Hemoglobin beta subunits

Unzai S et al Rate constants for O2 and CO binding to the alpha and beta subunits within the R and T states of human hemoglobin. J Biol Chem 1998 273 23150. 

Normal hemoglobin molecules are complex, three-dimensional structures consisting of four chains of amino acids known as polypeptide chains. Two of these chains are known as alpha subunits with 141 amino acid residues each, and the remaining polypeptide chains are the beta subunits with 146 amino acid residues each. The sequences of amino acids in the alpha and beta subunits are different, but fold up via noncovalent interactions to form similar three-dimensional structures. When a polypeptide chain arranges itself in space, i.e., when it folds, amino acids that were far apart in the chain are brought closer in proximity. The final overall shape of the protein molecule is influenced by (1) the amino acids in the chain, and (2) the interactions that are possible between distant amino acids. 

In sickle cell hemoglobin, the glutamic acid of the beta subunit is replaced by the amino acid valine (Fig. 7.11.2). Even though only this one amino acid is... 

Luchsinger BP, Rich EN, Gow AJ, Williams EM, Stamler JS, Singel DJ. Routes to S-nitroso-hemoglobin formation with heme redox and preferential reactivity in the beta subunits. Proc. Natl. Acad. Sci. U. S. A. 2003 100 461-466. 

Hemoglobin (Hb) is a tetrameric protein composed of two identical alpha subunits and two identical beta subunits. X-ray crystal structures of the low (18) and high (20) affinity states of this protein have been solved at high resolution. 

Three components were found for the hemoglobin (6 Trp residues) and the tetrameric beta subunits (8 Trp residues), while the alpha chain (one Trp residue), its fluorescence decays with two components. What we may conclude from these results ... 

The tetramerie beta subunit does not present any T-R eonformational ehange, however the fluoreseenee deeay is three exponentials as for the human hemoglobin. 

Mathews. A.J. Olson. J.S. Assignment of rate constants for O2 and CO binding to alpha and beta subunits within R-and T-state human hemoglobin. Methods Enzymol. 1994, 232. 363-386. 

Davydov R, Kofman V, Nocek JM, Noble RW, Hui H, Hoffman BM (2004) Conformational substates of the oxyheme centers in alpha and beta subunits of hemoglobin as disclosed by EPR and ENDOR studies of cryoreduced protein. Biochemistry 43 6330-6338... 

The genetic defects known as thalassemias result from the partial or total absence of one or more a or P chains of hemoglobin. Over 750 different mutations have been identified, but only three are common. Either the a chain (alpha thalassemias) or P chain (beta thalassemias) can be affected. A superscript indicates whether a subunit is completely absent (a or p ) or whether its synthesis is reduced (a or P ). Apart from marrow transplantation, treatment is symptomatic. 

Figure 4.13 Anatomy of selected proteins. (A) The /3 subunit of hemoglobin carrying a heme molecule (B) triose isomerase and (C) /3-lactoglobulin carrying a molecule of vitamin A. Spirals represent helix segments, and the broad arrows are pleated sheet polypeptide segments showing the direction from the N to the C terminus. (A and B reproduced with permission from Richardson JS. The anatomy and taxonomy of protein structure. Adv Prot Chem 34 168-339, 1981. C reproduced with permission from Papiz MZ, Sawyer L, Eliopoulos EE, North ACT, Findlay JBC, Sivaprasadarao R, Jones TA, Newcomer ME, Kraulis PJ. The structure of beta-lactoglobulin and its similarity to plasma retinol-binding protein. Nature 324 383-385, 1986.)...

Connolly, M. L. (1986). Shape complementarity at the hemoglobin alpha 1 beta 1 subunit interface. Biopolymers 25(7), 1229-1247. 

M. L. Connolly, Biopolymers, 25, 1229-1247 (1986). Shape Complementarity at the Hemoglobin alpha 1 beta 1 Subunit Interface. 

---