Conformational study of the basic proline-rich polypeptides from human parotid saliva.

The conformational study of two basic proline-rich polypeptides from human parotid saliva, P--D and P--E of known primary structures, was performed by CD and 1H--n.m.r. spectra measurements. These polypeptides contain consecutive sequences of five prolyl residues in their amino acid sequences. The troughs in CD spectra of P--D and P--E were found at 202 and 201 nm, respectively. These wavelengths were different from the value of 206 nm of poly-L-proline form II conformation. In spite of this, the existence of poly-L-proline form II conformation was suggested in the structure of P--D, because the trough for a fragmental peptide of P--D containing five consecutive prolyl residues was found at 204 nm. No remarkable change was detected in CD and 1H--n.m.r. spectra of P--D and P--E in the range of pH 3.0-11.0. The result suggests that no folding of polypeptide which might be affected by ionic interaction exists in its structure.