Scanning tunneling microscopy imaging of the tumour associated antigenic 20 amino acid human polymorphic epithelial mucin core peptide fragment.

Human polymorphic epithelial mucins (PEM) are high molecular weight glycoproteins that are associated with breast cancer. Recent structural studies have identified that the protein core of PEM contains a 20 amino acid tandem repeat that has elements of secondary structure which coincide with the epitopes for a number of tumour reactive antibodies. In our continuing structural studies we have now investigated the use of the scanning tunneling microscope (STM) to directly image the conformation of the twenty amino acid PEM core peptide. High resolution STM images reveal that the peptide has an overall topography similar to that predicted by molecular modelling. The images identify directly that the free peptide is conformationally non-restricted and can adopt a number of discrete conformations in the solid state.