The Spectroscopic Study of E. coli Arginyl-tRNA Synthetase (ArgRS) and its Mutants

The conformation of native enzyme ArgRS and its mutants ArgRS306KA, ArgRS306KR and ArgRS381KA was studied by absorbance spectrum, Difference spectrum with solvent perturbation, fluorescence spectrum and CD spectrum. The results showed that the chromophores of ArgRS306KR and ArgRS306KA had shifted to different micro environments in comparison to the native enzyme. Compared to the native enzyme, ArgRS306KA had and even bigger conformational change than ArgRS306KR, while the conformation difference between ArgRS381KA and ArgRS was not big enough to be perceivable in the spectrum. The analysis of CD spectrum showed the less the percentage of beta-turn in the ArgRS mutants, the lower the activity of the mutants. The conclusion can be drawn that the positive charge of Lys306 is very important to maintain the conformation of ArgRS, the change of conformation might be mainly responsible for the loss of enzyme of the mutants, while the substitution of Lys381 seems to cause no perceivable change of the enzyme conformation.