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首页> 外文期刊>Biochemistry >glmS Riboswitch Binding to the Glucosamine-6-phosphate α-Anomer Shifts the pK_a toward Neutrality
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glmS Riboswitch Binding to the Glucosamine-6-phosphate α-Anomer Shifts the pK_a toward Neutrality

机译：glmS核糖开关与6-磷酸氨基葡萄糖α-端基异构体的结合使pK_a向中性移动

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摘要

The glmS riboswitch regulates gene expression through a self-cleavage activity. The reaction is catalyzed with the assistance of the metabolite cofactor glucosamine-6- phosphate (GlcN6P), whose amino group is proposed to serve as the general acid during the reaction. This reaction is pH-dependent with a pKa that is lower than the observed pKa for the amine of GlcN6P in solution. GlcN6P, like other pyranose sugars, undergoes spontaneous and rapid interconversion between the α and β anomers at the C1 position. Here we demonstrate by NMR that the Bacillus anthracis glmS riboswitch selectively binds the α-anomer of GlcN6P with a maximum binding affinity of 0.36 mM and that binding is pH-dependent. We also report that the anomeric ratio between α and β is pHdependent and the pKas of the two amines differ by 0.5 pH units, α being the higher of the two (pKa = 8.3). The pH dependence of binding reveals a pKa of 6.7, suggesting that the glmS RNA reduces the pKa of the GlcN6P amine by 1.6 units in the ground state. We reevaluated previously obtained kinetic data and found the reaction pKa is 6.9, within error of the binding data. The data support a model where the reaction pKa corresponds to that of the GlcN6P amine. This observation has broader relevance for considering how the microenvironment of an RNA, despite its anionic character, can reduce the pKas of functional groups foruse in catalysis.
机译：glmS核糖开关通过自我切割活性调节基因表达。该反应在代谢物辅因子6-磷酸氨基葡萄糖（GlcN6P）的催化下进行，该氨基被提议在反应过程中用作一般酸。该反应是pH依赖性的，其pKa值低于溶液中GlcN6P的胺的pKa值。与其他吡喃糖一样，GlcN6P在C1位置的α和β端基异构体之间自发快速发生相互转化。在这里，我们通过NMR证明炭疽芽孢杆菌glmS核糖开关选择性结合GlcN6P的α-异头物，最大结合亲和力为0.36 mM，并且结合是pH依赖性的。我们还报告说，α和β之间的端基异构体比率是pH依赖性的，两种胺的pKas相差0.5个pH单位，α是二者中较高的一个（pKa = 8.3）。结合的pH依赖性显示pKa为6.7，表明glmS RNA在基态下将GlcN6P胺的pKa降低了1.6个单位。我们重新评估了先前获得的动力学数据，发现反应pKa为6.9，在结合数据的误差范围内。数据支持一种模型，其中反应pKa对应于GlcN6P胺的反应。考虑到RNA的微环境（尽管具有阴离子特性）如何减少催化中使用的官能团的pKas，这一发现具有更广泛的相关性。

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