Multiple Mannosyl Transferases in Cryptococcus laurentii

A particle-bound enzyme preparation from the fungus imperfectus Cryptococcus laurentii var. flavescens (NRRL Y-1401) catalyzes transfer of mannosyl units from GDP-mannose to mono- and oligosaccharide acceptors. Four separate enzymes can be differentiated by some or all of the following criteria: pH optimum, Km values for GDP-mannose, acceptor specificity, heat lability, metal ion requirement, and cross inhibition. These four enzymes catalyze the formation of four distinct mannosyl linkages, namely mannosyl-α-1,2-mannosyl (Enzyme I); mannosyl-α-1, 6-mannosyl (Enzyme II); mannosyl-α-1,3-mannosyl (Enzyme III); mannosyl-xylosyl (Enzyme IV). The occurrence of at least two of these linkages in cell wall heteropolysaccharides of C. laurentii suggests involvement of at least two, and possibly all four of these enzymes in cell wall biosynthesis of this organism.