Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada.
Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, V8W 3P6, Canada.
J Mol Biol. 2014 Feb 20;426(4):869-80. doi: 10.1016/j.jmb.2013.11.029. Epub 2013 Dec 8.
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.
碳水化合物结合模块 (CBMs) 是与碳水化合物活性酶 (CAZymes) 共同存在的辅助模块，其功能是介导母体酶与其碳水化合物底物的结合。CBM 家族 32 (CBM32) 是最具多样性的 CBM 家族之一，其成员通常存在于修饰真核聚糖的细菌 CAZymes 中。例如，家族 84 糖苷水解酶的假定 μ-毒素 CpGH84A，它由一个 N 端假定的 β-N-乙酰氨基葡萄糖苷酶催化模块和四个串联的 CBM32 组成。在这里，我们报告了 CpGH84A CBM32-1 对半乳糖的独特识别模式。基于溶液 NMR 的 CpGH84A CBM32-1 分析表明，位于 CBM 顶点的有序环中存在一个不同的残基亚组，赋予了对半乳糖构型糖半乳糖、GalNAc 和 LacNAc 的特异性，这与典型的半乳糖结合 CBM32 不同。这项研究展示了该 CBM 家族在配体结合方面的令人印象深刻的可变性，并深入了解了这些模块在 CAZymes 与真核聚糖相互作用中的作用不断增加。
