A new hemoglobin variant, hemoglobin Nunobiki [alpha 141 (HC3) Arg----Cys]. Notable influence of the carboxy-terminal cysteine upon various physico-chemical characteristics of hemoglobin

Molecular Characterization of α- and β-Thalassemia Among Children Less Than 18 Years Old in Guizhou, China

BACKGROUND

Thalassemia is an inherited hemolytic disease, the complications and sequelae of which have posed a huge impact on both patients and society. But limited studies have investigated the molecular characterization of α- and β-thalassemia in children from Guizhou, China.

METHODS

Between January 2019 and December 2022, a total of 3301 children, aged 6 months to 18 years, suspected of having thalassemia underwent molecular analysis.

RESULTS

Out of the total sample, 824 (25%) children were found to carry thalassemia mutations. The carrier rates of α-thalassemia, β-thalassemia, and α + β-thalassemia were determined as 8.1%, 15.6%, and 1.3%, respectively. Approximately 96.5% of the α-thalassemia gene mutations were --SEA (51%), ααCS (20.9%), -α3.7 (19.6%), and -α4.2 (5.0%). The most prevalent mutations of β-thalassemia were βCD17(A>T) (41.5%), βCD41-42(-TTCT) (37.7%), and βIVS-II-654(C>T) (11.3%). Additionally, we identified rare cases, including one case with ααHb Nunobiki/αα, two cases with triplicated α-thalassemia (one case with ααα/ααα and βCD41-42/βN and the other with ααα-3.7/αα and βE CD26/βN), and also one case with α Q-Thailandα/-α4.2 and βCD41-42/βN.

CONCLUSIONS

Our study findings provide important insights into the heterogeneity of thalassemia carrier rates and molecular profiles among children in the Guizhou region. The findings support the development of prevention strategies to reduce the incidence of severe thalassemia in the future.

Hemoglobin function and allosteric regulation in semi-fossorial rodents (family Sciuridae) with different altitudinal ranges

Semi-fossorial ground squirrels face challenges to respiratory gas transport associated with the chronic hypoxia and hypercapnia of underground burrows, and such challenges are compounded in species that are native to high altitude. During hibernation, such species must also contend with vicissitudes of blood gas concentrations and plasma pH caused by episodic breathing. Here, we report an analysis of hemoglobin (Hb) function in six species of marmotine ground squirrels with different altitudinal distributions. Regardless of their native altitude, all species have high Hb-O2 affinities, mainly due to suppressed sensitivities to allosteric effectors [2,3-diphosphoglycerate (DPG) and chloride ions]. This suppressed anion sensitivity is surprising given that all canonical anion-binding sites are conserved. Two sciurid species, the golden-mantled and thirteen-lined ground squirrel, have Hb-O2 affinities that are characterized by high pH sensitivity and low thermal sensitivity relative to the Hbs of humans and other mammals. The pronounced Bohr effect is surprising in light of highly unusual amino acid substitutions at the C-termini that are known to abolish the Bohr effect in human HbA. Taken together, the high O2 affinity of sciurid Hbs suggests an enhanced capacity for pulmonary O2 loading under hypoxic and hypercapnic conditions, while the large Bohr effect should help to ensure efficient O2 unloading in tissue capillaries. In spite of the relatively low thermal sensitivities of the sciurid Hbs, our results indicate that the effect of hypothermia on Hb oxygenation is the main factor contributing to the increased blood-O2 affinity in hibernating ground squirrels.

Characterization of the elusive disulfide bridge forming human Hb variant: Hb Ta-Li beta83 (EF7)Gly --> Cys by electrospray mass spectrometry

An electrospray mass spectrometric approach to the identification of a human hemoglobin (Hb) variant involving a Cys residue incorporation is presented. In Hb Ta-Li (beta83Gly --> Cys), Cys83 forms inter-molecular disulfide bridges. Routine analysis of the denatured Hb showed the presence of a minor beta chain variant whose mass apparently was 1 Da less than the expected mass difference of 46 Da for a Gly --> Cys substitution. Reduction of the globin chains with dithiothreitol gave an intense monomer with the expected mass difference for the Gly --> Cys substitution. After reprocessing the original raw data from the denatured Hb and taking into account the possibility of dimer formation, a component was revealed whose mass was consistent with a disulfide linked dimer of Ta-Li beta globins. The mutation was localized to peptide betaT10 by analysis of a tryptic digest. Tandem mass spectrometry and DNA sequencing confirmed the Gly --> Cys substitution occurred at residue 83 of the beta chain. Problems encountered in identifying the components in mixtures of monomers and dimers are discussed.

