Solution X-ray scattering highlights discrepancies in Plasmodium multi-aminoacyl-tRNA synthetase complexes.

tRip is a tRNA import protein specific to Plasmodium, the causative agent of malaria. In addition to its membrane localization and tRNA trafficking properties, tRip has the capacity to associate with three aminoacyl-tRNA synthetases (aaRS), the glutamyl- (ERS), glutaminyl- (QRS), and methionyl- (MRS) tRNA synthetases. In eukaryotes, such multi-aaRSs complexes (MSC) regulate the moonlighting activities of aaRSs. In Plasmodium, tRip and the three aaRSs all contain an N-terminal GST-like domain involved in the assembly of two independent complexes: the Q-complex (tRip:ERS:QRS) and the M-complex (tRip:ERS:MRS) with a 2:2:2 stoichiometry and in which the association of the GST-like domains of tRip and ERS (tRip-N:ERS-N) is central. In this study, the crystal structure of the N-terminal GST-like domain of ERS was solved and made possible further investigation of the solution architecture of the Q- and M-complexes by small-angle x-ray scattering (SAXS). This strategy relied on the engineering of a tRip-N-ERS-N chimeric protein to study the structural scaffold of both Plasmodium MSCs and confirm the unique homodimerization pattern of tRip in solution. The biological impact of these structural arrangements is discussed.