Elucidation of cellobiose metabolic pathway in Trichoderma reesei

里氏木霉(Trichoderma Reesei)以产纤维素酶著称，在纤维素上生长时表达三种糖苷酶，其中一种是分泌β-葡萄糖苷酶(Cel3A)，另一种是胞内Cel1a和Cel3c。为了阐明这些BGL的生理作用，我们研究了异源宿主产生的重组酶的酶学性质。此外，我们构建了相应bgl基因的缺失突变体，并对突变体在纤维素和纤维二糖上生长时的生物量以及纤维素酶和bgl的活性进行了表征。结果表明，Cel3A和Cel3C对纤维二糖的催化活性高于PNP-GLC，而Cel1a对纤维二糖的催化活性高于PNP-GLC。突变体的胞内和胞外BGL活性反映了各自酶的底物专一性。我们推测Cel1a在纤维二糖代谢中起关键作用，而BGL不直接参与纤维素酶的诱导。当里氏木霉生长在纤维二糖上时，除了Cel3A外，另一种Bgl(S)似乎也有表达和分泌。

Trichoderma reesei, which is well known to produce large amount of cellulases, expresses threeβ-glucosidases(BGLs), one of which is secreted Cel3A and the other are intracellular Cel1A and Cel3C, when grown on cellulose. To elucidate the physiological roles of these BGLs, we investigated the enzymatic properties of the recombinant enzymes produced by heterologous hosts. Furthermore, we constructed the deficient mutants of the corresponding BGL genes and characterized the amount of biomass and the cellulase and BGL activities of the mutants when grown on cellulose or cellobiose. The results demonstrated that Cel3A and Cel3C preferred pNP-Glc to cellobiose as the substrate, whereas Cel1A had higher activity for cellobiose than that for pNP-Glc. The intracellular and extracellular BGL activities of the mutants reflected the substrate specificity of the respective enzymes. We assumed that Cel1A plays the key role in cellobiose metabolism and the BGLs would not directly involve in cellulase induction. When T. reesei is grown on cellobiose, the other BGL(s) besides Cel3A seems to be expressed and secreted.