1zjw
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(New page: 200px<br /><applet load="1zjw" size="450" color="white" frame="true" align="right" spinBox="true" caption="1zjw, resolution 2.500Å" /> '''Glutaminyl-tRNA syn...)
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Revision as of 05:22, 21 November 2007
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Glutaminyl-tRNA synthetase complexed to glutamine and 2'deoxy A76 glutamine tRNA
Overview
Glutaminyl-tRNA synthetase generates Gln-tRNA(Gln) 10(7)-fold more, efficiently than Glu-tRNA(Gln) and requires tRNA to synthesize the, activated aminoacyl adenylate in the first step of the reaction. To, examine the role of tRNA in amino acid activation more closely, several, assays employing a tRNA analog in which the 2'-OH group at the 3'-terminal, A76 nucleotide is replaced with hydrogen (tRNA(2'HGln)) were developed., These experiments revealed a 10(4)-fold reduction in kcat/Km in the, presence of the analog, suggesting a direct catalytic role for tRNA in the, activation reaction. The catalytic importance of the A76 2'-OH group in, aminoacylation mirrors a similar role for this moiety that has recently, been demonstrated during peptidyl transfer on the ribosome. Unexpectedly, tracking of Gln-AMP formation utilizing an alpha-32P-labeled ATP substrate, in the presence of tRNA(2'HGln) showed that AMP accumulates 5-fold more, rapidly than Gln-AMP. A cold-trapping experiment revealed that the, nonenzymatic rate of Gln-AMP hydrolysis is too slow to account for the, rapid AMP formation; hence, the hydrolysis of Gln-AMP to form glutamine, and AMP must be directly catalyzed by the GlnRS x tRNA(2'HGln) complex., This hydrolysis of glutaminyl adenylate represents a novel reaction that, is directly analogous to the pre-transfer editing hydrolysis of noncognate, aminoacyl adenylates by editing synthetases such as isoleucyl-tRNA, synthetase. Because glutaminyl-tRNA synthetase does not possess a, spatially separate editing domain, these data demonstrate that a, pre-transfer editing-like reaction can occur within the synthetic site of, a class I tRNA synthetase.
About this Structure
1ZJW is a Single protein structure of sequence from Escherichia coli with SO4, AMP and GLN as ligands. Active as Glutamine--tRNA ligase, with EC number 6.1.1.18 Full crystallographic information is available from OCA.
Reference
tRNA-dependent aminoacyl-adenylate hydrolysis by a nonediting class I aminoacyl-tRNA synthetase., Gruic-Sovulj I, Uter N, Bullock T, Perona JJ, J Biol Chem. 2005 Jun 24;280(25):23978-86. Epub 2005 Apr 20. PMID:15845536
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