Preparation, characterization and molecular modeling of PEGylated human growth hormone with agonist activity

In this study, site-specific PEGylated human growth hormone (hGH) was prepared by microbial transglutaminase, modeled and characterized. To this end, the effects of different reaction parameters including reaction media, PEG:protein ratios, reaction time and pH value were investigated. PEG-hGH was purified by size exclusion chromatography method and analyzed by SDS-PAGE, BCA, peptide mapping, ESI and MALDI-TOF-TOF mass spectroscopy methods. Biophysical and biological properties of PEG-hGH were evaluated. Molecular simulation was utilized to provide molecular insight into the protein-receptor interaction. The optimum conditions that were obtained for PEGylation were phosphate buffer with pH of 7.4, 48 h of stirring and PEG:protein ratio of 40:1. By this method, mono-PEG-hGH with high reaction yield was obtained and PEGylation site was at Gln-40 residue. The circular dichroism and fluorescence spectrum indicated that PEGylation did not change the secondary structure while tertiary structure was altered. Upon enzymatic PEGylation, agonistic activity of hGH was preserved; however, Somavert®, which is prepared by chemical PEGylation, is an antagonist form of protein. These data were confirmed by the total energy of affinity obtained by computational protein-receptor interaction. In conclusion, PEGylation of hGH was led to prepare a novel form of hormone with an agonist activity which merits further investigations.