A galactose-rich, cell-wall glycoprotein from styles of Nicotiana alata

A basic, galactose-rich style glycoprotein (GaRSGP) encoded by a previously characterized style-specific cDNA (NaPRP4) has been isolated from the styles of Nicotiana alata and structurally characterized. The glycoprotein is associated with cell walls in the transmitting tract and is composed of approximately 25% (w/w) protein and 75% (w/w) carbohydrate. The purified glycoprotein appears as a smear of between 45-120 kDa on SDS-PAGE; the deglycosylated protein backbone has an apparent molecular weight of approximately 30 kDa. The glycoprotein is rich in the amino acids lysine, proline, and hydroxyproline and in the monosaccharides galactose and arabinose. It is one of only a few proline/hydroxyproline-rich glycoproteins (P/HRGPs) to be characterized both as a cDNA-clone and protein. Glycans are attached to the protein backbone through both O- and N-glycosidic linkages with the majority of the carbohydrate being O-linked and consisting of short, highly branched chains terminating primarily in galactose residues. A carbohydrate epitope(s) is found on both GaRSGP and another style-specific glycoprotein but not on glycoproteins from other tissues. This finding provides further evidence for the existence of a style-specific carbohydrate epitope(s) which may play a role in style function.