EcAspRS_like_N: N-terminal, anticodon recognition domain of the type found in Escherichia coli aspartyl-tRNA synthetase (AspRS), the human mitochondrial (mt) AspRS-2, the discriminating (D) Thermus thermophilus AspRS-1, and the nondiscriminating (ND) Helicobacter pylori AspRS. These homodimeric enzymes are class2b aminoacyl-tRNA synthetases (aaRSs). This domain is a beta-barrel domain (OB fold) involved in binding the tRNA anticodon stem-loop. aaRSs catalyze the specific attachment of amino acids (AAs) to their cognate tRNAs during protein biosynthesis. This 2-step reaction involves i) the activation of the AA by ATP in the presence of magnesium ions, followed by ii) the transfer of the activated AA to the terminal ribose of tRNA. In the case of the class2b aaRSs, the activated AA is attached to the 3'OH of the terminal ribose. Eukaryotes contain 2 sets of aaRSs, both of which are encoded by the nuclear genome. One set concerns with cytoplasmic synthesis, whereas the other exclusively with mitochondrial protein synthesis. Human mtAspRS participates in mitochondrial biosynthesis; this enzyme been shown to charge E.coli native tRNAsp in addition to in vitro transcribed human mitochondrial tRNAsp. T. thermophilus is rare among bacteria in having both a D_AspRS and a ND_AspRS. H.pylori ND-AspRS can charge both tRNAASp and tRNAAsn, it is fractionally more efficient at aminoacylating tRNAAsp over tRNAAsn. The H.pylori genome does not contain AsnRS.
Comment:E.coli AspRS binds yeast tRNAAsp and E. coli tRNAAsp with equal affinity. However, it only charges its cognate tRNA. The IL2 structure (E.coli AspRS bound with yeast tRNAAsp) is an inactive heterologous complex. In IL2 both tRNAs have their anticodon-stem loop bound to the N-terminal OB fold domain. However, the dimer is asymmetric with only one of two bound tRNAs entering the active site cleft of its subunit. In active homologous E. coli AspRS complexes, both tRNA molecules are bound to their respective dimeric enzyme in a symmetric manner.
Structure:1IL2, E. Coli AspRS inactive homodimer bound with yeast tRNAAsp, contacts at 3.5 A.
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