Role of aspartate 143 in Escherichia coli tRNA-guanine transglycosylase: alteration of heterocyclic substrate specificity.

tRNA-guanine transglycosylase (TGT) is a key enzyme involved in the post-transcriptional modification of certain tRNAs in their anticodon wobble positions with queuine. To maintain the correct Watson-Crick base pairing properties of the wobble base (and hence proper translation of the genetic code), TGT must recognize its heterocyclic substrate with high specificity. The X-ray crystal structure of a eubacterial TGT bound to preQ1 [Romier, C.

The role of aspartic acid 143 in E. coli tRNA-guanine transglycosylase: insights from mutagenesis studies and computational modeling.

tRNA guanine transglycosylase (TGT) is a tRNA-modifying enzyme which catalyzes the posttranscriptional exchange of guanine in position 34 of tRNA(Y,H,N,D) with the modified base queuine in eukaryotes or its precursor, preQ(1) base, in eubacteria. Thus, TGT must recognize the guanine in tRNA and the free base queuine or preQ(1) to catalyze this exchange. The crystal structure of Zymomonas mobilis TGT with preQ(1) bound suggests that a key aspartate is critically involved in substrate recognition.