Elements of secondary structure in a human epithelial mucin core peptide fragment.

The protein core of human epithelial mucin has previously been shown to consist of tandem repeats of a 20-amino-acid sequence that carries the epitopes for a number of tumour-marking monoclonal antibodies. High-field n.m.r. studies have now been undertaken on an 11-amino-acid fragment of this sequence dissolved in dimethyl sulphoxide. The studies reveal elements of secondary structure to be present: a type I beta-turn has been identified from Asp2 to Arg4 of this peptide, and this turn is extended by Pro5 being in the trans form. The observed turn region extends into the known epitopes for the antibodies C595 and NCRC-11 and may form the basis for how the antibodies recognize these peptides.