Isolation and characterization of the mutant N-terminal catalytical module of the B. taurus Tyrosyl-tRNA synthetase with the replacement of Trp87 and Trp283 by alanine

Aminoacyl-tRNA synthetase is one of the major enzymes of protein synthesis. The mammalian tyrosyl-tRNA synthetase consists of two structural units, the N-terminal catalytic (mini TyrRS) and the C-terminal cytokine-like modules. In a full length TyrRS, the N-terminal module carries out the catalytic function of binding the amino acid to tRNA, while the C-module adjusts and stabilizes the placement of tRNA in the active center of the enzyme. After cleavage of tyrosyl-tRNA synthetase with elastase on the mini TyrRS and C-module, the latter exhibit cytokine properties. The aim of the work was to optimize the expression of cloned cDNA miniTyrRS Bos taurus in plasmid pET30a-39KYRS in which the tryptophan codons at position 87 and 283 are replaced with alanine codons using the site-directed mutagenesis, and to obtain the mutant one-tryptophan protein of the mini BtTyrRS for further study on using methods of fluorescence spectroscopy of conformational changes of the enzyme at the stage of tyrosyladenylate formation and in interaction with the acceptor end of tRNA Tyr , as well as determination of the effect of tryptophan residus in positions 87 and 283 in its structure on the structurally dynamic and functional properties of the enzyme. It was found that the replacement of two tryptophan codons into the alanine codons in the cDNA of the mini TyrRS cloned in the expressing plasmid pET30a-39KYRSW40 does not affect the synthesis and solubility of the mutant form of the enzyme in the strain E.coli BL21 (DE3) pLysE. The amount of soluble form of the recombinant mutant mini BtTyrRS in the cytoplasm of bacterial cells, when expressed in E. coli BL21 (DE3) pLysE strain, is significantly enhanced by incubation of bacterial culture at a temperature 25 ° C compared to a culture incubation at 37° C. The yield of the obtained purified protein of the mutant mini BtTyrRS is 2.5 mg per average from 100 ml of culture medium, which is sufficient for further structural and functional studies of the mutant form of the enzyme. The compact structure of the recombinant protein is shown by fluorescence spectroscopy.