Open AccessStructure of the prolyl‐tRNA synthetase from the eukaryotic pathogen Giardia lamblia
Author(s) -
Larson Eric T.,
Kim Jessica E.,
Napuli Alberto J.,
Verlinde Christophe L. M. J.,
Fan Erkang,
Zucker Frank H.,
Van Voorhis Wesley C.,
Buckner Frederick S.,
Hol Wim G. J.,
Merritt Ethan A.
Publication year - 2012
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444912024699
Subject(s) - giardia lamblia , biology , biochemistry , transfer rna , aminoacyl trna synthetase , cysteine , amino acid , amino acyl trna synthetases , enzyme , gene product , eukaryote , gene , genetics , rna , genome , gene expression
The genome of the human intestinal parasite Giardia lamblia contains only a single aminoacyl‐tRNA synthetase gene for each amino acid. The Giardia prolyl‐tRNA synthetase gene product was originally misidentified as a dual‐specificity Pro/Cys enzyme, in part owing to its unexpectedly high off‐target activation of cysteine, but is now believed to be a normal representative of the class of archaeal/eukaryotic prolyl‐tRNA synthetases. The 2.2 Å resolution crystal structure of the G. lamblia enzyme presented here is thus the first structure determination of a prolyl‐tRNA synthetase from a eukaryote. The relative occupancies of substrate (proline) and product (prolyl‐AMP) in the active site are consistent with half‐of‐the‐sites reactivity, as is the observed biphasic thermal denaturation curve for the protein in the presence of proline and MgATP. However, no corresponding induced asymmetry is evident in the structure of the protein. No thermal stabilization is observed in the presence of cysteine and ATP. The implied low affinity for the off‐target activation product cysteinyl‐AMP suggests that translational fidelity in Giardia is aided by the rapid release of misactivated cysteine.