Chemical synthesis of proteins containing post‐translational modifications and PNA‐templated disulfide bond formation
Date of Issue2012
School of Biological Sciences
The study of protein structure and function is a central topic of bioscience research. As the most important molecules of life, proteins often undergo post-translational modifications (PTM) in order to carry out their biological functions. A good example is the histone proteins whose PTMs include acetylation, methylation and ubiquitination on specific amino acid side chains. The understanding of how a protein exerts its function in either its native or post-translationally modified form can not only solve many problems in basic biology but also produce therapeutic breakthroughs in medicine. Protein chemical synthesis is a useful approach for the production of these modified proteins which are invaluable reagents for the structural and functional characterization of individual PTM events. In my study, two popular chemical ligation methods were studied for ligation at valine residue: the thioester-mediated ligation and thioacid capture ligation. An N-terminal penicillamine was used to mediate the ligation reaction, similar to the Cys-mediated chemical ligation. Subsequent desulfurization gives a Val residue at the ligation site. However, the steric hindrance of the tertiary thiol group in penicillamine significantly slows down the ligation reaction as compared to ligation at a cysteine residue. Several model peptide thioesters and thioacids were prepared to ligate with the penicillyl peptides by the respective ligation methods. From the results, we can conclude that the thioacid capture ligation works very well for ligation at the sterically hindered Pen compared with the thioester-mediated ligation. A modified histone H2B K120Ac was successfully synthesized by the thioacid capture ligation method. Moreover, a new strategy was developed for the purification of the ligation product.