Hemoglobin J Singapore: alpha 78 Asn--Asp; alpha 79 Ala--Gly

A New Hemoglobin Variant: Hb Tangshan [HBA1: c.239C > T, CD79(GCG > GTG)(Ala > Val)] Detected by MALDI-TOF MS

In this report we decribed a new α-chain variant found during the measurement of hemoglobin A1c (Hb A1c) using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS). MALDI-TOF MS analysis detected an α-chain variant with a mass of 15,155 Da. However, this Hb variant was not detected during Hb A1c measurement by cation-exchange high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) methods. Sanger sequencing validated the presence of a heterozygous missense mutation [HBA1: c.239C > T, CD79(GCG > GTG)(Ala > Val)]. The observed 28 Da mass difference exactly matches the theoretical mass difference (28 Da) resulting from the substitution of alanine (89.079) with valine (117.133). As this represents the initial documentation of the mutation, we named it Hb Tangshan after the proband's residence.

Application of Targeted Next-Generation Sequencing for the Investigation of Thalassemia in a Developing Country: A Single Center Experience

Thalassemia is identified as a prevalent disease in Malaysia, known to be one of the developing countries. Fourteen patients with confirmed cases of thalassemia were recruited from the Hematology Laboratory. The molecular genotypes of these patients were tested using the multiplex-ARMS and GAP-PCR methods. The samples were repeatedly investigated using the Devyser Thalassemia kit (Devyser, Sweden), a targeted NGS panel targeting the coding regions of hemoglobin genes, namely the HBA1, HBA2, and HBB genes, which were used in this study. There were many different genetic variants found in 14 unrelated cases. Out of all fourteen cases, NGS was able to determine an additional -50 G>A (HBB:c.-100G>A) that were not identified by the multiplex-ARMS method, including HBA2 mutations, namely CD 79 (HBA2:c.239C>G). Other than that, CD 142 (HBA2:c.427T>C) and another non-deletional alpha thalassemia and alpha triplication were also not picked up by the GAP-PCR methods. We illustrated a broad, targeted NGS-based test that proposes benefits rather than using traditional screening or basic molecular methods. The results of this study should be heeded, as this is the first report on the practicality of targeted NGS concerning the biological and phenotypic features of thalassemia, especially in a developing population. Discovering rare pathogenic thalassemia variants and additional secondary modifiers may facilitate precise diagnosis and better disease prevention.

Hb Southern Italy: coexistence of two missence mutations (the Hb Sun Prairie alpha2 130 Ala --> Pro and Hb Caserta alpha2 26 Ala --> Thr) in a single HBA2 gene

This study describes a new molecular condition in the alpha(2)-globin gene (HBA2) found in six unrelated families from Southern Italy (Campania and Sicily). This new double mutant form of haemoglobin is called Hb Southern Italy and originated from the coexistence of two known mutations occurring in the same globin gene, HBA2 26 G-->A (Hb Caserta) and HBA2 130 G-->C (Hb Sun Prairie). Hb Sun Prairie was originally observed in Indian patients in either the homozygous state, with severe hemolytic anemia, and in the heterozygous state with microcytosis, or in asymptomatic cases as an alpha-thalassemia carrier phenotype. Hb Caserta was observed for the first time in a Casertian family (South Italy) that displayed a slowmigrating haemoglobin upon investigation. We report the clinical phenotype and molecular study of this new double mutant form of haemoglobin in heterozygous and homozygous subjects, as well as in association with alpha degrees delectional thalassemia.

Prediction of protein deamidation rates from primary and three-dimensional structure

A method for the quantitative estimation of instability with respect to deamidation of the asparaginyl (Asn) residues in proteins is described. The procedure involves the observation of several simple aspects of the three-dimensional environment of each Asn residue in the protein and a calculation that includes these observations, the primary amino acid residue sequence, and the previously reported complete set of sequence-dependent rates of deamidation for Asn pentapeptides. This method is demonstrated and evaluated for 23 proteins in which 31 unstable and 167 stable Asn residues have been reported and for 7 unstable and 63 stable Asn residues that have been reported in 61 human hemoglobin variants. The relative importance of primary structure and three-dimensional structure in Asn deamidation is estimated.

