Barbary sheep (Ammotragus lervia): The structure of the adult β-globin gene and the functional properties of its hemoglobin

The adult β-globin gene of Ammotragus lervia (Barbary sheep or aoudad) has been sequenced completely, including 185 base pairs of 5′ flanking region and 168 base pairs 3′ to the stop codon, and compared with that of other caprines such as goat (Capra hircus), wild Corsico-Sardinian (Ovis aries musimon) and Cypriot (O. a. ophion) mouflons, and domestic sheep (Ovis aries). The gene was identified as being located on a triplicated four-gene set cluster containing the HBBA locus (A-haplotype) as is the case of goat, sheep of the Hb A type and Corsico-Sardinian mouflon. Phylogenetic analyses support the evidence that caprines share a common ancestor that probably carried the A-haplotype and that a more recent deletion of a gene set gave rise to the duplicated cluster containing the HBBB locus (B-haplotype) found in sheep of the Hb B type and Cypriot mouflon, which evolved independently. Data also suggests that the Ammotragus β-globin gene is older than genes of the examined caprines and indicates it followed an independent evolution after separating from species having the same HBBA locus. Similarly, phylogenetic analyses of β-globin chain sequences suggest a different evolution for globins coded by the HBBA locus with respect to the HBBB. Ammotragus β-globin chain shows all the amino acids responsible for the low oxygen affinity of ruminant Hbs. Investigations on the oxygen transport properties indicate that the intrinsic oxygen affinity of aoudad Hb is higher than the Hb B of the domestic sheep and, at the same time, more similar to that of other A type Hbs, whereas in the presence of the Cl− effector the oxygen affinity is approximately the same as that of the other species.