[The conformational dynamic of the tetramer hemoglobin molecule as revealed by hydrogen exchange. II. Influence of the intersubunit contact splitting].

The rate of the H-D exchange of the peptide NH atoms of the isolated alpha and beta subunits of human Hb were studied at the pH range 5.5-9.0 and 20 degrees C by the IR spectroscopy. The factor retardation of the exchange rate of subunits -P in the range -10(2)-10(7). In comparison with tetramer Hb the probability of local fluctuations (1/P) is increased to a slightly greater extent for the monomeric alpha subunits then for the tetramer beta subunits. Unlike Hb oxygenation of subunits does not influence on the probability of the local fluctuations and subunits have no the pH-dependent change of the value 1/P observable for the ligand Hb. The possible mechanisms of the overall intensification of the local fluctuations upon the splitting of the Hb tetrameric contacts between subunits are discussed with the inviting of the structural crystallographic data.

Access to a syllabus of human hemoglobin variants (1996) via the World Wide Web.

Information on mutations in human hemoglobin is important in many efforts, including understanding the pathophysiology of hemoglobin diseases, developing therapies, elucidating the dynamics of sequence alterations inhuman populations, and dissecting the details of protein structure/function relationships. Currently, information is available on a large number of mutations and variants, but is distributed among thousands of papers. In an effort to organize this voluminous data set, two Syllabi have been prepared compiling succinct information on human hemoglobin abnormalities. In both of these, each entry provides amino acid and/or DNA sequence alterations, hematological and clinical data, methodology used for characterization, ethnic distribution, and functional properties and stability of the hemoglobin, together with appropriate literature references. A Syllabus of Human Hemoglobin Variants (1996) describes 693 abnormal hemoglobins resulting from alterations in the alpha-, beta-, gamma-, and delta-globin chains, including special abnormalities such as double mutations, hybrid chains, elongated chains, deletions, and insertions. We have converted this resource to an electronic form that is accessible via the World Wide Web at the Globin Gene Server (http://globin.cse.psu.edu). Hyperlinks are provided from each entry in the tables of variants to the corresponding full description. In addition, a simple query interface allows the user to find all entries containing a designated word or phrase. We are in the process of converting A Syllabus of Thalassemia Mutations (1997) to a similar electronic format.

Analysis of mRNA from red cells of patients with thalassemia and hemoglobin variants.

During the past decade new procedures have been developed for the isolation of RNA from a few mL of freshly collected blood. This material is reverse transcribed and the resulting cDNA can be used for the determination of the ratios between different types of globin mRNA, namely alpha 2/alpha 1, alpha/zeta, alpha/beta, gamma/beta, beta A/beta X, delta beta Lep/beta, and G gamma/A gamma. Details about these polymerase chain reaction-based methods are reviewed, and information about their usefulness in studying alpha-thalassemia, beta-thalassemia, sickle cell anemia and other beta-globin gene abnormalities, Hb Lepore heterozygosity, and heterozygosity for alpha 2- or alpha 1-globin gene mutations will be provided. The methods are also most useful in characterizing the mRNA types in single, in vitro cultured, BFU-E colonies; in colonies derived from cells of a Hb S heterozygote; for instance, the beta A- and beta(S)-mRNAs were present in all colonies and in about equal quantities, while many of those cells from a subject with a somatic cell mutant (Hb Costa Rica) contained beta A-mRNA and no beta-Costa Rica mRNA, and only a few had both types. The techniques described have considerable diagnostic value and offer a rather simple approach to the study of some of the listed diseases.

The importance of the 3' untranslated region for the expression of the alpha-globin genes.

