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Promiscuity in ligand-binding: The three-dimensional structure of a Piromyces carbohydrate-binding module, CBM29-2, in complex with cello-and mannohexaose

Lookup NU author(s): Dr David Bolam, Lorand Szabo, Dr Vincent McKie, Professor Harry Gilbert

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Abstract

Carbohydrate-protein recognition is central to many biological processes. Enzymes that act on polysaccharide substrates frequently contain noncatalytic domains, "carbohydrate-binding modules" (CBMs), that target the enzyme to the appropriate substrate, CBMs that recognize specific plant structural polysaccharides are often able to accommodate both the variable backbone and the side-chain decorations of heterogeneous ligands. "CBM29" modules, derived from a noncatalytic component of the Piromyces equi cellulase/hemicellulase complex, provide an example of this selective yet flexible recognition. They discriminate strongly against some polysaccharides while remaining relatively promiscuous toward both β-1,4-linked manno- and cello-oligosaccharides. This feature may reflect preferential, but flexible, targeting toward glucomannans in the plant cell wall. The three-dimensional structure of CBM29-2 and its complexes with cello- and mannohexaose reveal a β-jelly-roll topology, with an extended binding groove on the concave surface. The orientation of the aromatic residues complements the conformation of the target sugar polymer while accommodation of both manno- and glucoconfigured oligo- and polysaccharides is conferred by virtue of the plasticity of the direct interactions from their axial and equatorial 2-hydroxyls, respectively. Such flexible ligand recognition targets the anaerobic fungal complex to a range of different components in the plant cell wall and thus plays a pivotal role in the highly efficient degradation of this composite structure by the microbial eukaryote.


Publication metadata

Author(s): Charnock S, Bolam DN, Nurizzo D, Szabó L, McKie V, Gilbert HJ, Davies G

Publication type: Article

Publication status: Published

Journal: Proceedings of the National Academy of Sciences of the United States of America

Year: 2002

Volume: 99

Issue: 22

Pages: 14077-14082

ISSN (print): 0027-8424

ISSN (electronic): 1091-6490

Publisher: National Academy of Sciences

URL: http://dx.doi.org/10.1073/pnas.212516199

DOI: 10.1073/pnas.212516199

PubMed id: 12391332


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