Glutamate versus glutamine exchange swaps substrate selectivity in tRNA-guanine transglycosylase: insight into the regulation of substrate selectivity by kinetic and crystallographic studies.

Bacterial tRNA-guanine transglycosylase (Tgt) catalyses the exchange of guanine in the wobble position of particular tRNAs by the modified base preQ(1). In vitro, however, the enzyme is also able to insert the immediate biosynthetic precursor, preQ(0), into those tRNAs. This substrate promiscuity is based on a peptide switch in the active site, gated by the general acid/base Glu235.

Crystal structures of tRNA-guanine transglycosylase (TGT) in complex with novel and potent inhibitors unravel pronounced induced-fit adaptations and suggest dimer formation upon substrate binding.

The bacterial tRNA-guanine transglycosylase (TGT) is a tRNA modifying enzyme catalyzing the exchange of guanine 34 by the modified base preQ1. The enzyme is involved in the infection pathway of Shigella, causing bacterial dysentery. As no crystal structure of the Shigella enzyme is available the homologous Zymomonas mobilis TGT was used for structure-based drug design resulting in new, potent, lin-benzoguanine-based inhibitors.

Mechanism and substrate specificity of tRNA-guanine transglycosylases (TGTs): tRNA-modifying enzymes from the three different kingdoms of life share a common catalytic mechanism.

Transfer RNA-guanine transglycosylases (TGTs) are evolutionarily ancient enzymes, present in all kingdoms of life, catalyzing guanine exchange within their cognate tRNAs by modified 7-deazaguanine bases. Although distinct bases are incorporated into tRNA at different positions in a kingdom-specific manner, the catalytic subunits of TGTs are structurally well conserved. This review provides insight into the sequential steps along the reaction pathway, substrate specificity, and conformational adaptions of the binding pockets by comparison of TGT crystal structures in complex with RNA substrates of a eubacterial and an archaebacterial species.