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Lookup NU author(s): Dr Aurore Labourel,
Dr Lucy Crouch,
Dr Adam Jackson,
Dr Artur Rogowski,
Dr Joseph Gray,
Emeritus Professor Harry Gilbert,
Dr Arnaud Basle,
Dr Fiona Cuskin
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
The enzymatic degradation of plant cell walls is an important biological process of increasing environmental and industrial significance. Xylan, a major component of the plant cell wall, consists of a backbone of -1,4-xylose (Xylp) units that are often decorated with arabinofuranose (Araf) side chains. A large penta-modular enzyme, CtXyl5A, was shown previously to specifically target arabinoxylans. The mechanism of substrate recognition displayed by the enzyme, however, remains unclear. Here we report the crystal structure of the arabinoxylanase and the enzyme in complex with ligands. The data showed that four of the protein modules adopt a rigid structure, which stabilizes the catalytic domain. The C-terminal non-catalytic carbohydrate binding module could not be observed in the crystal structure, suggesting positional flexibility. The structure of the enzyme in complex with Xylp--1,4-Xylp--1,4-Xylp-[-1,3-Araf]--1,4-Xylp showed that the Araf decoration linked O-3 to the xylose in the active site is located in the pocket (-2* subsite) that abuts onto the catalytic center. The -2* subsite can also bind to Xylp and Arap, explaining why the enzyme can utilize xylose and arabinose as specificity determinants. Alanine substitution of Glu(68), Tyr(92), or Asn(139), which interact with arabinose and xylose side chains at the -2* subsite, abrogates catalytic activity. Distal to the active site, the xylan backbone makes limited apolar contacts with the enzyme, and the hydroxyls are solvent-exposed. This explains why CtXyl5A is capable of hydrolyzing xylans that are extensively decorated and that are recalcitrant to classic endo-xylanase attack.
Author(s): Labourel A, Crouch LI, Bras JLA, Jackson A, Rogowski A, Gray J, Yadav MP, Henrissat B, Fontes CMGA, Gilbert HJ, Najmudin S, Basle A, Cuskin F
Publication type: Article
Publication status: Published
Journal: Journal of Biological Chemistry
Print publication date: 14/10/2016
Online publication date: 16/08/2016
Acceptance date: 02/04/2016
Date deposited: 03/01/2017
ISSN (print): 0021-9258
ISSN (electronic): 1083-351X
Publisher: The American Society for Biochemistry and Molecular Biology, Inc.
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