Heteronuclear NMR studies of 13C-labeled yeast cell wall beta-glucan oligosaccharides

The structures of uniformly 13C-labeled beta-glucan octa- and undeca-oligosaccharides enzymatically prepared by the yeast cell wall glucanosyl transferase of Candida albicans were characterized by using a combination of HCCH-COSY, HCCH-TOCSY, and HMBC experiments. The oligosaccharide structures indicate that the cell wall glucanosyl transferase cleaves two glucosyl units from the reducing end of the initial linear beta(1-->3) penta-oligosaccharide and subsequently transfers the remainder to another oligosaccharide at the nonreducing end via a beta(1-->6) linkage. These results indicate that the combined action of cell wall glucanase and glucanosyl transferase activities could not only introduce intrachain beta(1-->6) linkages within a single glucan strand, but also result in cross-linking of two initially separate glucan strands with concurrent introduction of intrachain beta(1-->6) linkages. Since isolated fungal membranes only synthesize linear beta(1-->3) glucan strands, wall-associated enzymes probably participate in the assembly of the final wall glucan structure during cell growth and division.