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An Unusual Mode of Galactose Recognition by a Family 32 Carbohydrate-Binding Module
Authors:Julie M. Grondin  Seth Chitayat  Elizabeth Ficko-Blean  Scott Houliston  Cheryl H. Arrowsmith  Alisdair B. Boraston  Steven P. Smith
Affiliation:1 Department of Biomedical and Molecular Sciences, Queen''s University, Kingston, Ontario, K7L 3N6, Canada;2 Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, V8W 3P6, Canada;3 Princess Margaret Cancer Centre and Department of Medical Biophysics, University of Toronto, Toronto, Ontario, M5G 1L7, Canada;4 Protein Function Discovery Group, Queen''s University, Kingston, Ontario, K7L 3N6, Canada
Abstract:Carbohydrate-binding modules (CBMs) are ancillary modules commonly associated with carbohydrate-active enzymes (CAZymes) that function to mediate the adherence of the parent enzyme to its carbohydrate substrates. CBM family 32 (CBM32) is one of the most diverse CBM families, whose members are commonly found in bacterial CAZymes that modify eukaryotic glycans. One such example is the putative μ-toxin, CpGH84A, of the family 84 glycoside hydrolases, which comprises an N-terminal putative β-N-acetylglucosaminidase catalytic module and four tandem CBM32s. Here, we report a unique mode of galactose recognition by the first CBM32, CBM32-1 from CpGH84A. Solution NMR-based analyses of CpGH84A CBM32-1 indicate a divergent subset of residues, located in ordered loops at the apex of the CBM, conferring specificity for the galacto-configured sugars galactose, GalNAc, and LacNAc that differs from those of the canonical galactose-binding CBM32s. This study showcases the impressive variability in ligand binding by this CBM family and offers insight into the growing role of these modules in the interaction of CAZymes with eukaryotic glycans.
Keywords:CBM, carbohydrate-binding module   CAZyme, carbohydrate-active enzyme   2D, two-dimensional   HSQC, heteronuclear single quantum coherence   NOE, nuclear Overhauser enhancement   NOESY, NOE spectroscopy   STD, saturation transfer difference
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