Tyr‐426 of the Escherichia coli asparaginyl‐tRNA synthetase, an amino acid in a C‐terminal concerved motif, is involved in ATP binding

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Abstract
Sequence comparisons of the E. Coli asparaginyl-tRNA synthetase (NRSEC) with aminoacyl-tRNA synthetase sequences of class II enzymes show significant homologies with aspartyl- and lysyl-tRNA synthetases. Three conserved regions were found, one of which is located in the C-terminal part of the NRSEC sequence. Site-directed mutagenesis was performed in this conserved region. A single point mutation Tyr-426→Ser results in a 15-fold increase in the K m for ATP, while all the other kinetic parameters remain unchanged. The replacement of this Tyr-426 by a Phe does not affect the behavior of the enzyme. These data indicate that Tyr-426 is part of the ATP binding site.