Synthesis and testing of novel polypeptides for biological applications

Abstract

Natural systems produce macromolecules that assemble into complex, highly ordered structures. In particular, proteins and peptides derived from the 20 naturally occurring amino acids are sequenced macromolecules that can fold into secondary and tertiary structures and can self assemble into quaternary structures. Through weak interactions, these ordered systems produce high-strength materials, provide physical cues to induce cell functions and morphologies, efficiently harvest energy, and transport materials. One of the key challenges in the field of polymer chemistry is the ability to generate synthetic systems that can demonstrate the highly ordered structure, self-assembly, and responsive behavior of these macromolecules. Synthetic polypeptides have received attention because of their unique structural properties and biocompatibility. Like their naturally occurring analogs, these molecules have a poly(amino acid) backbone and posses the ability to fold into secondary structures. Synthetic homo polypeptides are synthesized by the ring opening polymerization of N-carboxyanhydrides formed from naturally occurring amino acids. Although these macromolecules' secondary structure can be controlled to some extent, we are limited by the given side chain, which dictates polymer function, structure, and responsive behavior to temperature or pH among many other properties. We have developed a new approach to the manipulation of synthetic polypeptide composition and function through the introduction of a new NCA polymer, poly(Y-propargyl-L-glutamate) (PPLG) which contains a pendant alkyne group that can be reacted with an azide by the 1,3 cycloaddition "click" reaction. With this system, we can incorporate functional groups that are ordinarily difficult to introduce because of cross-reactions or exhaustive protection-deprotection steps. In addition, we can more directly mimic the adaptive function and responsive behavior of naturally occurring polypeptides. This thesis focuses on the development of the PPLG system and the use of the system for synthetic biomimics, drug delivery, and gene delivery. For synthetic biomimics, as an initial example, densely grafted polymers were synthesized to demonstrate the utility of this synthetic approach. In addition, synthetic antimicrobial polypeptides were synthesized to mimic naturally occurring antimicrobial peptides. For drug and gene delivery, a library of pH responsive peptides were synthesized and characterized.