Towards Bio-inspired and Functionalized Peptide Materials

Abstract

Peptide-based materials constitute a class of molecules that play an important role in many biological processes and are utilized by many organisms to interact with their environment. One of the most well-known examples is spider silk, a material produced by web-spinning spiders composed of repeating stretches of amino acids that has a very high tensile strength. Many peptide-based materials are composed of repeating stretches of certain amino acids that confer function and (macroscopic) structure to these materials. In the first three research chapters a peptide material based on naturally occurring antifreeze molecules from arctic fish is described. In nature this material is composed of repeating stretches of a glycosylated tripeptide. Our mimic is synthesized by a copper-catalyzed polymerization reaction from a modified glycotripeptide with polymerization handles. This polymerization reaction introduces a non-natural element in the peptide backbone that was known to mimic the natural amide bond in previously published examples to a certain extent. A one-pot reduction and polymerization yielded a mixture of oligomers that could be separated by size. Upon analysis of the antifreeze activity of the resulting antifreeze mimics by an ice recrystallization experiment, the polymeric material was shown to have a strongly reduced antifreeze activity compared to the natural compound and a synthetic derivative synthesized previously. Structural analysis by circular dichroism showed a similar structure to the previously described and potent synthetic antifreeze glycopeptide, indicating that a small structural change can abolish the potent antifreeze properties of such molecules. The chemistry for introducing a urea moiety that can be incorporated into the antifreeze glycopeptides to enhance the interaction with the ice-lattice is described, using a 4-chlorophenyl glycoside synthon that can react with amines under mild conditions to form a ureido glycoside linkage. As a case study, this chemistry was used to synthesize a urea-containing glycopolymer based on the previously synthesized mimic. In chapter five a modification of the naturally occurring antibiotic nisin is described, wherein commercially available nisin was conjugated on the C-terminus with propargylamine, a handle for copper catalyzed click chemistry. In a second step this modified nisin could be coupled to fluorescent reporter molecules, and as a proof-of-concept, a small molecule with two azide handles. The successful synthesis of the dimeric nisin structure and retention of antimicrobial activity of all conjugates indicated the possibility to easily incorporate nisin in a functionalized (peptide) material or surface to obtain antimicrobial peptide based materials. In chapter six a dicysteine motif is described, which easily oxidizes to a cyclocystine. Initially found in a peptide derived from Tamm-Horsfall protein (F991) that was indicated to bind free-light chains, it became apparent that in serum this peptide rapidly formed the cyclocystine moiety. Attempts to use this structural motif in the beta-sheet forming human islet amyloid polypeptide as an oxidative switch are described. Preliminary results show a distorted structure by circular dichroism, but the resulting peptide still formed similar structures in aqueous buffer. Further attempts at increasing the change upon oxidation are described.