Our primary goal is the development of useful synthetic glycopeptide mimics that effectively represent cell surface O-glycopeptides initiated as alpha-linked: O-GalNAc and O-Man Ser/Thr. These mimics will provide metabolic stability to enhance bioavailability, and are expected to have altered binding affinities to immune surveillance molecules to help break inherent immunotolerance in the O-GalNAc case. O-Mucins represent a family of transmembrane glycoproteins important for the elaborate cell surface glycan display. Carcinogenesis has a deleterious effect on these extracellular glycoforms leaving truncated structures known as tumor-associated carbohydrate antigens. The shortest of these is the core residue monosaccharide, GalNAc alpha-linked to the hydroxyl of Ser/Thr, known as Tn antigen. The expression of Tn antigen alters phenotypic properties such as adhesion, migration, and metastasis, and so has potential as a biomarker for diagnostic and prognostic purposes, as an antigen for vaccine development, and for use in the development of anti-Tn mAbs to target drug delivery. An improved understanding of structure-function relationships of Tn antigen in the context of the mucin, MUC1, will help guide rational design for translational research. O-Glycopeptide structural studies, specifically related to Tn antigen, have pointed to intramolecular interactions between the GalNAc and the peptide backbone via H-bonding. Although molecular mimics to Tn antigen have been the target of numerous synthetic and immunological studies, many have not considered the established conformational preferences. Initiatives for the development of improved mimetic design are proposed here. Specifically a metabolically robust C-linkage is designed, yet one with a pendant hydroxyl to maintain the key H-bonding network to properly orient the glycan with respect to the peptide. We herein propose to synthesize pure, robust mimics of Tn antigen, with conformational realism, as they may be presented from the backbone of biomedically relevant peptides (such as MUC1) and to compare these mimics with Tn antigen itself, by NMR and molecular dynamics simulations for clarification of the essential structural features necessary to maximize biological activity. The most promising mimics will be incorporated into MUC1 peptide sequences for immunological and tumor inhibition studies by collaborators.
Beyond these typical O-mucins, there exist glycosylated mucin-like domains on alpha-dystroglycan (alpha-DG) that are critical for cell adhesion to the extracellular matrix. Hypoglycosylation of alpha-DG has been implicated in a variety of congenital muscular dystrophies and tumor cell metastasis. These structures are O-mannosyl-apha-Ser/Thr initiated. In addition, a growing number of related O-mannosyl proteins have recently been discovered, and their biological roles are as yet undetermined. One means of identifying such structures is through the use of mannose-specific antibodies, which are limited in number. Herein, we propose to prepare a stable C-linked Man-alpha-Ser for incorporation into relevant peptide sequences as an antigen for antibody induction.