Hemoglobin Milledgeville (alpha 44 (CD2) Pro leads to Leu): a new variant with increased oxygen affinity

Hematological Characterizations and Molecular Diagnostic Aspects of Hb Wiangpapao [α44(CE2)Pro→Ser (α1), CCG>TCG; HBA1: c.133C>T], a New α-Globin Variant Found in a Pregnant Thai Woman

We report the hematological parameters and provide a rapid molecular analysis method for detection of Hb Wiangpapao [α44(CE2)Pro→Ser, CCG>TCG; HBA1: c.133C>T], a new α-globin variant found in a pregnant Thai woman. Her red cell indices were measured by an automated blood counter. The results were: red blood cell (RBC) count 4.03 × 10¹²/L, Hb 13.1 (g/dL), packed cell volume (PCV) 0.39 L/L, mean corpuscular volume (MCV) 97.0 fL, mean corpuscular hemoglobin (Hb) (MCH) 32.5 pg, mean corpuscular Hb concentration (MCHC) 33.4 g/dL, and RBC distribution width (RDW) 9.4%. The Hb typing by high performance liquid chromatography (HPLC) showed 13.6% abnormal Hb at a retention time of 2.20 min. that was difficult to distinguish from Hb A. On the capillary electrophoresis (CE) electropherogram, this hemoglobinopathy peak did not separate from the Hb A peak. DNA sequencing showed a C>T transition at the first position of codon 44 (CCG>TCG) of the α1-globin gene that led to a substitution of proline for serine. This mutation has not been recorded in the public databases. Therefore, we named it Hb Wiangpapao as it was first discovered in the Wiangpapao District, Chiang Rai, Thailand. The multiplex allele-specific polymerase chain reaction (ASPCR) for detection of Hb Wiangpapao was developed and revealed a 510 bp specifically amplified fragment. The better understanding of hematological characterizations and the newly developed multiplex ASPCR for diagnosis of Hb Wiangpapao are useful for genetic counseling and family education.

Familial secondary erythrocytosis due to increased oxygen affinity is caused by destabilization of the T state of hemoglobin Brigham (α₂β₂(Pro100Leu))

Hemoglobin Brigham (β Pro100 to Leu) was first reported in a patient with familial erythrocytosis. Erythrocytes of an affected individual from the same family contain both HbA and Hb Brigham and exhibit elevated O₂ affinity compared with normal cells (P₅₀ = 23 mm Hg vs. 31 mmHg at pH 7.4 at 37°C). O₂ affinities measured for hemolysates were sensitive to changes in pH or chloride concentrations, indicating little change in the Bohr and Chloride effects. Hb Brigham was separated from normal HbA by nondenaturing cation exchange liquid chromatography, and the amino acid substitution was verified by mass spectrometry. The properties of Hb Brigham isolated from the patient's blood were then compared with those of recombinant Hb Brigham expressed in Escherichia coli. Kinetic experiments suggest that the rate constants for ligand binding and release in the high (R) and low (T) affinity quaternary states of Hb Brigham are similar to those of native hemoglobin. However, the Brigham mutation decreases the T to R equilibrium constant (L) which accelerates the switch to the R state during ligand binding to deoxy-Hb, increasing the rate of association by approximately twofold, and decelerates the switch during ligand dissociation from HbO₂, decreasing the rate approximately twofold. These kinetic data help explain the high O₂ affinity characteristics of Hb Brigham and provide further evidence for the importance of the contribution of Pro100 to intersubunit contacts and stabilization of the T quaternary structure.

Structure of the altitude adapted hemoglobin of guinea pig in the R2-state

BACKGROUND

Guinea pigs are considered to be genetically adapted to a high altitude environment based on the consistent finding of a high oxygen affinity of their blood.

METHODOLOGY/PRINCIPAL FINDINGS

The crystal structure of guinea pig hemoglobin at 1.8 A resolution suggests that the increased oxygen affinity of guinea pig hemoglobin can be explained by two factors, namely a decreased stability of the T-state and an increased stability of the R2-state. The destabilization of the T-state can be related to the substitution of a highly conserved proline (P44) to histidine (H44) in the alpha-subunit, which causes a steric hindrance with H97 of the beta-subunit in the switch region. The stabilization of the R2-state is caused by two additional salt bridges at the beta1/beta2 interface.

CONCLUSIONS/SIGNIFICANCE

Both factors together are supposed to serve to shift the equilibrium between the conformational states towards the high affinity relaxed states resulting in an increased oxygen affinity.

Hb south Milwaukee [beta 105 (G7) Leu----Phe]: a newly-identified hemoglobin variant with high oxygen affinity

Fifteen individuals among four generations of a family of English ancestry demonstrated elevated hemoglobin levels accompanied by leftward-shifted whole blood oxygen equilibrium curves. Five of the affected family members have required phlebotomies for relief of symptoms attributable to erythrocytosis. An abnormal hemoglobin or globin chain could not be isolated, but 43% of the beta chains of the affected individuals contained a Leu----Phe substitution at position 105 (G7). Oxygen equilibrium curves demonstrated a normal Bohr effect but decreased cooperativity.

Hemoglobin Nouakchott [alpha 114(GH2)Pro----Leu]: a new hemoglobin variant displaying an unusual increase in hydrophobicity

The most striking fact in Hb Nouakchott [alpha 114(GH2)Pro----Leu] is the highly increased hydrophobicity of the abnormal chain. In comparison to other variants carrying the same amino-acid substitution, but at another position, the involvement of the environmental domains in the expression of the hydrophobicity is shown. Even though the substitution concerned a proline residue, it was without consequences on the oxygen binding and the stability of the molecule.

Hb Warsaw (beta 42 Phe----Val): an unstable hemoglobin with decreased oxygen affinity. I. Hematologic and clinical expression

Four members in two generations of a Polish-American family exhibited findings of congenital Heinz-body hemolytic anemia accompanied by cyanosis. Two of the affected family members have also developed severe pulmonary hypertension, with a fatal outcome in one of them. Blood from the affected individuals showed decreased oxygen affinity and contained elevated levels of methemoglobin. An unstable hemoglobin fraction underwent rapid precipitation following exposure of the red cell lysates to isopropyl alcohol or heat. This hemoglobin contained a newly identified abnormal beta chain with an amino acid substitution at the same position as that of Hb Hammersmith and Hb Bucuresti-Louisville.