Characterization of phosphorylated oligomannosides from Hansenula wingei mannoprotein

Yeast cell wall mannoproteins often contain phosphate esterified to the oligosaccharide side chains, and partial acetolysis yields both neutral and phosphorylated fragments [Thieme, T. R., & Ballou, C. E. (1971) Biochemistry 10, 4121--4129]. We have isolated the acidic acetolysis fragments from Hansenula wingei mannoprotein [Yen, P. H., & Ballou, C. E. (1974) Biochemistry 13, 2420--2427] and have separated them into a mannopentaose monophosphate (Man5P) and a mannotriose monophosphate (Man3P). On the basis of selective enzymatic and partial acid hydrolysis and 1H and 31P NMR studies, Man5P was shown to have the structure P leads to 6 alpha Man1 leads to 3 alpha Man1 leads to 2 alpha Man1 leads to 2 alpha Man1 leads to 2Man (where Man = D-mannopyranose). The 31P NMR spectrum of the Man3P showed it to be a mixture of a phosphate monoester and a phosphate diester, which was separated by ion-exchange chromatography. The monoester had the structure P leads to 6 alpha Man1 leads to 3 alpha Man1 leads to 3Man whereas the diester had the properties of a cyclic phosphate. Although native H. wingei mannoprotein contains phosphodiester linkages, the starting mannoprotein preparation was isolated under alkaline conditions that hydrolyze such bonds, and it did not show a phosphodiester signal in the 31P NMR spectrum. We conclude that the cyclic phosphate was an artifact formed during the acetolysis reaction. Because acetolysis of H. wingei mannoprotein yields only phosphorylated mannotriose and mannopentaose whereas the mannoprotein contains mannotetraose side chains as well, the phosphorylation process must be a very specific event in the biosynthesis of the glycoprotein.