Analysis of a New Family of Widely Distributed Metal-independent α-Mannosidases Provides Unique Insight into the Processing of N-Linked Glycans
Analysis of a New Family of Widely Distributed Metal-independent α-Mannosidases Provides Unique Insight into the Processing of N-Linked Glycans
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DOI：
10.1074/jbc.m111.223172
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发表时间：
2011-04-29
影响因子：
4.8
通讯作者：
Boraston, Alisdair B.
中科院分区：
文献类型：
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作者：
Gregg, Katie J.;Zandberg, Wesley F.;Boraston, Alisdair B.
α-甘露糖苷酶对 N-聚糖的修饰是一个与许多重要的生物学过程相关的过程，包括微生物病原体的感染和微生物共生体的定植。目前，所描述的对α1,6-甘露糖键特异的甘露糖苷酶的数量非常有限。通过对两种序列相关酶（一种来自肺炎链球菌 (SpGH125) 和一种来自产气荚膜梭菌 (CpGH125)）的结构和功能分析，鉴定并表征了新的糖苷水解酶家族 GH125。 SpGH125 和 CpGH125 的分析表明它们具有外切-α 1,6-甘露糖苷酶活性，与去除了 α 1,3-甘露糖分支的 N 连接聚糖的特异性一致。以脱辅基、抑制剂结合和底物结合形式获得的 SpGH125 和 CpGH125 的 X 射线晶体结构提供了机械和分子方面的见解，了解这些采用 (α/α)(6) 折叠的蛋白质如何通过反转、不依赖金属的催化机制识别和水解 α 1,6-甘露糖苷键。 GH125 蛋白的系统发育分析表明，这是一个相对较大且分布广泛的家族，常见于细菌病原体、细菌人类肠道共生体和各种真菌中。基于这些研究，我们预测该酶家族将主要包含此类外切-α 1,6-甘露糖苷酶。
The modification of N-glycans by alpha-mannosidases is a process that is relevant to a large number of biologically important processes, including infection by microbial pathogens and colonization by microbial symbionts. At present, the described mannosidases specific for alpha 1,6-mannose linkages are very limited in number. Through structural and functional analysis of two sequence-related enzymes, one from Streptococcus pneumoniae (SpGH125) and one from Clostridium perfringens (CpGH125), a new glycoside hydrolase family, GH125, is identified and characterized. Analysis of SpGH125 and CpGH125 reveal them to have exo-alpha 1,6-mannosidase activity consistent with specificity for N-linked glycans having their alpha 1,3-mannose branches removed. The x-ray crystal structures of SpGH125 and CpGH125 obtained in apo-, inhibitor-bound, and substrate-Bound forms provide both mechanistic and molecular insight into how these proteins, which adopt an (alpha/alpha)(6)-fold, recognize and hydrolyze the alpha 1,6-mannosidic bond by an inverting, metal-independent catalytic mechanism. A phylogenetic analysis of GH125 proteins reveals this to be a relatively large and widespread family found frequently in bacterial pathogens, bacterial human gut symbionts, and a variety of fungi. Based on these studies we predict this family of enzymes will primarily comprise such exo-alpha 1,6-mannosidases.