With a reverse transcription-polymerase chain reaction procedure, we have determined the relative quantities of alpha 2- and alpha 1-mRNA in several patients with heterozygosities for alpha 2- or alpha 1-globin gene mutations, in subjects with two forms of alpha-thalassemia-2 (-3.7 kb; -4.2 kb), and in two children with an alpha-globin gene triplication. Mutations in either one of the two genes do not affect the mRNA production, and the alpha 2- to alpha 1-mRNA ratios in our heterozygotes are the same (approximately 2.7) as in normal persons with four alpha-globin genes, while the alpha/alpha X ratios of approximately 1.7 for alpha 2 variants and of approximately 6.2 for alpha 1 variants agree with the theoretic values. The deletion of 3.7 kb (leading to the formation of the alpha 2 alpha 1 hybrid gene) and of 4.2 kb (resulting in the presence of only the alpha 1 gene) causes the alpha 2/alpha 1 ratio to decrease to approximately 1.7, indicating that both are expressed as an alpha 1 gene. Data obtained for an Hb G-Philadelphia heterozygote (alpha alpha/-alpha G) show that the alpha 2 alpha 1 hybrid gene produces approximately 30% less mRNA than an alpha 1-globin gene on a normal chromosome, which may be caused by loss of some sequences 3' to the alpha 2 gene. The same may be the case for the alpha 1-globin gene on the chromosome with the 4.2 kb alpha-thal-2 deletion. These results suggest an important role for sequences located 3' to the terminating codon in regulating transcription. Support for this hypothesis was obtained from data for the two children with an alpha-globin gene triplication; the high alpha 2/alpha 1-mRNA ratio can be explained by assuming that the alpha 1 alpha 2 hybrid gene of the alpha 2(alpha 1 alpha 2)alpha 1 triplication expresses as an alpha 2 gene.

A second, elongated, alpha 2-globin mRNA is present in reticulocytes from normal persons and subjects with terminating codon or poly A mutations.

With an RT-PCR procedure we have identified a second, elongated, alpha 2-globin mRNA in reticulocytes of normal persons and of patients with alpha-thal, particularly those with mutations in the terminating codon (TAA-->CAA; Hb Constant Spring; TAA-->TAT, Hb Paksé) or in the poly A site (AATAAA-->AATAAG). This type of mRNA is elongated because a result a cryptic poly A site 1048 bp past the terminating codon is used. Even some 5% of the alpha 2-mRNA of normal persons is of the elongated type. Quantitative data suggest high levels of this mRNA in heterozygous and homozygous carriers of poly A mutations and low levels in patients with the terminating codon mutations. Hematological and Hb data suggest that translation of these elongated mRNAs is minimal. No elongated alpha 1-mRNA has been observed.

Hb Bibba or alpha 2 136(H19)Leu-->Pro beta 2 in a Caucasian family from Alabama.

Several members of a large Caucasian family who presented with a congenital Heinz body hemolytic anemia were found to be carriers of the unstable Hb Bibba or alpha 2 136(H19)Leu-->Pro beta 2. Identification by protein analysis was hampered by the instability of the variant which complicated its isolation from shipped blood samples. Moreover, the detection of the CTG-->CCG mutation at codon 136 of the alpha 2 gene required the substitution of dGTP by dITP during the DNA sequencing process to prevent the occurrence of secondary structures and compressions in the sequencing gel. The first Hb Bibba heterozygote, characterized in 1968 (1), is believed to be a member of this family. The clinical expression of the disease is surprisingly variable.

Compound heterozygosity for two alpha-globin gene defects, Hb Taybe (alpha 1; 38 or 39 minus Thr) and a poly A mutation (alpha 2; AATAAA-->AATAAG), results in a severe hemolytic anemia.

We have identified two alpha-globin gene variations in an Arabian male with severe hemolytic disease through sequencing of amplified DNA of his alpha 2- and alpha 1-globin genes. One of the abnormalities involves a CAC (ACC or CCA) deletion between codons 36 and 41 of the alpha 1-globin gene. This leads to the synthesis of an abnormal alpha chain with one instead of two threonine residues at positions 38-39 and to the formation of the unstable Hb Taybe. The second variation is a mutation located in the poly A site of the alpha 2-globin gene (AATAAA-->AATAAG) which is common among Arabian people. Family studies have shown that the two variations are located on opposite chromosomes. The hemolytic disease in this man, resembling Hb H disease, is likely the result of a severe downregulation of both alpha-globin genes on the chromosome with the alpha 2 poly A mutation, and the instability of the alpha-Taybe chain being the product of an alpha 1-globin gene; this leaves only one alpha 2-globin gene normally active.

The differences in quantities of alpha 2- and alpha 1-globin gene variants in heterozygotes.

