拟杆菌的碳水化合物结合模块的结构为人类微生物组对复杂果胶多糖的识别提供了新的见解

IF 3.5 Q2 BIOCHEMISTRY & MOLECULAR BIOLOGY
Filipa Trovão , Viviana G. Correia , Frederico M. Lourenço , Diana O. Ribeiro , Ana Luísa Carvalho , Angelina S. Palma , Benedita A. Pinheiro
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引用次数: 0

摘要

拟杆菌群(Bacteroides thetaiotaomicron)已经开发出一系列酶,能够克服空间限制并以顺序的方式降解复杂的鼠李糖半乳葡聚糖II (RG-II)多糖。BT0996蛋白在RG-II解聚合的初始阶段起作用,其两个催化模块从RG-II侧链A和b中去除末端单糖。BT0996是模块化的,具有三个假定的碳水化合物结合模块(CBMs),其在RG-II降解中的作用尚不清楚。在这里,我们展示了该模块在c端域的特征,我们将其命名为BT0996-C。通过x射线晶体学获得的高分辨率结构显示,该蛋白具有典型的β-三明治折叠结构,与归属于家族6和35的CBMs结构相似。其显著特征是:1)在BT0996-C表面存在几个带电残基,形成一个大而宽的富含正赖氨酸的斑块,包含假定的结合位点;2)缺乏在家族6和35的CBMs中观察到的高度保守的结合位点特征,如A区色氨酸和C区天冬酰胺。这些发现暗示BT0996-C的结合模式尚未在其同源物中观察到。与此相一致的是,碳水化合物微阵列和微尺度热电泳显示BT0996-C能够结合α1-4连接的聚半乳糖醛酸,并且静电相互作用对于阴离子多糖的识别是必不可少的。这些结果支持了BT0996- c可能通过结合聚半乳糖醛酸主链序列来增强BT0996催化模块对RG-II复杂结构的作用的假设。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

The structure of a Bacteroides thetaiotaomicron carbohydrate-binding module provides new insight into the recognition of complex pectic polysaccharides by the human microbiome

The structure of a Bacteroides thetaiotaomicron carbohydrate-binding module provides new insight into the recognition of complex pectic polysaccharides by the human microbiome

The Bacteroides thetaiotaomicron has developed a consortium of enzymes capable of overcoming steric constraints and degrading, in a sequential manner, the complex rhamnogalacturonan II (RG-II) polysaccharide. BT0996 protein acts in the initial stages of the RG-II depolymerisation, where its two catalytic modules remove the terminal monosaccharides from RG-II side chains A and B. BT0996 is modular and has three putative carbohydrate-binding modules (CBMs) for which the roles in the RG-II degradation are unknown. Here, we present the characterisation of the module at the C-terminal domain, which we designated BT0996-C. The high-resolution structure obtained by X-ray crystallography reveals that the protein displays a typical β-sandwich fold with structural similarity to CBMs assigned to families 6 and 35. The distinctive features are: 1) the presence of several charged residues at the BT0996-C surface creating a large, broad positive lysine-rich patch that encompasses the putative binding site; and 2) the absence of the highly conserved binding-site signatures observed in CBMs from families 6 and 35, such as region A tryptophan and region C asparagine. These findings hint at a binding mode of BT0996-C not yet observed in its homologues. In line with this, carbohydrate microarrays and microscale thermophoresis show the ability of BT0996-C to bind α1-4-linked polygalacturonic acid, and that electrostatic interactions are essential for the recognition of the anionic polysaccharide. The results support the hypothesis that BT0996-C may have evolved to potentiate the action of BT0996 catalytic modules on the complex structure of RG-II by binding to the polygalacturonic acid backbone sequence.

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来源期刊
Journal of Structural Biology: X
Journal of Structural Biology: X Biochemistry, Genetics and Molecular Biology-Structural Biology
CiteScore
6.50
自引率
0.00%
发文量
20
审稿时长
62 days
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