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首页> 外文期刊>Journal of Molecular Biology >The B(12)-binding subunit of glutamate mutase from Clostridium tetanomorphum traps the nucleotide moiety of coenzyme B(12).
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The B(12)-binding subunit of glutamate mutase from Clostridium tetanomorphum traps the nucleotide moiety of coenzyme B(12).

机译：来自破伤风梭菌的谷氨酸突变酶的B（12）结合亚基捕获辅酶B（12）的核苷酸部分。

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Glutamate mutase from Clostridium tetanomorphum binds coenzyme B(12) in a base-off/His-on form, in which the nitrogenous ligand of the B(12)-nucleotide function is displaced from cobalt by a conserved histidine. The effect of binding the B(12)-nucleotide moiety to MutS, the B(12)-binding subunit of glutamate mutase, was investigated using NMR spectroscopic methods. Binding of the B(12)-nucleotide to MutS was determined to occur with K(d)=5.6(+/-0.7) mM and to be accompanied by a specific conformational change in the protein. The nucleotide binding cleft of the apo-protein, which is formed by a dynamic segment with propensity for partial alpha-helical conformation (the "nascent" alpha-helix), becomes completely structured upon binding of the B(12)-nucleotide, with formation of helix alpha1. In contrast, the segment containing the conserved residues of the B(12)-binding Asp-x-His-x-x-Gly motif remains highly dynamic in the protein/B(12)-nucleotide complex. From relaxation studies, the time constant tau, which characterizes the time scale for the formation of helix alpha1, was estimated to be about 30 micros (15)N and was the same in both, apo-protein and nucleotide-bound protein. Thus, the binding of the B(12)-nucleotide moiety does not significantly alter the kinetics of helix formation, but only shifts the equilibrium towards the structured fold. These results indicate MutS to be structured in such a way, as to be able to trap the nucleotide segment of the base-off form of coenzyme B(12) and provide, accordingly, the first structural clues as to how the process of B(12)-binding occurs. Copyright 2001 Academic Press.
机译：来自破伤风梭状芽孢杆菌的谷氨酸突变酶以碱基关闭/ His-on形式结合辅酶B（12），其中B（12）-核苷酸功能的含氮配体被保守的组氨酸从钴中置换出来。使用NMR光谱方法研究了将B（12）-核苷酸部分与MutS（谷氨酸突变酶的B（12）-结合亚基）结合的效果。确定B（12）核苷酸与MutS的结合发生在K（d）= 5.6（+/- 0.7）mM处，并伴随蛋白质中特定的构象变化。脱辅基蛋白的核苷酸结合裂隙是由具有部分α-螺旋构象倾向的动态片段（“新生的”α-螺旋）形成的，在结合了B（12）-核苷酸后，变得完全结构化。螺旋α1的形成。相反，含有B（12）-结合Asp-x-His-x-x-Gly基序的保守残基的片段在蛋白质/ B（12）-核苷酸复合物中仍保持高度动态。从弛豫研究中，表征螺旋α1形成的时间尺度的时间常数tau估计约为30微米（15）N，载脂蛋白和核苷酸结合蛋白中的常数相同。因此，B（12）-核苷酸部分的结合不会显着改变螺旋形成的动力学，而只会使平衡向结构化折叠方向移动。这些结果表明MutS的构建方式能够捕获辅酶B（12）的碱基关闭形式的核苷酸片段，并相应地提供有关B（ 12）绑定发生。版权所有2001学术出版社。

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