Synthesis of a MUC1 Mucin Cyclic Dimer Peptide and Its Antibody Binding Properties as Revealed by STD-NMR

In a previous study we showed that the shortened MUC1 mucin peptide GVTSAPD could bind monoclonal antibody (mAb). We proceeded on to make a cyclic peptide of the same sequence to see if it would be more effective in binding antibody. We were able to synthesize and isolate two different cyclic mucin peptides: 1) a monomer cyclic peptide with sequence GVTSAPD which we did not study due to difficulties in achieving homogeneity, and 2) a dimer cyclic peptide with sequence GVTSAPDGVTSAPD that was successfully isolated and studied. We describe here the results of the dimer cyclic peptide-antibody interactions obtained by Saturation Transfer Difference NMR (STDNMR). The results indicated that the protons of all residues experienced STD effects, notably being more pronounced at Pro, Val, Ala and Asp compared to the linear peptide GVTSAPD. The Pro residue exhibited STD peaks for all its side chain protons with stronger intensity at ProHγ while Ala, Val and Thr are localized to methyl groups.