A Secreted β -glucan-branching Enzyme from Candida albicans
A Mr 34000 wall protein was isolated as a by-product of the purification of an endo-(1-3)-β -glucanase from the culture filtrate of Candida albicans. The purified fraction contained no exo- or endo-β -glucanase activity, and analysis by SDS poly-acrylamide gel electrophoresis (SDS-PAGE) showed one protein band at Mr 34000. Analysis by gel filtration high performance liquid chromatography (HPLC) of reaction products from incubations of the protein fraction with laminarioligosaccharides of five glucosyl units or greater revealed a unique glucanosyl transferase activity. The enzyme specifically cleaved laminaribiaose (G2) from the reducing-end of a linear β -(1-3)-glucan and transferred the remainder to another laminari-oligosaccharide. The reaction with laminaripentaose (G5) produced G2 and a product eluting at the position of G8. Analysis of the latter transferase product by 13C-and 1H-nuclear magnetic resonance (NMR) spectroscopy shows it to be a branched molecule containing a β -(1-3)-β -(1-6)-branchpoint. It is suggested that the Mr 34000 wall protein is a glucan branching enzyme, perhaps the key enzyme responsible for the transformation of the initial linear β -1-3)-glucan into the branched β -(1-3)-β -1-6)-glucan as found in the cell wall of C. albicans.
Proceedings of the Royal Society of London Series B
- Pub Date:
- November 1991