Molecular cloning and characterization of adult Sparus aurata hemoglobin genes

Among Teleosts, Sparus aurata occupies a prominent place in the gastronomic and economic fields of the Mediterranean basin and other geographic districts. The knowledge of its molecular structures and functional features, such as hemoglobin, may be helpful to understand the adaptive biochemical mechanisms that allow this fish to live under extreme conditions, including fish farming. In Sparus aurata red blood cells two different a and one b hemoglobin genes have been identified. The a1 gene codifies a putative protein of 144 amino acids, the a2 gene produces a protein of 143 amino acids, and the b gene encodes a chain of 148 amino acids. Comparative analysis of various hemoglobins indicates that allosteric regulation can be modified by the substitution of one or a few key residues. The comparison of the percentage sequence differences for a and b chains in fishes indicates that evolutionary relationships between different species may be helpful to understand the mechanisms of their differentiation from other vertebrates. Hemoglobin a and b chains of about 50 teleostean temperate and Antarctic fishes were analyzed to build phylogenetic trees using different algorithms: the neighbor-joining method, the maximum likelihood approach, and the Bayesian inference computation. Sparus aurata a chains are positioned in a paraphyletic cluster, which includes the same subunit of Chrysophrys auratus and Seriola quinqueradiata, whereas the b chain is on an homophyletic branch with that of Chrysophrys auratus. Therefore, the phylogenetic approach suggests that both Sparus aurata hemoglobin a genes are paralogues and may have derived from a duplication event.