Glycosylation as a Structural Determinant in Peptide Fibrillization

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Project Summary. All human cell surfaces and nearly half of all human proteins are decorated with carbohydrates (i.e., glycosylated), yet our understanding of the role of glycosylation in health and disease remains limited. Increasing evidence is establishing a central role for glycosylation as a determinant of protein folding, sorting, processing, export, and function. Advancing this understanding requires platforms to systematically study changes in protein form and function resulting from altered glycosylation, which has historically required highly specialized expertise in protein production and carbohydrate synthesis. As a practical alternative, my research program develops carbohydrate-modified peptides that self-assemble into fibrillar architectures as synthetic analogs of glycosylated proteins. The proposed research program will study how glycosylation influences peptide fibrillization as a surrogate for protein folding, and will use these insights to enable design of new biomaterials. Preliminary data supporting the proposed research demonstrate that glycosylation can facilitate hierarchical self-assembly of a synthetic b-sheet fibrillizing peptide into anisotropic networks of aligned nanofibers. These anisotropic networks resist non-specific biological interactions yet selectively recognize carbohydrate-binding proteins due to the emergent function of carbohydrates assembled into a multivalent architecture. The overarching hypothesis of the proposed research is that glycosylation influences peptide fibrillization and nanofiber function by establishing intermolecular forces that mediate specific binding interactions while preventing non-specific associations. To test this, we will first develop a method for scalable, cost-effective synthesis of a library of fibrillizing peptides modified with a broad range of carbohydrate chemistries. Then we will use this library to study the influence of glycosylation on the kinetics of peptide fibrillization and equilibrium morphology of the resultant nanofibers using various biophysical methods. Together, these studies will establish fundamental understanding of glycosylation as a structural determinant in peptide fibrillization. Finally, we will evaluate glycosylated peptide nanofibers as biomaterials that recapitulate the form and function of lubricin, a cartilage glycoprotein that provides boundary lubrication at the joint surface, which is lost during osteoarthritis progression. Although we use synthetic fibrillizing peptides as a model system, general observations made through this research program are expected to be applicable to the biophysics of natural fibrillizing peptides, and may also inform understanding of mucins and other densely glycosylated proteins. Success of this research will advance the field of supramolecular biomaterials by establishing carbohydrates as a new class of molecular motif for controlling peptide fibrillization. Ultimately, this research will support future efforts to develop biomaterials with new structural and functional properties that are desirable for biomedical applications by creating peptides modified with diverse carbohydrate chemistries found throughout nature.