Hemoglobin globin chains

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Hemoglobin is a tetramer built up of two copies each of two different polypeptide chains, a- and (5-globin chains in normal adults. Each of the four chains has the globin fold with a heme pocket. Residue 6 in the p chain is on the surface of a helix A, and it is also on the surface of the tetrameric molecule (Figure 3.13). 

Figure 89 illustrates two different tries at simplified representation of the globin structure. For reference, Fig. 89a shows the hemoglobin /3 chain in stereo. Figure 89b shows the globin structure schematically as two layers of helices with the elements in one layer approximately perpendicular to those in the other layer this can be contrasted with a possible description of the up-and-down helix bundles as two layers with their elements approximately parallel to each other. The perpendicular layers provide a rather successful simple schema for the globin structure, but unfortunately there are no other proteins that can be adequately described as two perpendicular layers of helices. Also, specification of the topology in this scheme is cumbersome, since the chain skips back and forth between layers. 

Sickle hemoglobin (HbS) differs from normal adult hemoglobin (HbA) at amino acid number 6 of the P-globin chain, where HbS has a Val and HbA a Glu. 

Basis of the Sickle-Cell Mutation Sickle-cell hemoglobin has a Val residue at position 6 of the j3-globin chain, instead of the Glu residue found in normal hemoglobin A. Can you predict what change took place in the DNA codon for glutamate to account for replacement of the Glu residue by Val ... 

Abnormal hemoglobulins can be detected by electrophoresis, as shown in Figure 7.4, which includes a pattern observed in /3+-thalassemia and one in a newborn with a-thalassemia (possibly HbH disease). It should also be mentioned that, unless there is a coexisting hemoglobin abnormality resulting from a point mutation or crossover problem, the globin chains of classic a- and /3-thalassemia are perfectly normal. It is usually the quantities of either the a or the /3 chains that are decreased. Some frameshifts have been found near the terminus of the /3 chain that lead to frameshift mutations in certain areas. 

Hemoglobin ((3-globin chain) Oxidation of Meth-p55D6 Increase in in affinity to oxygen abolition of Bohr effect (A10)... 

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