Circular dichroism studies on the proline-rich glycoprotein of human parotid saliva

Previous results on the primary structure of the human parotid saliva proline-rich glycoprotein established the concept of repetitive domains in the sequence of that glycoprotein, tryptic glycopeptides of proline-rich glycoprotein representing the basic structure. The present work is concerned with the study of the secondary structure of the proline-rich glycoprotein, and of tryptic glycopeptides with and without the glycan moiety, using circular dichroism. CD spectra exhibit the same secondary structure with about 60% of polyproline II helical structure for the proline-rich glycoprotein, tryptic glycopeptides and their deglycosylated homologues. The present results are in fair agreement with the amino acid sequence results and suggest a model for the schematic representation of the proline-rich glycoprotein.