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J. Biol. Chem., Vol. 283, Issue 18, 12604-12613, May 2, 2008

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Divergent Modes of Glycan Recognition by a New Family of Carbohydrate-binding Modules^*

From the Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia V8W 3P6, Canada

The genomes of myonecrotic Clostridium perfringens isolates contain genes encoding a large and fascinating array of highly modular glycoside hydrolase enzymes. Although the catalytic activities of many of these enzymes are somewhat predictable based on their amino acid sequences, the functions of their abundant ancillary modules are not and remain poorly studied. Here, we present the structural and functional analysis of a new family of ancillary carbohydrate-binding modules (CBMs), CBM51, which was previously annotated in data bases as the novel putative CBM domain. The high resolution crystal structures of two CBM51 members, GH95CBM51 and GH98CBM51, from a putative family 95 -fucosidase and from a family 98 blood group A/B antigen-specific endo-β-galactosidase, respectively, showed them to have highly similar β-sandwich folds. However, GH95CBM51 was shown by glycan microarray screening, isothermal titration calorimetry, and x-ray crystallography to bind galactose residues, whereas the same analyses of GH98CBM51 revealed specificity for the blood group A/B antigens through non-conserved interactions. Overall, this work identifies a new family of CBMs with many members having apparent specificity for eukaryotic glycans, in keeping with the glycan-rich environment C. perfringens would experience in its host. However, a wider bioinformatic analysis of this CBM family also indicated a large number of members in non-pathogenic environmental bacteria, suggesting a role in the recognition of environmental glycans.

Received for publication, December 4, 2007 , and in revised form, February 13, 2008.

The atomic coordinates and structure factors (codes 2vmg, 2vmh, 2vmi, 2vnr, 2vng, and 2vno) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^* This work was supported in part by a grant from the Canadian Institutes of Health Research. The resources and collaborative efforts provided by the Consortium for Functional Glycomics were supported by NIGMS Grant GM62116 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. 1 and 2.

This article was selected as a Paper of the Week.

¹ Supported by a University of Victoria graduate fellowship.

² Canada Research Chair in Molecular Interactions and Michael Smith Foundation for Health Research Scholar. To whom correspondence should be addressed: Dept. of Biochemistry and Microbiology, University of Victoria, P. O. Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada. Tel.: 250-472-4168; Fax: 250-721-8855; E-mail: boraston{at}uvic.ca.

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				J. J. Adams, K. Gregg, E. A. Bayer, A. B. Boraston, and S. P. Smith Structural basis of Clostridium perfringens toxin complex formation PNAS, August 26, 2008; 105(34): 12194 - 12199. [Abstract] [Full Text] [PDF]