Structure-Function Relation of Somatotropin with Reference to Molecular Modeling

Amtul      Jamil Sami

Abstract

Somatotropin, commonly known as growth hormone (GH) is a polypeptide chain containing about 190 amino acid residues, produced by the pituitary gland in mammals and is responsible for a number of anabolic processes. It has two disulphide bridges, with 4 alpha helices arranged in anti-paralel distinctive manner. GH molecule binds with two receptor molecules to exhibit its full biological activity. In this review, the information regarding charecterization, structure and function is updated. A number of human growth hormone variants (naturally occuring and poduced by recombinant DNA- technology) are visualised, and structure related functions are revealed. 1) The di-sulphide bridges are not essential for the biological activity of the molecule. The two chain variants of GH are able to show full biological activity. 2) The different domains of GH could be related to its functions 3) N-terminus of the molecule is involved in the galactopoietic activity of the molecule. 4) A single amio acid residue at a particular position could determine the magnitude of hormone receptor binding. 5) Role of Trp 86 is critical in packing of the apha helices bundles of the molecule. 6) Hydrophobic cores are essential for the stability of GH molecule 7) Salt bridges and hydrogen bonds are also important for the binding of the molecule with its receptors. 8) GH molecule has two binding sites for receptor molecules, SiteI and Site II which are sterically coupled. The placental growth hormone has also been discussed and compared with the pituitary derived GH for its structure and function.

Keywords: disulphide bridges, hGH variants, Trp 86 deletion, placental growth hormone, mutation

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