The structure of cell wall a-glucan from fission yeast

Morphology and structural integrity of fungal cells depend on cell wall polysaccharides. The chemical structure and bio-synthesis of two types of these polysaccharides, chitin and (1!3)-b-glucan, have been studied extensively, whereas little is known about a-glucan. Here we describe the chemical structure of a-glucan isolated from wild-type and mutant cell walls of the fission yeast Schizosaccharomyces pombe. Wild-type a-glucan was found to consist of a single popula-tion of linear glucose polymers, ~260 residues in length. These glucose polymers were composed of two interconnected linear chains, each consisting of ~120 (1!3)-linked a-D-glucose residues and some (1!4)-linked a-D-glucose residues at the reducing end. By contrast, a-glucan of an a-glucan synthase mutant with an aberrant cell morphology and reduced a-glucan levels consisted of a single chain only. We propose that a-glucan biosynthesis involves an ordered series of events, whereby two a-glucan chains are coupled to create mature cell wall a-glucan. This mature form of cell wall a-glucan is essential for fission-yeast morphogenesis. Key words: a-glucan/cell wall/fission yeast/morphogenesis/ polysaccharide