Structure of Glucomannan-Protein from the Yeast Cryptococcus Laurentii

Abstract

The structure of an extracellular glucomannan-protein produced by Cryptococcus laurentii was studied. The glucomannan-protein was isolated via its insoluble copper complex. It was homogeneous on free-boundary electrophoresis, contained 91% saccharide, 6.5% protein and 1% phosphorus. It had M_n 21,000. The carbohydrate portion was composed of D-mannose and D-glucose in 33:2 molar ratio. From the results of compositional and methylation analyses, conventional acetolysis, as well as ¹H and ¹³C NMR spectroscopy it was concluded that the glucomannan has an α-(1→6)-linked D-mannopyranosyl backbone having most residues (about 83%) substituted at O-2 with one, two, three or four D-mannopyranosyl units connected by α-(1→2) and α-(1→3) linkages. Moreover, an additional side chain with the α-D-Manp-(1→3)-D-Manp-(1→2)-D-Manp-(1→2)-D-Manp-D-Manp backbone structure in which α-D-glucopyranose residue is linked to O-2 of the mannopyranose unit next to the reducing end. Alkali treatment of glucomannanprotein in the presence of sodium borohydride showed that 87% serine and 83% threonine residues were glycosylated with mannose, mannobiose, and mannotriose.