Removal of arginyl‐tRNA synthetase markedly alters the three‐dimensional structure of the eukaryotic multisynthetase complex

Abstract

A high molecular mass assembly of nine aminoacyl-tRNA synthetase activities and three auxiliary proteins is characteristic of multicellular eukaryotes. The likely biological significance is organization of protein biosynthesis machinery and/or regulation of participation in non-canonical functions. Through use of labeled proteins and tRNAs as reporter molecules, recent progress has been made toward determining placement of multisynthetase complex constituents in a three-dimensional context [CL Wolfe et al. (2005) J. Biol. Chem. 280:38870]. This study assesses structural effects of removal of arginyl-tRNA synthetase by incubation with 0.75 M LiCl [MT Norcum (1991) J. Biol. Chem. 264:15398]. Calculation of three-dimensional structures from electron microscopic images of samples negatively stained with methylamine vanadate shows marked changes compared with control. As oriented by the three-domain model, a prominent protrusion at the interface of domain I and II is missing. Mass is also reduced across the connecting portions of these domains on the side of the particle that contains the carboxyl termini of auxiliary protein p43 (AIMP-1). The structure also partially collapses. That is, the characteristic internal cleft is much narrower than control and the upper “arms” are closer together. Thus, in the three-dimensional context of the three-domain model of the multisynthetase complex, the arginyl-tRNA synthetase dimer bridges two domains and stabilizes the overall ultrastructure. This work was supported by National Science Foundation grants MCB-0090539 and MCB-0215940.