Overexpression and characterization of two human salivary proline rich proteins

Proline rich proteins (PRP) are among major human saliva constituents and are known to interact with wine tannins that are involved in astringency. To characterize these interactions, a human salivary proline rich pro-protein, PRB4S, was overexpressed in Pichia pastoris. Six recombinant proteins resulting from maturation in bioreactor were detected by SDS-PAGE analysis between 15 and 45 kDa (apparent molecular weight). Two of them, the 45 and the 15 kDa ones, were isolated from culture supernatant by adsorption and permeation chromatography. They were characterized by N-terminal sequencing and MALDI-TOF analysis after trypsic digestion. The 45 kDa protein is glycosylated while the 15 kDa one was obtained after a furin-like proteolysis. Both of them are similar to human whole saliva PRP resulting from proteolysis of PRB4S pro-protein in Golgi network and known as II-1 and IB-5. Because of their sensitivity to proteolysis or their unusual mobility on SDS-PAGE gel, these recombinant proteins seem to be intrinsically unstructured proteins.