Copper(II)-induced conformational changes and protease resistance in recombinant and cellular PrP. Effect of protein age and deamidation

While PrP(C) rearranges in the area of codons 104-113 to form PrP(Sc) during prion infections, the events that initiate sporadic Creutzfeldt-Jakob disease are undefined. As Cu(II) is a putative ligand for PrP(C) and has been implicated in the pathogenesis of Creutzfeldt-Jakob disease and other neurodegenerative diseases, we investigated the structural effects of binding. Incubation of brain microsomes with Cu(II) generated approximately 30-kDa proteinase K-resistant PrP. Cu(II) had little effect on fresh recombinant PrP23-231, but aged protein characterized by conversion of Asn-107 to Asp decreased alpha-helical content by approximately 30%, increased beta-sheet content 100%, formed aggregates, and acquired proteinase K resistance in the presence of Cu(II). These transitions took place without need for acid pH, organic solvents, denaturants, or reducing agents. Since conversion of Asn to Asp proceeds by a spontaneous pathway involving deamidation, our data suggest that covalent variants of PrP(C) arising in this manner may, in concert with Cu(II), generate PrP(Sc)-like species capable of initiating sporadic prion disease.

Hb Osler [beta 145(HC2)Tyr-->Asp] results from posttranslational modification

We studied two members of an African American family with erythrocytosis. An abnormal hemoglobin variant with an electrophoretic pattern on cellulose acetate similar to Hb J was identified. The oxygen dissociation curve using whole blood was biphasic, dramatically left-shifted, and hyperbolic. Sequence analysis of DNA from the proband showed heterozygosity for a T-->A change at the first position of codon 145 in the beta-globin gene which results in the substitution of an asparagine residue for normal tyrosine. The second cycle of C-terminal amino acid sequence analysis of a mixture of alpha- and beta-globin chains showed tyrosine, aspartic acid, and small amounts of asparagine. Collectively, these results indicate the existence of a mutation at codon 145 of the beta-globin gene which encodes for asparagine instead of tyrosine, and that asparagine then undergoes a partial posttranslational deamidation to aspartic acid. This amino acid substitution corresponds to Hb Osler, which is a high oxygen affinity hemoglobin variant, initially described to be caused by a substitution of Tyr-->Asp at beta 145. Posttranslational amino acid modification may constitute an important component in the pathophysiology of hemoglobinopathies.

Hemoglobin S/hemoglobin Osler: a case with 3 beta globin chains. DNA sequence (AAT) proves that Hb Osler is beta 145 Tyr-->Asn

A 13-year-old African-American female with erythrocytosis and three different beta globins on electrophoresis beta A, beta S, and beta Osler, raised the possibility that one chromosome 11 might contain a duplicated beta globin gene, since there are normally only 2 beta globin genes. DNA sequence analysis showed GTG at codon 6 in exon 1, corresponding to Hb S and AAT at codon 145 in exon 3, indicating a substitution of Asn for Tyr. Thus, Hb Osler undergoes spontaneous post-translational deamidation, beta 145 Asn-->beta 145 Asp. Unmodified Hb Osler (Asn) co-migrates with Hb A on electrophoresis and co-elutes with Hb A on HPLC; therefore it has not been identified previously. All previous studies have incorrectly identified the mutation as being beta 145 (HC 2) Tyr-->Asp.

Structure of the EF corner favors deamidation of asparaginyl residues in hemoglobin: the example of Hb La Roche-sur-Yon [beta 81 (EF5) Leu----His]

