Crystal Structures of Trypanosomal Histidyl-tRNA Synthetase Illuminate Differences between Eukaryotic and Prokaryotic Homologs

Abstract

Crystal structures of histidyl-tRNA synthetase from the eukaryotic parasites Trypanosoma brucei and Trypanosoma cruzi provide a first structural view of a eukaryotic form of this enzyme, and reveal differences from bacterial homologs. Histidyl-tRNA synthetases in general contain an extra domain inserted between conserved motifs 2 and 3 of the Class II aminoacyl-tRNA synthetase catalytic core. The current structures show that the three dimensional topology of this domain is very different in bacterial and archaeal/eukaryotic forms of the enzyme. Comparison of apo and histidine-bound trypanosomal structures indicates substantial active site rearrangement upon histidine binding, but relatively little subsequent rearrangement after reaction of histidine with ATP to form the enzyme's first reaction product, histidyladenylate. The specific residues involved in forming the binding pocket for the adenine moiety differ substantially both from the previously characterized binding site in bacterial structures and from the homologous residues in human histidyl-tRNA synthetases. The essentiality of the single histidyl-tRNA synthetase gene in T. brucei is shown by a severe depression of parasite growth rate that results from even partial suppression of expression by RNA interference.

Genetic Validation of Aminoacyl-tRNA Synthetases as Drug Targets in Trypanosoma brucei

“…Several groups have also reported the identification of MetRS, IleRS, and LeuRS inhibitors with antitrypanosome activity (30)(31)(32)(33)(34)(35). Crystal structures have been solved for many of the aaRSs across several species (15), including the structures of HisRS (36) and TrpRS (37) from T. brucei, which will aid in understanding how to target these enzymes for HAT drug discovery. Finally, we recently showed that a number of aaRSs from T. brucei associate into a MARS complex (21).…”

The Potential of Secondary Metabolites from Plants as Drugs or Leads against Protozoan Neglected Diseases—Part III: In-Silico Molecular Docking Investigations

“…Histidyl-tRNA synthetase (HisRS) 3HRI [140] 3HRK, 3LC0 [140] Histo-aspartic protease (HAP) 3FNS, 3FNT, 3FNU [141] β-Hydroxyacyl-acyl carrier protein Dehydratase (FabZ) 3AZ8, 3AZ9, 3AZA, 3AZB [142] (E)-4-hydroxy-3-methyl-but-2-enyl-diphosphate reductase (LytB)…”

Highlights on Trypanosomatid Aminoacyl-tRNA Synthesis

“…Furthermore, in many eukaryotes, the HisRS contains one or more copies of a short, N-terminal domain named WHEP. The WHEP domains are present in several non-homologous aaRSs and mediate different biological activities not related to aminoacyl-tRNA synthesis (Freist et al 1999 ;Merritt et al 2010 ).…”

“…The sequence identity between both trypanosomal HisRS and previously studied bacterial homologs is on the order of 25 % in the catalytic domain and lower elsewhere. When compared to both human HisRS sequences (HARS1 and HARS2), trypanosomal enzymes present an identity of less than 30 % (Merritt et al 2010 ).…”

“…The human N-terminal WHEP domain has been shown to be essential for its activity and the trypanosomal enzymes studied were truncations of this domain, that although were tested for their ability to activate histidine, were not tried in an aminoacylation reaction. In order to see if there was an equivalent of the WHEP domain in these kinetoplastida enzymes ( L. major included), the authors used two different secondary-structure predictors that show they have a strong propensity for helix formation around residues 5-28, although it does not predict a second helical region that would pair with the fi rst to form a WHEP-like 2-helix bundle (Merritt et al 2010 ).…”