A novel beta-(1-3)-glucanosyltransferase from the cell wall of Aspergillus fumigatus

Cell wall transferases utilizing beta-(1-3)-glucan chains as substrates may play important roles in cell wall assembly and rearrangement, as beta-(1-3)-glucan is a major structural component of the cell wall of many fungi, A novel beta-(1-3)-glucanosyltransferase was purified to apparent homogeneity from an autolysate of the cell wall of Aspergillus fumigatus. The enzyme had a molecular mass of 49 kDa and contained approximately 5 kDa of N-linked carbohydrate. The enzyme catalyzed an initial endo-type splitting of a beta-(1-3) glucan molecule, followed by linkage of the newly generated reducing end to the nonreducing end of another beta-(13)-glucan molecule, Laminarioligosaccharides of size G(10) and greater were donor substrates for the transferase, Laminarioligosaccharides of size G(5) and greater formed accepters. The enzyme was able to reuse initial transferase products as donors and accepters in extended incubations, resulting in the formation of increasingly larger transferase products until they became insoluble. The major initial products from an incubation of the transferase with borohydride-reduced G(11) (rG(11)) were rG(6) and rG(16). H-1 MMR analysis of the rG(16) transferase product showed it was a laminarioligosaccharide, indicating that the enzyme forms a beta-(1-3)-linkage during transfer. The enzyme may have a key function in vivo by allowing the integration of newly synthesized glucan into the wall and promoting cell wall expansion during cell growth.