AN EXTRACELLULAR GALACTOGLUCOXYLOMANNAN PROTEIN FROM THE YEAST Cryptococcus laurentii VAR. laurentii

An extracellular galactoglucoxylomannan protein composed of d-galactose, d-glucose, d-xylose and d-mannose in a 2.9:1.0:1.1:10.2 mole proportion has been isolated from culture medium of Cryptococcus laurentii var. laurentii. The polymer of number average molecular mass 19,000 contained 86% carbohydrates, 6.5% protein and 0.7% phosphorus. Results of structural analyses suggested a highly branched comb-like structure of the polysaccharide with a backbone composed of 6-linked α-d-Man residues. Mannose units of the backbone are highly branched at O-2, O-3, and O-4 by side chains composed mainly of 2-linked α-d-Man mostly in the form of dimers and trimers, and to a lesser amount as tetra- and pentamers. Galactosyl units were found to be mostly 6-linked with a very low degree of substitution. Mannose side chains are further branched with d-Xyl, d-Glc, and d-Gal residues preferably in β their forms. The protein part of the glycoprotein was O-glycosylated by mannose, mannobiose, and mannotetrose.