Structure of the cell wall proteogalactomannan from Neurospora crassa. I. Purification of the proteoheteroglycan and characterization of alkali-labile oligosaccharides.

Proteoheteroglycan (PHG) was prepared from Neurospora crassa cells by extraction with hot water followed by cetyltrimethylammoniumbromide fractionation. The polymer was purified by DEAE-cellulose chromatography followed by gel filtrations. The PHG was fractionated into five subfractions containing carbohydrate (65-88%), protein (19-36%), and a trace amount of phosphate (0.3-1.9%). The sugar compositions of the fractions were similar to each other (D-mannose, 47-60%, D-galactose, 35-50%, D-glucose, 2-5%) while the fractions showed significant heterogeneity in molecular size. Mild alkali treatment of the PHG in the presence of sodium borohydride yielded three kinds of reduced oligosaccharides. Structural studies using a methylation-GC-MS method, and proton and carbon NMR indicated that the tetrasaccharide fragment is beta-D-Galf(1-5)-beta-D-Galf(1-2)-alpha-D-Manp(1-2)man nitol, the trisaccharide is beta-D-Galf(1-2)-alpha-D-Manp(1-2)mannitol, and the disaccharide is alpha-D-Manp(1-2)mannitol.