Structure and function of sheep hemoglobin Chios: A novel allele at the HBBB locus with two Lys -> Arg substitutions at positions beta 66(E10) and beta 144(HC1)

A novel hemoglobin variant was observed in pure sheep (Ovis aries) breeds of the island of Chios (Greece), Egypt and Hungary. This silent variant was identified by gel electrophoresis and RP-HPLC of dissociated globin chains. Two Arg for Lys substitutions were detected, by means of MALDI TOF electrospray mass spectrometric analysis for the intact globins, at positions beta 66(E10) and beta 144(HCl) of a globin chain having the sequence of the beta(B) chain. Sequencing of the beta-globin gene confirmed the variant gene as being an allele of the HBBB locus having the AAG -> AGG and the AAA -> AGA mutations at codons 66 and 144, respectively, both corresponding to the Lys -> Arg substitution. The intrinsic oxygen affinity of the variant Hb (logP(50) = 0.79 at pH 7.0) was found to be intermediate between that of the sheep Hb B (logP(50) = 0.92) and that of Cypriot mouflon (O. a. ophion) Hb (logP(50) = 0.53), the latter having only the Lys -> Arg change at beta 144, whereas nearly no differences were observed in the presence of the Cl- physiological effector. Result supports the indication that Arg at beta 144 enhances the role of the ligand in decreasing oxygen affinity, this effect being partially counteracted when Arg is at beta 66. Data also shows that the Lys -> Arg change at beta 66 is responsible for 1.49 fold reduction in the intrinsic oxygen affinity. This hitherto undescribed variant increases to seven the number of alleles at the sheep HBBB locus. Following the nomenclature used for human Hb variants, the new allele was termed as the Hb Chios or [beta(B)66(E10) Lys -> Arg, 144(HCl)Lys -> Arg], whereas the proposed genetic nomenclature of the locus is HBB