Functional properties of the newly observed Gγ-chain fetal hemoglobin variant Hb F-Monserrato-Sassari (HBG2:c.280T > C) or [ Gγ93 (F9) Cys → Arg]

• Published in: Biochimica et biophysica acta. General subjects Vol. 1810; no. 12; pp. 1272 - 1277
• Main Authors: Pellegrini, Mariagiuseppina, Manconi, Barbara, Olianas, Alessandra, Sanna, Maria Teresa, Meloni, Claudia, Pirastru, Monica, Mereu, Paolo, Leoni, Giovanni, Masala, Bruno, Manca, Laura
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2011
• Subjects: amino acid substitution; amino acids; blood; electrophoresis; electrospray ionization mass spectrometry; Gene sequencing; genes; Gγ globin gene; HbF variant; hemoglobin; neonates; nitric oxide; NO transport; oxygen; Oxygen affinity; surveys; α1γ2 interface; FPLC; Mav; HbA; α1γ2 interface; AUT-PAGE; ESI-MS; Oxygen affinity; IEF; HbF; NO transport; P 50; Gene sequencing; RP-HPLC; CE-HPLC; BPG; HbF variant; Gγ globin gene; PCR; n 50
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/j.bbagen.2011.06.007

HbF-Monserrato-Sassari is a newly discovered abnormal fetal hemoglobin observed in an apparently normal newborn baby during a hemoglobinopathies survey at birth in North Sardinian population. Electrophoretic analysis of the cord blood lysate evidenced for an abnormal tetramer due to a mutated fetal globin chain. Electrospray ionisation-mass spectrometry and gene sequencing were used to identify the mutation. Oxygen binding ability of the variant Hb was determined. Sequencing of the γ globin genes revealed the TGT → CGT transition at codon 93 in one of the two Gγ genes, which leads to the Arg for Cys amino acid replacement at position 9 of the F α-helix. The amino acid substitution was confirmed by mass spectrometric analysis of the globin chains. Since modifications or substitutions at position β93 are known to affect the arrangement of a salt bridge at the α1β2 sliding contacts that are crucial for subunit cooperativity, the functional properties of the variant were studied to evaluate the effect of the replacement at the same position in the γ globin chain. With respect to normal HbF, the variant showed a significant increase in oxygen affinity and a slight decrease of both Bohr effect and cooperativity. Result indicates a key role of the Cys γ93 residue for subunit cooperativity in the T → R transition of the HbF tetramer. Substitutions at the F9 position of the Gγ globin may result in stabilization of the high affinity R-state of the Hb tetramer. Because of the loss of Cys γ93 residue, this variant is considered to be potentially compromised in nitric oxide transport. ► HbF-Monserrato-Sassari is a newly discovered abnormal human fetal hemoglobin. ► It is characterized by the Arg for Cys replacement at position 93 of the Gγ globin. ► It shows increased oxygen affinity, slightly decreased Bohr effect and cooperativity. ► Cys γ93 has a key role for subunit cooperativity in the T → R transition of the HbF. ► Substitutions at this position may stabilize the high affinity R-state of the Hb and endanger nitric oxide transport.