We have identified through sequencing of amplified DNA the mutations in the alpha 2- and alpha 1-globin genes in 63 individuals with a heterozygosity for an alpha chain abnormal haemoglobin (Hb). Moreover, we developed a reverse transcription/polymerase chain reaction (RT/PCR) based procedure for the determination of the alpha 2- and alpha 1-mRNA ratio in normal individuals. The numbers of alpha 2 and alpha 1 variants were nearly the same. The average percentage of the abnormal Hb in heterozygotes with alpha 2 mutations (23.5%) was slightly higher than that in heterozygotes with alpha 1 mutations (19.7%) (stable Hbs only). These percentages correspond to a ratio of alpha 2 to alpha 1 of 1.19 to 1 at the protein level. Variations in the number of active alpha-globin genes and in the stability of the variants (greatly) affected the percentages of the abnormal protein. The average ratio between the alpha 2- and alpha 1-mRNAs in 12 normal individuals was 2.6-2.75 to 1, about as expected from published data, and 2.0 to 1 for two persons with an alpha-thalassaemia-2 (alpha-thal-2) (-3.7 kb) heterozygosity. The high relative mRNA (alpha 2) level which is about twice the relative level of the alpha 2 protein suggests a less efficient translation of the alpha 2-mRNA.

Hb Fannin-Lubbock in five Spanish families is characterized by two mutations: beta 111 GTC-->CTC (Val-->Leu) and beta 119 GGC-->GAC (Gly-->Asp).

We have sequenced the amplified beta-globin genes of five, apparently unrelated, Spanish adults with a fast-moving hemoglobin variant, and observed a GGC-->GAC mutation at codon 119 which identified the abnormality as Hb Fannin-Lubbock or alpha 2 beta (2)119(GH2)Gly-->Asp. In addition, we found a GTC-->CTC change at codon 111 which leads to a Val-->Leu replacement at this location. Protein analysis of the beta A and beta X chains from one of these individuals confirmed that both mutations are located on the same chromosome. It is hypothesized that some other known variants may carry an additional mutation in one of their exons, resulting in a silent amino acid substitution which may have an effect on some physicochemical property. In the case of Hb Fannin-Lubbock, it appears likely that the Val-->Leu replacement at beta 111, rather than the Gly-->Asp replacement of beta 119, is the cause of the instability of the variant. The Hb Fannin-Lubbock variant in these Spanish families had a normal oxygen affinity.

Beta-thalassemia alleles and unstable hemoglobin types among Russian pediatric patients.

A recently initiated collaboration between Russian and American institutions has resulted in the characterization of several known or new beta-thalassemia alleles and unstable hemoglobin types. Nine known beta-thalassemia alleles were present which have also been found in Mediterranean, East Asian, and Black populations; the possibility of independent mutations for some of the rare alleles should be considered. Hb Durham-N.C./Brescia with a codon 114 (CTG-->CCG; Leu-->Pro) change was present in six members of two families. This condition and two new variants have the characteristics of a dominant type of beta-thalassemia heterozygosity with moderate anemia, Heinz body formation, splenomegaly, etc. One new beta-thalassemia allele is a frame-shift at codon 124 (-A), while another is characterized by the introduction of an extra proline residue (codon: CCA) between residues Thr (beta 123) and Val (beta 126) to give the sequence -Thr-Pro-Pro-Pro-Val-.

Two different mutations in codon 68 are observed in Hb G-Philadelphia heterozygotes.

Through sequencing of amplified DNA containing the appropriate alpha-globin genes we have identified the base substitution leading to the formation of Hb G-Philadelphia [alpha 68(E17)Asn Lys]. Three subjects (approximately 25% Hb G) had an ACC AAA change at codon 68 of the alpha 2-globin gene; the chromosome with this mutation carried two alpha genes (alpha alpha). Six subjects (approximately 33% Hb G) had an AAC AAG change at the same codon of the alpha 2 alpha 1 hybrid gene on a chromosome with the 3.7 kb deletion (-alpha 3.7). These results indicate two independent mutations which likely occurred in different populations; increase in the level of Hb G is primarily dependent upon the loss of one or more alpha-globin genes.