Please use this identifier to cite or link to this item:
https://hdl.handle.net/2440/13567
Citations | ||
Scopus | Web of Science® | Altmetric |
---|---|---|
?
|
?
|
Type: | Journal article |
Title: | Catalytic mechanisms and reaction intermediates along the hydrolytic pathway of a plant beta-D-glucan glucohydrolase |
Author: | Hrmova, M. Varghese, J. De Gori, R. Smith, B. Driguez, H. Fincher, G. |
Citation: | Structure, 2001; 9(11):1005-1016 |
Publisher: | Cell Press |
Issue Date: | 2001 |
ISSN: | 0969-2126 1878-4186 |
Statement of Responsibility: | Maria Hrmova, Joseph N. Varghese, Ross De Gori, Brian J. Smith, Hugues Driguez and Geoffrey B. Fincher |
Abstract: | Background: Barley β-D-glucan glucohydrolases represent family 3 glycoside hydrolases that catalyze the hydrolytic removal of nonreducing glucosyl residues from β-D-glucans and β-D-glucooligosaccharides. After hydrolysis is completed, glucose remains bound in the active site. Results: When conduritol B epoxide and 2′, 4′-dinitrophenyl 2-deoxy-2-fluoro-β-D-glucopyranoside are diffused into enzyme crystals, they displace the bound glucose and form covalent glycosyl-enzyme complexes through the Oδ1 of D285, which is thereby identified as the catalytic nucleophile. A nonhydrolyzable S-glycosyl analog, 4I, 4III, 4V-S-trithiocellohexaose, also diffuses into the active site, and a S-cellobioside moiety positions itself at the −1 and +1 subsites. The glycosidic S atom of the S-cellobioside moiety forms a short contact (2.75 Å) with the Oε2 of E491, which is likely to be the catalytic acid/base. The glucopyranosyl residues of the S-cellobioside moiety are not distorted from the low-energy 4C1 conformation, but the glucopyranosyl ring at the +1 subsite is rotated and translated about the linkage. Conclusions: X-ray crystallography is used to define the three key intermediates during catalysis by β-D-glucan glucohydrolase. Before a new hydrolytic event begins, the bound product (glucose) from the previous catalytic reaction is displaced by the incoming substrate, and a new enzyme-substrate complex is formed. The second stage of the hydrolytic pathway involves glycosidic bond cleavage, which proceeds through a double-displacement reaction mechanism. The crystallographic analysis of the S-cellobioside-enzyme complex with quantum mechanical modeling suggests that the complex might mimic the oxonium intermediate rather than the enzyme-substrate complex. Author Keywords: catalytic acid/base; catalytic nucleophile; enzyme kinetics; family 3 glycoside hydrolases; mechanism-based inhibitors; S-glycosyl substrate analog. |
Keywords: | catalytic acid/base catalytic nucleophile enzyme kinetics family 3 glycoside hydrolases mechanism-based inhibitors S-glycosyl substrate analog |
DOI: | 10.1016/S0969-2126(01)00673-6 |
Published version: | http://www.cell.com/structure/retrieve/pii/S0969212601006736 |
Appears in Collections: | Agriculture, Food and Wine publications Aurora harvest 7 |
Files in This Item:
There are no files associated with this item.
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.