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

ABSTRACT: 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. The switch alters the properties of the binding pocket to allow either the accommodation of guanine or preQ(1). The peptide conformer recognising guanine, however, is also able to bind preQ(0). To investigate selectivity regulation, kinetic data for Zymomonas mobilis Tgt were recorded. They show that selectivity in favour of the actual substrate preQ(1) over preQ(0) is not achieved by a difference in affinity b

SUBMITTER: Tidten N 

PROVIDER: S-EPMC2100405 | biostudies-literature | 2007 Nov

REPOSITORIES: biostudies-literature