Peptides as model systems, antimicrobial agents, and a means for protein superassembly.

Proteins are the most diverse class of biomolecules, both structurally and functionally, and have evolved to accomplish many tasks in living systems. The features of proteins and peptides that contribute to their structure, stability and activity have been elucidated through an enormous body of experimental work. Central to this research have been protein engineering and design studies. Knowledge of the basic principles underlying protein folding, stability, and activity provide insight into the fundamental processes in vivo and offer the potential of designing protein/peptide based materials and therapeutic agents. The extensive research on protein design and incorporation of non-natural amino acids into peptides and proteins forms the basis of the research presented. A de novo designed 4-alpha-helix bundle was employed to study the increased stability and potential self-segregating properties imparted by incorporation of the highly fluorinated amino acid, L-5,5,5,5',5',5'-hexafluoroleucine (hFLeu). The fluorinated peptide was shown to have increased biological stability against proteolytic degradation and greater stability toward denaturation by organic solvents in comparison to the non-fluorous peptide. Contrary to the predictions of the "fluorous" effect the fluorinated and non-fluorous peptides showed no tendency to self-segregate. A series of antimicrobial peptides were studied to examine the affects of fluorination on the stability and antimicrobial activity of the alpha-helical MSI-78 peptide and beta-hairpin PG-1 peptide. The fluorinated alpha-helical analogs of MSI-78 exhibited broad spectrum antibacterial activity, and importantly increased stability against proteolysis. However, hFLeu did not improve the antimicrobial activity of the beta-hairpin PG-1 antimicrobial peptide that was also investigated. The results suggest fluorination may improve the efficacy of AMPs. Finally, a alpha-helical coiled-coil peptide was investigated as a means of mediating higher order assembly of the 5-fold symmetric cholera toxin B protein (CTXB). When the alpha-helical peptide was genetically fused to the N-terminus of CTXB the fusion protein self-assembled into higher order assemblies of CTXB through dimerization of the N-terminal alpha-helical peptide domain. Further development of the system could be useful for the development of protein-based biomaterials.