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Lookup NU author(s): Dr Zak McIver, Dr Arnaud Basle
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2025 The AuthorsRhamnogalacturonan II is one of the most complex plant cell wall carbohydrates and is composed of 13 different sugars and 21 different glycosidic linkages. It is abundant in fruit and indulgence foods, such as chocolate and wine, making it common in the human diet. The human colonic commensal Bacteroides thetaiotaomicron expresses a consortium of 22 enzymes to metabolize rhamnogalacturonan II, some of which exclusively target sugars unique to rhamnogalacturonan II. Several of these enzyme families remain poorly described, and, consequently, our knowledge of rhamnogalacturonan II metabolism is limited. Chief among the poorly understood activities is glycoside hydrolase (GH) family 139, which targets α1,2-2O-methyl L-fucoside linkages, a sugar residue not found in any other plant cell wall complex glycans. Although the founding enzyme BT0984 was placed in the RG-II degradative pathway, no GH139 structure or catalytic blueprint had been available. We report the crystal structures of BT0984 and a second homolog revealing that the family operates with inverting stereochemistry. Using these data, we undertook a mutagenic strategy, backed by molecular dynamics, to identify the important substrate binding and catalytic residues, mapping these residues throughout the GH139 family revealing the importance of the O2 methyl interaction of the substrate. We propose a catalytic mechanism that uses a non-canonical Asn as a catalytic base and shares similarity with L-fucosidases/L-galactosidases of family GH95.
Author(s): McIver Z, Moraleda-Montoya A, Chen Z, Epa R, Starns D, Davy M, Garcia-Alija M, Basle A, Schubert M, Ndeh D, Trastoy B, Williams SJ, Guerin ME, Cartmell A
Publication type: Article
Publication status: Published
Journal: Journal of Biological Chemistry
Year: 2025
Volume: 301
Issue: 8
Print publication date: 01/08/2025
Online publication date: 20/06/2025
Acceptance date: 06/06/2025
Date deposited: 28/07/2025
ISSN (print): 0021-9258
ISSN (electronic): 1083-351X
Publisher: American Society for Biochemistry and Molecular Biology Inc.
URL: https://doi.org/10.1016/j.jbc.2025.110407
DOI: 10.1016/j.jbc.2025.110407
Data Access Statement: The crystal structure datasets generated have been deposited in the Protein Data Bank (PDB) under the following accession numbers: 9HYQ and 9HMB. Information on all other data and materials is contained within the main manuscript and Supplemental Information.
PubMed id: 40544995
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