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Cellulase Cel7A from Trichoderma reesei is one of the most abundant and effective cellulases. Structural studies have established that Cel7A is a retaining glycosidase and it can processively hydrolyze cellobiose units from the reducing end of a cellulose chain. Here, to elucidate the mechanism of enzymatic catalysis of cellulase Cel7A, we carried out a multisized level theoretical study by performing MD, QM, and QM/MM calculations. At the accurate level of theory, we showed the mechanism details of the catalytic cycle, which involves the configuration inversion of the anomeric center twice: the first results in the glycosidic bond cleavage and the formation of covalent glycosyl-enzyme intermediate, and the second restores the anomeric carbon to its original configuration. Calculated results have provided detailed structural and energetic information about these two processes, both of which proceed according to a S(N)2-type-like mechanism via loose transition state structures. It is clearly indicated that the glycosidic bond hydrolysis involves the formation of a covalent glycosyl-enzyme intermediate, which has been identified as the minimum on the potential energy surface. At the catalytic active region, hydrogen bond interactions exist throughout the whole process of the catalytic cycle, which are of special importance for stabilizing the glycosyl-enzyme intermediate. The present results provide a clear paradigm of the mechanisms of general glycosidases, which hydrolyze the glycosidic bonds with net retention of the anomeric configuration.
State Key Laboratory of Microbial Technology and Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China.
This article was published in the following journal.
Name: The journal of physical chemistry. B
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A class of enzymes involved in the hydrolysis of the N-glycosidic bond of nitrogen-linked sugars.
An enzyme that catalyzes the HYDROLYSIS of the N-glycosidic bond between sugar phosphate backbone and URACIL residue during DNA synthesis.
An enzyme that removes THYMINE and URACIL bases mispaired with GUANINE through hydrolysis of their N-glycosidic bond. These mispaired nucleotides generally occur through the hydrolytic DEAMINATION of 5-METHYLCYTOSINE to thymine.
An endocellulase with specificity for the hydrolysis of 1,4-beta-glucosidic linkages in CELLULOSE, lichenin, and cereal beta-glucans.
A class of enzymes that catalyze the formation of a bond between two substrate molecules, coupled with the hydrolysis of a pyrophosphate bond in ATP or a similar energy donor. (Dorland, 28th ed) EC 6.
Enzymes are proteins that catalyze (i.e., increase the rates of) chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical re...