrophobic nature, since it can be partially reversed by addition of ethylene glycol as co-solvent. While the CO-association rates differ by a factor of 10, the oxygen equilibrium data could be simulated with a single affinity. The Yoldia haemoglobin gene contains three introns, interrupting the coding region at position NA1.2, B12.2 and G7.0. The conservation of the B12.2 and G7.0 introns is in contrast with the unprecedented NA1.2 intron. Phylogenetic analyses reveal a gene tree where the Yoldia haemoglobin gene is separated from other mollusc globin genes, confirming the specific adaptation of the Yoldia haemoglobin.

SUBMITTER: Dewilde S

PROVIDER: S-EPMC1223153 | biostudies-other | 2003 Feb

REPOSITORIES: biostudies-other

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Project description:BACKGROUND:The lancelet amphioxus (Cephalochordata) is a close relative of vertebrates and thus may enhance our understanding of vertebrate gene and genome evolution. In this context, the globins are one of the best studied models for gene family evolution. Previous biochemical studies have demonstrated the presence of an intracellular globin in notochord tissue and myotome of amphioxus, but the corresponding gene has not yet been identified. Genomic resources of Branchiostoma floridae now facilitate the identification, experimental confirmation and molecular evolutionary analysis of its globin gene repertoire. RESULTS:We show that B. floridae harbors at least fifteen paralogous globin genes, all of which reveal evidence of gene expression. The protein sequences of twelve globins display the conserved characteristics of a functional globin fold. In phylogenetic analyses, the amphioxus globin BflGb4 forms a common clade with vertebrate neuroglobins, indicating the presence of this nerve globin in cephalochordates. Orthology is corroborated by conserved syntenic linkage of BflGb4 and flanking genes. The kinetics of ligand binding of recombinantly expressed BflGb4 reveals that this globin is hexacoordinated with a high oxygen association rate, thus strongly resembling vertebrate neuroglobin. In addition, possible amphioxus orthologs of the vertebrate globin X lineage and of the myoglobin/cytoglobin/hemoglobin lineage can be identified, including one gene as a candidate for being expressed in notochord tissue. Genomic analyses identify conserved synteny between amphioxus globin-containing regions and the vertebrate ?-globin locus, possibly arguing against a late transpositional origin of the ?-globin cluster in vertebrates. Some amphioxus globin gene structures exhibit minisatellite-like tandem duplications of intron-exon boundaries ("mirages"), which may serve to explain the creation of novel intron positions within the globin genes. CONCLUSIONS:The identification of putative orthologs of vertebrate globin variants in the B. floridae genome underlines the importance of cephalochordates for elucidating vertebrate genome evolution. The present study facilitates detailed functional studies of the amphioxus globins in order to trace conserved properties and specific adaptations of respiratory proteins at the base of chordate evolution.

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Structure and function of the globin and globin gene from the Antarctic mollusc Yoldia eightsi.

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