Interactions of supramolecular nanostructures with biological systems for advanced medical therapies

This dissertation examines the interface and interactions between self-assembling peptide amphiphiles (PAs) and biological systems. A fundamental study of biological recognition and accessibility was investigated by placing enzymatic recognition sites radially along the nanofiber. Enzymes were immobilized on agarose beads (∼20 mum) with short polyacrylamide linkers, modeling the membrane-bound receptors of a cell interacting with the PA. The measured rates of product formation from the enzymatic reaction correlated to accessibility and recognition of the substrate. It was discovered that while assembly into nanofibers decreases the rate of the reaction, the reaction occurs everywhere, even sites in the core of the nanofiber. For the first time, the accessibility of biomacromolecules into the core of the nanofiber has been confirmed and also changes the model of the assembled structure. A rigid, dense nanostructure cannot allow macromolecular access and therefore the nanostructure must be flexible, with the monomers able to bend, creating access for the enzyme. Upon successful formation of the enzyme-substrate complex, water bound to the surface of the PA monomer is released allowing for an entropically favorable reaction. Applications of nucleicacid and protein-binding PA nanofibers to deliver these molecules to elicit changes cellular biology were also studied. The protein activin A successfully bound to the PA but delivery was inefficient. The interface between the PA and a protein was discovered for the first time with hydrogen-deuterium exchange analysis; it was found that the PA was interfering with proteinbinding to the receptor. Once these unfavorable interactions were removed, the biological activity was restored. PA nanofibers were designed to bind to DNA and to actively transport the complex to the nucleus through nuclear localization signals. It was found that these complexes were more effective than commercially available complexes. The shape of the nanostructure also influences interactions with biological systems. Photo-cleavable nitrobenzaldehyde placed within the beta-strand forming region of the PA prevented association into nanofibers through molecular strain, instead producing nanospheres. Releasing the strain with UV irradiation allowed nanofiber formation. The resulting nanofibers were significantly more active in the formation of focal adhesions than the nanospheres, affording a system of light-triggered bioactivity.