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An evolutionarily distinct family of polysaccharide lyases removes rhamnose capping of complex arabinogalactan proteins

Lookup NU author(s): Dr Jose Munoz Munoz, Dr Alan Cartmell, Dr Arnaud Basle, Emeritus Professor Harry Gilbert

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Abstract

© 2017 by The American Society for Biochemistry and Molecular Biology, Inc. The human gut microbiota utilizes complex carbohydrates as major nutrients. The requirement for efficient glycan degrading systems exerts a major selection pressure on this microbial community. Thus, we propose that this microbial ecosystem represents a substantial resource for discovering novel carbohydrate active enzymes. To test this hypothesis we screened the potential enzymatic functions of hypothetical proteins encoded by genes of Bacteroides thetaiotaomicron that were up-regulated by arabinogalactan proteins or AGPs. Although AGPs are ubiquitous in plants, there is a paucity of information on their detailed structure, the function of these glycans in planta, and the mechanisms by which they are depolymerized in microbial ecosystems. Here we have discovered a new polysaccharide lyase family that is specific for the L-rhamnose-1,4-D-glucuronic acid linkage that caps the side chains of complex AGPs. The reaction product generated by the lyase, 4,5-unsaturated uronic acid, is removed from AGP by a glycoside hydrolase located in family GH105, producing the final product 4-deoxy--L-threo-hex-4-enepyranosyl-uronic acid. The crystal structure of a member of the novel lyase family revealed a catalytic domain that displays an (/)6 barrel-fold. In the center of the barrel is a deep pocket, which, based on mutagenesis data and amino acid conservation, comprises the active site of the lyase. A tyrosine is the proposed catalytic base in the -elimination reaction. This study illustrates how highly complex glycans can be used as a scaffold to discover new enzyme families within microbial ecosystems where carbohydrate metabolism is a major evolutionary driver.

Publication metadata

Author(s): Munoz-Munoz J, Cartmell A, Terrapon N, Basle A, Henrissat B, Gilbert HJ

Publication type: Article

Publication status: Published

Journal: Journal of Biological Chemistry

Year: 2017

Volume: 292

Issue: 32

Pages: 13271-13283

Print publication date: 11/08/2017

Online publication date: 21/06/2017

Acceptance date: 02/04/2016

ISSN (print): 0021-9258

ISSN (electronic): 1083-351X

Publisher: American Society for Biochemistry and Molecular Biology Inc.

URL: https://doi.org/10.1074/jbc.M117.794578

DOI: 10.1074/jbc.M117.794578

PubMed id: 28637865

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