Biochemistry and Microbiology, University of Victoria, Victoria, BC, V8W 3P6, Canada.
Curr Opin Struct Biol. 2012 Oct;22(5):570-7. doi: 10.1016/j.sbi.2012.07.009. Epub 2012 Aug 1.
Mammalian glycans are often very complex and consequently both commensal bacteria and bacterial pathogens have developed specialized and often elaborate carbohydrate-active enzyme (CAZyme) systems to interact with these sugars. These enzymes are frequently multimodular, with modular functions most often conferring catalysis (glycoside hydrolase catalytic modules) or carbohydrate-binding (carbohydrate-binding modules or CBMs). Structure-function studies of five CBM families are revealing specificities for complex mammalian carbohydrates. Three of these CBM families (32, 47, and 51) show significant structural identity between their β-sandwich folds, suggesting a shared evolutionary precursor, but have divergent binding specificities. The family 40 and 41 CBMs recognize sialic acid and glycogen, respectively, through different modes of sugar binding, though they also adopt all β-structure folds. A structural view of new models generated for complete CAZymes suggests three distinct modes of CBM deployment: (i) formation of the catalytic site, (ii) coordinated catalysis and binding, and (iii) general substrate adherence.
哺乳动物糖链通常非常复杂，因此共生菌和病原菌都进化出了专门的、往往十分精巧的碳水化合物活性酶（CAZyme）系统来与这些糖相互作用。这些酶通常是多模块的，模块功能通常赋予其催化（糖苷水解酶催化模块）或碳水化合物结合（碳水化合物结合模块或 CBMs）功能。对五个 CBM 家族的结构-功能研究揭示了它们对复杂哺乳动物碳水化合物的特异性。这三个 CBM 家族（32、47 和 51）在它们的β-三明治折叠之间显示出显著的结构同一性，表明存在共享的进化前体，但具有不同的结合特异性。家族 40 和 41 CBM 通过不同的糖结合模式分别识别唾液酸和糖原，尽管它们也采用所有的β-结构折叠。对完整 CAZymes 生成的新模型的结构观察表明，CBM 有三种不同的部署模式：（i）形成催化位点，（ii）协调催化和结合，以及（iii）一般的底物附着。
