Augmentation of structural stability in model peptide systems through redesign and post-translational modification

Investigation of the driving forces that dictate protein folding, molecular recognition and biomolecular interactions is paramount for our understanding of complex biological processes. Post-translational modifications of proteins are a key component of cell signaling. Such modifications on the N-terminal tails of histone proteins are known to regulate gene transcription in eukaryotic organisms. Two modifications of particular interest to histone proteins are methylation of lysine and phosphorylation of serine, both which are known to modulate gene transcription. To determine how these modifications affect beta-sheet structure, they were investigated in model beta-hairpin systems. Small beta-hairpin systems allows for the description and quantification of specific interactions which leads to a deeper understanding of the driving forces involved in complex biological processes.;Phosphorylated amino acids were incorporated into a designed beta-hairpin peptide to study the effect on beta-hairpin structure when the phosphate group is positioned to interact with a tryptophan residue on a neighboring strand. It is shown that phosporylation destabilizes the hairpin structure. The incorporation of two tryptophan residues to form an aromatic pocket that interacts with a lysine or N-methylated lysine was investigated in a beta-hairpin peptide system. This tryptophan pocket results in an enhancement in the stability of the beta-hairpin. Using a combination of phosphorylation and methylation, we were able to design a beta-hairpin peptide in which the stability can be controlled through incorporation of the different posttranslational modifications. Incorporation of dimethylated lysine results in an increase in hairpin stability, while phosphorylation of serine completely unfolds the hairpin.;A naturally occurring beta-hairpin in Ubiquitin was also redesigned to investigate how alternative interactions affect the fold of a natural system. These studies indicate that deletion of Met1 and Val17 from results in a destabilization in hairpin structure by 0.7 kcal/mol.;Initial studies were conducted to determine the necessary requirements to promote favorable tertiary contacts between a beta-hairpin alpha-helix and an for future designed systems. Peptides based on fragments of the GB1 protein that form an alpha-helix and a beta-hairpin in the native protein were modified to promote their prospective secondary structure and were subsequently investigated. However, the experiments conducted yielded ambiguous results.