Active Site of Lysyl-tRNA Synthetase: Structural Studies of the Adenylation Reaction

Aminoacyl-tRNA synthetases play a key role in protein biosynthesis by catalyzing the specific aminoacylation of tRNA. The energy required for the formation of the ester bond between the amino acid carboxylate group and the tRNA acceptor stem is supplied by coupling the reaction to the hydrolysis of ATP. Lysyl-tRNA synthetase from Escherichia coli belongs to the family of class II synthetases and carries out a two-step reaction, in which lysine is activated by being attached to the α-phosphate of AMP before being transferred to the cognate tRNA. Crystals of the thermo-inducible E. coli lysyl-tRNA synthetase LysU which diffract to 2.1 A resolution have been used to determine crystal structures of the enzyme in the presence of lysine, the lysyl−adenylate intermediate, and the nonhydrolyzable ATP analogue AMP-PCP. Additional data have been obtained from crystals soaked in a solution containing ATP and Mn2+. The refined crystal structures give “snapshots” of the active site corresponding to key steps in the am...