DIFFERENTIAL PATTERNS OF ACTIVITY DISPLAYED BY 2 EXO-BETA-1,3-GLUCANASES ASSOCIATED WITH THE ASPERGILLUS-FUMIGATUS CELL-WALL

Two exo-beta-1,3-glucanases (herein designated exoG-I and exoG-II) wer e isolated from the cell wall autolysate of the filamentous fungus Asp ergillus fumigatus and purified by ion-exchange, hydrophobic-interacti on, and gel filtration chromatographies, molecular masses estimated bu sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel fil tration chromatography were 82 kDa for the monomeric exoG-I and 230 kD a for the dimeric exoG-II, exoG-I and exoG-II were glycosylated, and N glycans accounted, respectively, for 2 and 44 kDa. Their pH optimum i s 5.0. Their optimum temperatures are 55 degrees C for exoG-I and 65 d egrees C for exoG-II. By a sensitive colorimetric method and high-perf ormance anion-exchange chromatography for product analysis, two patter ns of exo-beta-1,3-glucanase activities were found. The 23O-kDa exoG-I I enzyme acts on p-nitrophenyl-beta-D-glucoside, beta-1,6-glucan, and beta-1,3-glucan. This activity, which retains the anomeric configurati on of glucose released, presented a multichain pattern of attack of ti le glucan chains and a decrease in the maximum initial velocity (V-m) with the increasing size of the substrate, In contrast, the 82-kDa exo G-I, which inverts the anomeric configuration of the glucose released, hydrolyzed exclusively the beta-1,3-glucan chain with a minimal subst rate size of 4 glucose residues, This enzyme presented a repetitive-at tack pattern, characterized by an increase in V-m with an increase in substrate size and by a degradation of the glucan chain until it reach ed laminaritetraose, the limit substrate size, The 82-kDa exoG-I and 2 30-kDa exoG-II enzymes correspond to a beta-1,3-glucan-glucohydrolase (EC 3.2.1.58) and to a beta-D-glucoside-glucohydrolase (EC 3.2.1.21), respectively. The occurrence and functions of these two classes of exo -beta-1,3-glucanases in other fungal species are discussed.