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The Mechanism by Which Arabinoxylanases Can Recognize Highly Decorated Xylans

Lookup NU author(s): Dr Aurore Labourel, Dr Lucy Crouch, Dr Adam Jackson, Dr Artur Rogowski, Dr Joseph Gray, Professor Harry Gilbert, Dr Arnaud Basle, Dr Fiona Cuskin

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

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.


Publication metadata

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

Year: 2016

Volume: 291

Issue: 42

Pages: 22149-22159

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.

URL: http://dx.doi.org/10.1074/jbc.M116.743948

DOI: 10.1074/jbc.M116.743948


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