Purification of exo-1,3-beta-glucanase, a new extracellular glucanolytic enzyme from Talaromyces emersonii

The moderately thermophilic aerobic ascomycete Talaromyces emersonii secretes, under selected growth conditions, several beta-glucan hydrolases including an exo-1,3-beta-glucanase. This enzyme was purified to apparent homogeneity in order to characterise its biochemical properties and investigate hydrolysis of different beta-glucans, including laminaran, a 1,3-beta-glucan from brown algae. The native enzyme is monomeric with a molecular mass of similar to 40 kDa and a pI value of 4.3, and is active over broad ranges of pH and temperature, with optimum activity observed at pH 5.4 and 65 A degrees C. At pH 5.0, the enzyme displays strict specificity for laminaran (apparent K (m) 1.66 mg mL(-1); V (max) 7.69 IU mL(-1)) and laminari-oligosaccharides and did not yield activity against 1,4-beta-glucans, 1,3;1,4-beta-glucans or 4-nitrophenyl- and methylumbelliferyl-beta-d-glucopyranosides. Analysis of hydrolysis products formed during time-course hydrolysis of laminaran by high-performance anion exchange chromatography with pulsed amperometric detection revealed a strict exo mode of action, with glucose being the sole reaction product even at the initial stages of hydrolysis. The T. emersonii exo-1,3-beta-glucanase was inhibited by glucono-delta-lactone (K (i) 1.25 mM) but at significantly higher concentrations than typically inhibitory for exo-glycosidases such as beta-glucosidase. 'De novo' sequence analysis of the purified enzyme suggests that it belongs to family GH5 of the glycosyl hydrolase superfamily. The results clearly show that the exo-1,3-beta-glucanase is yet another novel enzyme present in the beta-glucanolytic enzyme system of T. emersonii.