Deletion of amino acid residues 33-46 in growth hormone alters the hydrophobicity of the molecule

Growth hormone (GH) variants have been studied for the structure-function relationship of the molecule. The presence of a potential alternate splicing point in mRNA in bGH gene at exon 3, similar to hGH has been reported by workers. Early investigation on the characteristics of the chemistry of 20k oGH showed that the molecule was produced by site-directed mutagenesis by deleting amino acid residues 33-46 and the resultant DNA was expressed in E. coli under the control of lac promoter in pUC based plasmid. The mutant protein remained insoluble and did not refold. To investigate the effect of deletion on the chemistry of the molecule, computational biology tools were employed. The mutant with the deletion of amino acid residues 33-46, was designed and the model was visualized on computer. The structure of 20k bGH was compared with bGH and dissected for hydrogen bonds and hydrophobicity. Computational biology tools were helpful in elucidating the role of 33-46 amino acid residues domain in the chemistry of the molecule. Furthermore, it was revealed that removal of amino acid residues 33-46 which formed the hydrogen bonds involving Glu 33, Gln 46, Pro 38, Arg 42, Tyr 43,Ala 51, Thr 48, Asn 47, led to the formation of new hydrogen bonds between Thr 33, Tyr 144, Asn 32, Asn 32 and Ser and Asp 153. The removal of the amino acids 33-46 decreased the hydro-phobicity of the first helix of bGH molecule, as compared to 20k hGH, thus altering the solubility of the molecule, confirming the earlier reported results for ovine growth hormone with same deletion.