Mutual conformational changes of tryptophanyl‐tRNA synthetase and tRNATrp in the course of their specific interaction

Abstract

TRNATrp (beef, yeast) is capable of accelerating limited tryptic hydrolysis of the N-terminal part in the polypeptide chains of dimeric beef pancreas tryptophenyl-tRNA synthetase; it can also eliminate the protective effect of tryptophanyl adenylate on the enzyme proteolysis. The effect of tRNA on the proteolysis is manifested even when the 3''-CCA terminus is removed. The conformation of the synthetase probably changes when it forms a complex with tRNATrp. Yeast tRNATrp lacking the 3''-half of the acceptor stem can still interact with the synthetase and, to a certain extent, induces changes in the conformation of the latter. The susceptibility of single-stranded and double-stranded regions of tRNATrp to cleavage with endonucleases was studied, and the results are indicative of the fact that, regardless of considerable differences in the nucleotide sequence of yeast and beef tRNATrp, their 3-dimensional structures are similar. This fact is consistent with the finding that parameters for the interaction of these tRNATrp with beef tryptophanyl-tRNA synthetase are rather close. The 3-dimensional structure of tRNATrp is altered when the enzyme forms a complex with it, as seen from a change in the circular dichroic spectrum and an elevated susceptibility of the anticodon and, apparently, acceptor stems to cleavage with nuclease. The conversion of exposed cytidine residues in tRNATrp into uridine residues results in a loss of the acceptor activity; the capability to accelerate limited tryptic hydrolysis of tryptophanyl-tRNA synthetase is also lost although the enzyme-substrate complex, as seen from circular dichroic spectra, can still be formed. The conversion of cytosine in the anticodon stem into uracil modifies the conformation of the anticodon stem. The anticodon arm (including the anticodon) and the acceptor stem play an essential role in the interaction between tRNATrp and tryptophanyl-tRNA synthetase.