SUGAR AND SIGNAL-TRANSDUCER BINDING-SITES OF THE ESCHERICHIA-COLI GALACTOSE CHEMORECEPTOR PROTEIN
SUGAR AND SIGNAL-TRANSDUCER BINDING-SITES OF THE ESCHERICHIA-COLI GALACTOSE CHEMORECEPTOR PROTEIN
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DOI：
10.1126/science.3057628
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发表时间：
1988-12-02
期刊：
影响因子：
56.9
通讯作者：
QUIOCHO, FA
中科院分区：
文献类型：
--
作者：
VYAS, NK;VYAS, MN;QUIOCHO, FA
大肠杆菌的 D-半乳糖结合（或化学感受器）蛋白充当半乳糖和葡萄糖趋化性以及两种糖的高亲和力主动转运的初始成分。野生型和从趋化性缺陷但完全具有运输能力的菌株中分离出的突变蛋白的配体形式的精细X射线结构提供了糖结合位点和与Trg跨膜信号转导器相互作用的位点的分子视图。糖结合位点的几何形状位于双叶蛋白两个叶之间的裂隙中，其新颖之处在于它被设计用于紧密结合和隔离α。或.beta。 4-差向异构体半乳糖和葡萄糖的 D-立体异构体的端基异构体。结合特异性和亲和力主要由极性平面侧链残基赋予，这些残基与糖底物形成复杂的合作和双齿氢键网络，其次由夹在吡喃糖环之间的芳香族残基赋予。每对异头羟基和差向异构羟基均由不同的 Asp 残基识别。与换能器相互作用的位置约为18.ANG。来自糖结合位点。该位点的 Gly74 突变为天冬氨酸，伴随着局部有序水结构的显着变化，导致与跨膜信号转导器缺乏有效的相互作用。
D-Galactose-binding (or chemoreceptor) protein of Escherichia coli serves as an initial component for both chemotaxis towards galactose and glucose and high-affinity active transport of the two sugars. Well-refined x-ray structures of the liganded forms of the wild-type and a mutant protein isolated from a strain defective in chemotaxis but fully competent in transport have provided a molecular view of the sugar-binding site and of a site for interacting with the Trg transmembrane signal transducer. The geometry of the sugar-binding site, located in the cleft between the two lobes of the bilobate protein, is novel in that it is designed for tight binding and sequestering of either the .alpha. or .beta. anomer of the D-stereoisomer of the 4-epimers galactose and glucose. Binding specificity and affinity are conferred primarily by polar planar side-chain residues that form intricate networks of cooperative and bidentate hydrogen bonds with the sugar substrates, and secondarily by aromatic residues that sandwich the pyranose ring. Each of the pairs of anomeric hydroxyls and epimeric hydroxyls is recognized by a distinct Asp residue. The site for interaction with the transducer is about 18 .ANG. from the sugar-binding site. Mutation of Gly74 to Asp at this site, concomitant with considerable changes in the local ordered water structures, contributes to the lack of productive interactions with the transmembrane signal transducer.