Arnez J G, Steitz T A
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, USA.
Biochemistry. 1996 Nov 26;35(47):14725-33. doi: 10.1021/bi961532o.
Three previously described mutant Escherichia coli glutaminyl-tRNA synthetase (GlnRS) proteins that incorrectly aminoacylate the amber suppressor derived from tRNATyr (supF) with glutamine were cocrystallized with wild-type tRNAGln and their structures determined. In two of the mutant enzymes studied, Asp235, which contacts base pair G3-C70 in the acceptor stem, has been changed to asparagine in GlnRS7 and to glycine in GlnRS10. These mutations result in changed interactions between Asn235 of GlnRS7 and G3-C70 of the tRNA and an altered water structure between Gly235 of GlnRS10 and base pair G3-C70. These structures suggest how the mutant enzymes can show only small changes in their ability to aminoacylate wild-type cognate tRNA on the one hand and yet show a lack of discrimination against a noncognate U3-A70 base pair on the other. In contrast, the change of Ile129 to Thr in GlnRS15 causes virtually no change in the structure of the complex, and the explanation for its ability to misacylate supF is unclear.
三种先前描述的突变型大肠杆菌谷氨酰胺-tRNA合成酶（GlnRS）蛋白，它们错误地用谷氨酰胺对源自tRNATyr（supF）的琥珀抑制子进行氨酰化，与野生型tRNAGln共结晶并确定了其结构。在研究的两种突变酶中，在受体茎中与碱基对G3-C70接触的Asp235在GlnRS7中变为天冬酰胺，在GlnRS10中变为甘氨酸。这些突变导致GlnRS7的Asn235与tRNA的G3-C70之间的相互作用发生变化，以及GlnRS10的Gly235与碱基对G3-C70之间的水结构改变。这些结构表明，一方面突变酶在对野生型同源tRNA进行氨酰化的能力上如何仅表现出微小变化，而另一方面又对非同源的U3-A70碱基对缺乏区分能力。相比之下，GlnRS15中Ile129突变为Thr在复合物结构中几乎没有引起变化，其对supF进行错误氨酰化的能力的解释尚不清楚。