Some abnormal hemoglobins constitute models which allow one to evaluate the structural requirements for post-translational modifications in proteins, such as deamidation. Hb La Roche-sur-Yon [beta 81 (EF5) Leu----His] is an unstable hemoglobin variant displaying a moderately increased oxygen affinity. About half of the abnormal hemoglobin, in addition to the substitution at position beta 81, carries a deamidation of the neighboring asparagine residue, beta 80 (EF4). The histidine at position beta 81 cannot fit into the small hydrophobic pocket which normally accomodates the leucine residue. This structural change opens the heme pocket and modifies the general conformation of the EF segment, thus explaining the increase in oxygen affinity and the achievement of a three-dimensional structure favoring asparagine deamidation. Histidine beta 81 could also act as a catalyst in the deamidation reaction. Deamidation has already been reported for two other variants of the EF corner, Hb Providence [beta 82 (EF6) Lys----Asn] and Hb J Singapore [alpha 79 (EF8) Ala----Gly]. In all these cases it seems that a histidine may catalyze the deamidation of the asparagine residues and that disturbing the folding of the EF corner will provide an extra flexibility favoring the reaction.

Nonenzymatic deamidation of asparaginyl and glutaminyl residues in proteins

Some asparagine and glutamine residues in proteins undergo deamidation to aspartate and glutamate with rates that depend upon the sequence and higher-order structure of the protein. Functional groups within the protein can catalyze this reaction, acting as general acids, bases, or stabilizers of the transition state. Information from specific proteins that deamidate and analysis of protein sequence and structure data bases suggest that asparagine and glutamine lability has been a selective pressure in the evolution of protein sequence and folding. Asparagine and glutamine deamidation can affect protein structure and function in natural and engineered mutant sequences, and may play a role in the regulation of protein folding, protein breakdown, and aging.

Structural and functional studies of hemoglobin Poissy alpha 2 beta 2(56) (D7) Gly----Arg and 86 (F2) Ala----Pro

Hemoglobin Poissy alpha 2 beta 2(56) (D7) Gly----Arg and 86 (F2) Ala----Pro, is a new variant of the beta chain with two substitutions within the second exon of the corresponding gene. The electrophoretic mobilities are identical to those of Hb Hamadan alpha 2 beta 2(56) (D7) Gly----Arg as is the fingerprint of the tryptic hydrolysate of the two abnormal beta chains. The second substitution beta 86 Ala----Pro was detected by high-pressure liquid chromatography. Hb Poissy has a threefold increase in oxygen affinity with low Hill coefficient and diminished Bohr effect, which are restored to normal upon addition of 2,3-bisphosphoglycerate. Since the functional properties of Hb Hamadan (beta 56 Gly----Arg) have been described as normal, the abnormal function of Hb Poissy may be attributed to the beta 86 (F2) Ala----Pro substitution. Hb Poissy exhibits a mild instability and a greater reactivity of the thiol groups of the beta 93 (F9) Cys residues in the deoxy form than does Hb A. The oxidation rate of Hb Poissy is biphasic indicating a large inequivalence between the alpha and beta hemes. Thereafter NMR studies demonstrated that the beta 86 Ala----Pro substitution produces a displacement of the F helix closer to the heme plane and a large increase in the dynamic fluctuations of the tertiary structure on the proximal side of the beta hemes. These results lead to the conclusion that the beta 86 Ala----Pro substitution produces a destabilization of the F helix extending downwards to the FG corner and altering both the beta hemes and the alpha 1 beta 2 contacts.

Hb J-Singa (alpha-78 Asn leads to Asp), a newly discovered hemoglobin variant with the same amino acid substitution as one of the two present in Hb J-Singapore (alpha-78 Asn leads to, alpha-79 Ala leads to Gly)

A new fast-moving alpha-chain Hb variant with an Asn leads to Asp substitution at position alpha-78 was found in a French-Acadian family living in Eastern Canada. The identical substitution was reported in Hb J-Singapore, which also had an additional Ala leads to Gly substitution at position alpha-79. The new variant, which did not result in any clinical symptoms, was named accordingly, Hb J-Singa.

Hemoglobin Arlington Park. A new hemoglobin variant with two amino acid substitutions in the beta chain

Hemoglobin Arlington Park was detected accidentally as result of the use of a hemolysate which contained hemoglobin with normal electrophoretic mobility as a control for peptide mapping. Peptide maps of this hemolysate revealed 3 new peptides resulting from 2 amino acid substitutions to give to new variant with the composition (beta6 Glu replaced by Lys, 95 Lys replaced by Glu).