Hemoglobin Porto Alegre forms a tetramer of tetramers superstructure

The effects of the mutation beta9(A6)Ser --> Cys on the interactions between the human hemoglobin molecules were investigated, and comparisons were made with other variants having an additional cysteine residue. In hemoglobin Porto Alegre (PA), the beta9 mutation induces polymerization by forming interchain disulfide bonds via the extra cysteine. The hemolysate from a heterozygote was separated by gel filtration into a tetrameric fraction and a higher-molecular-weight oligomeric fraction (30%). Reversed-phase high-performance liquid chromatography and electrospray ionization mass spectrometry (ESI-MS) under denaturing conditions showed that the tetrameric fraction contained only normal alpha- and beta-chains, whereas the oligomeric fraction contained only normal alpha-chain and disulfide-linked beta(PA) dimer. Under native conditions, ESI-MS of the oligomeric fraction revealed a principal complex of mass 258,400 Da corresponding to a tetramer of tetramers, and 10% of minor components. Transmission electron microscopy corroborated this structure by showing four spheres of 140 A diameter surrounding a central cavity. Equilibrium experiments on the oligomer at different concentrations, using gel filtration and dimer exchange experiments with metHbA-CN, showed that the tetramer of tetramers dissociates into smaller species, probably by breaking the dimer-dimer allosteric interface. None of the other variants investigated formed such a large oligomer.

Hb Fukutomi [alpha 126(H9)Asp----Val]: a new hemoglobin variant with high oxygen affinity

Hb Fukutomi [alpha 126(H9)Asp----Val], a new hemoglobin variant with a high affinity for oxygen (log P50 = 0.201 at pH 7.0, normal = 1.087) was detected in a Japanese male during a screening survey. The amino acid substitution is located in the alpha 1 beta 1 contact of the tetramic molecule. Like other variants of the high oxygen affinity type Hb Fukutomi showed increased resistance to auto-oxidation. The tryptic peptide alpha T-13, that usually forms part of the trypsin-resistant core of the alpha chain, was cleaved off by trypsin in the new variant and released into the soluble fraction.

Contribution of arginine (HC3) 141 alpha to the Bohr effect of the fourth binding step in the reaction of ligand with human hemoglobin

A few years ago we reported that histidine (HC3) 146 beta plays a major role in the pH-dependent properties of the R-state of human hemoglobin, accounting for close to 50% of the R-state Bohr effect. We have extended these studies by examining the role of arginine 141 alpha, another group known to affect the overall Bohr effect. We have compared the pH dependencies of the rate constants for the dissociation and combination of the fourth carbon monoxide molecule, l4 and l'4, respectively, for native hemoglobin A (HbA) and a control reconstituted HbA, and des-(Arg 141 alpha) HbA, the hemoglobin molecule resulting from the enzymatic removal of the C-terminal arginine of the alpha-chain of human Hb. From these kinetic constants the pH dependence of L4, the affinity constant for the fourth carbon monoxide molecule, has been estimated. We find that the removal of arginine 141 alpha reduces the pH dependence of log L4 by about 80% between pH 6 and 8, where the alkaline Bohr effect normally occurs. The sum of the effects of the removal of His 146 beta and of Arg 141 alpha is greater than 100%. This suggests that at least one of these modifications alters the contributions of other residues of this Bohr effect.

Hb Mississippi [beta 44(CD3)Ser----Arg]: a new variant with anomalous properties

Hb Mississippi was discovered in a 6-year-old Chinese girl with chronic anemia and thalassemia intermedia. Family studies revealed that she had inherited the Hb Mississippi from her father as well as inheriting a gene for beta+-thalassemia from her mother. Electrophoretic analyses of the hemolysate of the father of the father and the proband on polyacrylamide gels at pH 8.6 showed that the abnormal hemoglobin had three distinct mobilities. A similar pattern was also observed by isoelectricfocusing. In addition, multiple abnormal peaks were observed by high performance liquid chromatographic hemoglobin separations as well as high performance liquid chromatographic globin chain separation. Structural analysis of the abnormal hemoglobin demonstrated a single abnormality; the substitution of serine to cysteine at position 44 (CD3) of the beta-globin chain. Since CD3 is on the surface of the beta-globin chain, it was thought that polymerization of the abnormal hemoglobin by disulfide linkages might have been responsible for the anomalous behavior on electrophoresis and high performance liquid chromatography. Gel filtration chromatography on G-200 Sephadex confirmed this supposition and demonstrated that the abnormal globin chain polymerized with itself as well as with other globin chains.