Selective inhibition of uracil tRNA methylases of E. coli by ethionine

Abstract

L-ethionine has been found to inhibit uracil tRNA methylating enzymes in vitro under conditions where methylation of other tRNA bases is unaffected. No selective inhibitor for uracil tRNA methylases has been identified previously. 15 mM L-ethionine or 30 mM D,L-ethionine caused about 40% inhibition of tRNA methylation catalyzed by enzyme extracts from E. coli B or E. coli M3S (mixtures of methylases for uracil, guanine, cytosine, and adenine) but did not inhibit the activity of preparations from an E. coli mutant that lacks uracil tRNA methylase. Analysis of the 14CH3 bases in methyl-deficient E. coli tRNA after its in vitro methylation with E. coli B3 enzymes in the presence or absence of ethionine showed that ethionine inhibited 14CH3 transfer to uracil in tRNA, but did not diminish significantly the 14CH3 transfer to other tRNA bases. Under similar conditions 0.6 mM S-adenosylethionine and 0.2 mM ethylthioadenosine inhibited the overall tRNA base methylating activity of E. coli B preparations about 50% but neither of these ethionine metabolites preferentially inhibited uracil methylation. Ethionine was not competitive with S-adenosyl methionine. Uracil methylation was not inhibited by alanine, valine, or ethionine sulfoxide. It is suggested that the thymine deficiency that we found earlier in tRNA from ethionine-treated E. coli B cells, resulted from base specific inhibition by the amino acid, ethionine, of uracil tRNA methylation in vivo.

Small-molecule modulators of TRMT2A decrease PolyQ aggregation and PolyQ-induced cell death

“…To perform our ligand-based virtual screening, we searched for all available inhibitors of TRMT2A homologs. Unfortunately, only data for TrmA in E. coli were found 42, 43, 44, 45 . Therefore, the known TrmA inhibitors L-norleucine, L-methionine, and L-ethionine, were superimposed and a pharmacophore model was built.…”

“…The ethyl analog of L-methionine (L-ethionine) is a known non-competitive selective inhibitor. The related Sadenosyl-L-ethionine does not show such selectivity (Km = 0.6 mM in TrmA) 43 . Ethylthioadenosine, where methionine is replaced by an ethyl group shows inhibition of Km = 0.2 mM in TrmA.…”

“…Selection criteria for the pharmacophore Some of the known TrmA inhibitors are based on the methylase activity requiring the cofactor Sadenosylmethionine (SAM or AdoMet) [58]. The SAM precursor L-methionine and structurally related norleucine are weak TrmA binders [59]. In addition, the ethyl analog of L-methionine (L-ethionine) is a known non-competitive selective inhibitor [59].…”

Molecular aspects of the in vivo and in vitro effects of ethionine, an analog of methionine.

“…Ethionine does not inhibit the transport of L-methionine in E. coli (98), nor does it repress the synthesis of SAM synthetase (which methionine does) (95). However, non-methionine-specific E. coli enzymes can recognize ethionine: the D-amino acid dehydrogenase uses D-ethionine as well as D-methionine as a substrate (214), and the uracil-tRNA methyltransferase is inhibited by ethio-nine in a noncompetitive manner with respect to SAM (196).…”

“…Under these conditions, macromolecular components are unmethylated, and subsequent methylation in vivo or in vitro with radiolabeled methionine provides a method of detecting methylated cellular components and of studying the role of these postsynthetic modifications. In addition, ethionine inhibits (in a noncompetitive manner with respect to SAM) the uracil tRNA methylating enzymes from E. coli (196).…”