Induction of protein-like molecular architecture by monoalkyl hydrocarbon chains.

Numerous approaches have been described for creating relatively small folded biomolecular structures. "Peptide-amphiphiles," whereby monoalkyl or dialkyl hydrocarbon chains are covalently linked to peptide sequences, have been shown previously to form specific molecular architecture of enhanced stability. The present study has examined the use of monoalkyl hydrocarbon chains as a more general method for inducing protein-like structures. Peptide and peptide-amphiphiles have been characterized by CD and one- and two-dimensional nmr spectroscopic techniques. We have examined two structural elements: alpha-helices and collagen-like triple helices. The alpha-helical propensity of a 16-residue peptide either unmodified or acylated with a C(6) or C(16) monoalkyl hydrocarbon chain has been examined initially. The 16-residue peptide alone does not form a distinct structure in solution, whereas the 16-residue peptide adopts predominantly an alpha-helical structure in solution when a C(6) or C(16) monoalkyl hydrocarbon chain is N-terminally acylated. The thermal stability of the alpha-helix is greater upon addition of the C(16) compared with the C(6) chain, which correlates to the extent of aggregation induced by the respective hydrocarbon chains. Very similar results are seen using a 39-residue triple-helical model peptide, in that structural thermal stability (a) is increasingly enhanced as alkyl chain length is increased and (b) correlates to the extent of peptide-amphiphile aggregation. Overall, structures as diverse as alpha-helices, triple helices, and turns/loops have been shown to be induced and/or stabilized by alkyl chains. Increasing alkyl chain length enhances stability of the structural element and induces aggregates of defined sizes. Hydrocarbon chains may be useful as general tools for protein-like structure initiation and stabilization as well as biomaterial modification.

Protein-like molecular architecture: biomaterial applications for inducing cellular receptor binding and signal transduction.

The development of biomaterials with desirable biocompatibility has presented a difficult challenge for tissue engineering researchers. First and foremost, materials themselves tend to be hydrophobic and/or thrombogenic in nature, and face compatibility problems upon implantation. To mediate this problem, researchers have attempted to graft protein fragments onto biomaterial surfaces to promote endothelial cell attachment and minimize thrombosis. We envisioned a novel approach, based on the capability of biomolecules to self-assemble into well-defined and intricate structures, for creating biomimetic biomaterials that promote cell adhesion and proliferation. One of the most intriguing self-assembly processes is the folding of peptide chains into native protein structures. We have developed a method for building protein-like structural motifs that incorporate sequences of biological interest. A lipophilic moiety is attached onto a N alpha-amino group of peptide chain, resulting in a "peptide-amphiphile." The alignment of amphiphilic compounds at the lipid-solvent interface is used to facilitate peptide alignment and structure initiation and propagation, while the lipophilic region absorbs to hydrophobic surfaces. Peptide-amphiphiles containing potentially triple-helical or alpha-helical structural motifs have been synthesized. The resultant head group structures have been characterized by CD spectroscopy and found to be thermally stable over physiological temperature ranges. Triple-helical peptide-amphiphiles have been applied to studies of surface modification and cell receptor binding. Cell adhesion and spreading was promoted by triple-helical peptide-amphiphiles. Cellular interaction with the type IV collagen sequence alpha 1(IV) 1263-1277 increased signal transduction, with both the time and level of induction dependent upon triple-helical conformation. Collectively, these results suggest that peptide-amphiphiles may be used to form stable molecular structure on biomaterial surfaces that promote cellular activities and improve biocompatibility.