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PubMed1989

[Analysis of phenotypic manifestations of abnormal human hemoglobins].

Phenotypic manifestations of abnormal human hemoglobins are discussed using the data of hematology, protein chemistry and molecular biology. On the basis of the presented analysis it is proposed to distinguish between phenotypic manifestations characterizing the primary molecular defect, i.e. properties of a mutant protein and their expression on the molecular and cellular levels; manifestations characterizing the equilibrium of the primary defect and compensatory potentialities of the organism; and finally the unbalanced state when the compensatory abilities of the organism are depleted. These different manifestations of the same defective gene reflect the most relevant peculiarities of mutant protein properties per se, expression of the properties in the living organism, the influence on the homeostatic system "mutant protein--organism" of the genetic and environmental factors both at the compensation state and at stress.

Hemoglobins, Abnormal↗
PubMed1981

The structure of hemoglobin Creteil (beta 89 Ser replaced by Asn) is similar to that of abnormal human hemoglobins having sequence changes at Tyr 145 beta.

In normal deoxyhemoglobin A, the beta chain COOH-terminal peptide adopts a well ordered structure which is needed for the full expression of allosteric action. Our crystallographic studies of deoxyhemoglobin Creteil (beta 89 Ser replaced by Asn), a variant hemoglobin characterized by high oxygen affinity and a very low level of allosteric function, show that replacement of Ser 89 beta by asparagine causes severe disordering of the beta chain COOH-terminal tetrapeptide. This results, as shown by our spectroscopic studies, in the destabilization of the quaternary structure of deoxyhemoglobin Creteil. We find, furthermore, that the changes in tertiary structure observed in deoxyhemoglobin Creteil are common to other variant hemoglobins having similar functional abnormalities but very different changes in primary structure. In particular, direct comparison of the difference electron density map of deoxyhemoglobin Creteil with that of deoxyhemoglobin Nancy (beta 145 Tyr replaced by Asp) suggests that these two abnormal hemoglobins may have the same mechanism of dysfunction despite the very different nature of their respective sequence changes.

Amino Acid Sequence↗
PubMed1999

[Globin gene mutation is a model of genetic abnormalities].

Hemoglobin has been extensively studied as a prototype of molecular abnormality, and abnormal hemoglobins have disclosed a number of molecular pathogeneses. Genetic analysis of hemoglobin has also contributed to recent advances in molecular biology. Here, thalassemia (thal) is examined. It is a congenital type of hemolytic anemia caused by defective production of either alpha- or beta-globin due to various genetic abnormalities and is referred to as alpha- or beta-thal, respectively. beta-thal is mainly caused by a point mutation, deletion or insertion of a few nucleotides resulting in decreased transcription, inability of initiating translation, abnormal RNA processing, frameshift, premature termination and production of super unstable hemoglobins. In many cases, the amount of mRNA carrying the mutation seems to be decreased. Reduced mRNA would prevent the subsequent formation of an abnormal translational product which is unstable and deleterious to the red cell membrane. Many alpha-thal's, in contrast, have an extensive gene deletion including the alpha-globin genes. Alu reiterative sequence plays an important role in the recombination of alpha-globin gene clusters which give rise to a large deletion or alpha-thal.

Alu Elements↗
PubMed1997

A new fast-moving variant causing erythrocytosis and mild hemolysis: Hb Gàmbara [beta 82(EF6)Lys-->Glu].

Hb Gàmbara is a new hemoglobin variant with abnormal beta chains that has been found in three out of four members of a family of Lombardy origin (Gàmbara, Brescia, Northern Italy). The affected subjects led a normal life, but they had modest erythrocytosis and mild (compensated) hemolysis with slight splenomegaly. Their abnormal hemoglobin was about 52% of the total hemoglobin, and was shown to be stable by the isopropanol test. Whole blood P50 of the proband was 19.3 Torr, Bohr effect was decreased (-0.25), as well as the molar ratio between the 2,3-diphosphoglycerate level and total hemoglobin of erythrocytes (0.68). The purified abnormal hemoglobin was characterized by an altered oxygen affinity, low n-factor, chloride, and 2,3-diphosphoglycerate effects. The Bohr effect was about 40% of the normal control. The abnormal hemoglobin moved faster than Hb A at alkaline electrophoresis, and split into two fractions, probably due to the formation of hybrid tetramers (alpha 2 beta A beta X). The reversed phase high performance liquid chromatogram from the tryptic digest of the aminoethylated abnormal beta chain subunits indicated the presence of an extra peptide, beta T-9, 10, replacing the individual peptides beta T-9 and beta T-10. Finally, the proband's DNA, drawn from a suitable segment of the beta structural gene (exon 2), revealed a nucleotide sequence carrying the heterozygous mutation AAG-->GAG at codon 82. This led to a Lys-->Glu substitution at position 82(EF6) of the beta chain.

Electrophoresis↗