Crystal Structure of the Enterohemorrhagic Escherichia coli AtaT-AtaR Toxin-Antitoxin Complex

Abstract

Highlights d AtaT-AtaR is a toxin-antitoxin pair found in enterohemorrhagic E. coli d AtaT acetylates the methionyl initiator tRNA fMet and inhibits translation initiation d The AtaT-AtaR complex has the heterohexameric [AtaT-(AtaR) 4 -AtaT] structure d AtaR represses the AtaT activity by preventing AtaT from forming an active dimer

Mechanism of aminoacyl-tRNA acetylation by an aminoacyl-tRNA acetyltransferase AtaT from enterohemorrhagic E. coli

“…2b). The binding of the acceptor stem region to the interface between the AtaT dimer subunits explains the previous results showing that the AtaT homodimerization is required for both the enzymatic and toxic activities of AtaT 21 . The structure also revealed that the recognition elements in tRNAf Met for acetylation by AtaT reside in its acceptor stem region ( Fig.…”

“…f Time courses of the acetylation of Met-tRNAf Met variants with mutations in the bottom half of the three consecutive G-C pairs in a. g Quantification of the acetylation efficiencies in f, as in e. The bars in the graph are SD of three independent (n = 3) experiments, and the data are presented as mean values ± SD. respectively 20,21 . The loop between α3 and β4 in AtaTb and α1 in AtaTa form the path for the 3′-end of tRNA to enter the catalytic site and interact with the 3′-single-stranded region of tRNAf Met (Fig.…”

“…3). G108D and Y144F mutants were used as positive controls, since the mutation of G108 to D108 causes AtaT to lose its toxicity by blocking Ac-CoA binding 20,21 , and the mutation of the catalytic residue Y144 to F144 also reduces AtaT toxicity in vivo 20,21,25 . As expected, the substitution of positively charged residues in helix α1 (H34A/ R37A/R40A) attenuated the cell growth inhibition by AtaT.…”

“…Recently, the crystal structures of AtaT and its complex with the cognate antitoxin AtaR have been reported 20,21 . The structural and biochemical studies revealed that the homodimerization of AtaT is required for both the enzymatic activity and the toxicity.…”

“…The structural and biochemical studies revealed that the homodimerization of AtaT is required for both the enzymatic activity and the toxicity. The electrostatic surface potential of the dimeric AtaT showed that a positively charged patch is created upon dimer formation, implying the requirement of dimer formation for aminoacyl-tRNA binding 21 . However, the molecular mechanism for specific aminoacyl-tRNA recognition by AtaT has remained elusive.…”