| MUC1 mucin is a transmembrane glycoprotein composed of repeating units of a 20 amino acid sequence (VTSAPDTRPAPGSTAPPAHG), expressed on the apical surface of epithelial cells. Formation of the MUC1 tumor antigen occurs due to upregulation of protein expression and a dramatic decrease in glycosylation, which leads to exposure of normally hidden carbohydrates and the peptide core. While there have been attempts to create an effective vaccine using either unglycosylated peptide or a sugar based systems, none have been successful at removing a tumor, since they do not truly represent the cancerous state. Antibody B27.29, which was raised against breast tumor cells, and should therefore bind most tightly to the molecule that most closely resembles the tumor state was used as a reverse-template to determine the tumor-associated state and the best vaccine candidate. Using Nuclear Magnetic Resonance Spectroscopy, it has been determined that antibody B27.29 recognizes a short sequence (PDTRPAPG), which contains a type I β-turn (in bold). The details of this interaction and the effect of increasing repeat on the structure, dynamics, and affinity to antibody are discussed in the context of vaccine design. Additionally, the effect of glycosylation within the β-turn B-cell epitope on structure, dynamics, and interaction with antibody B27.29 has been studied. These studies provide key insights into the composition of a second generation MUC1 breast cancer vaccine. |
