A Secreted β -glucan-branching Enzyme from Candida albicans

A M_r 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 M_r 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 M_r 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.