Abstract
Multi-aminoacyl-tRNA synthetase complex (MSC) is the second largest machinery for protein synthesis in human cells and also regulates multiple nontranslational functions through its components. Previous studies have shown that the MSC can respond to external signals by releasing its components to function outside it. The internal assembly is fundamental to MSC regulation. Here, using crystal structural analyses (at 1.88 Å resolution) along with molecular modeling, gel-filtration chromatography, and co-immunoprecipitation, we report that human lysyl-tRNA synthetase (LysRS) forms a tighter assembly with the scaffold protein aminoacyl-tRNA synthetase complex-interacting multifunctional protein 2 (AIMP2) than previously observed. We found that two AIMP2 N-terminal peptides form an antiparallel scaffold and hold two LysRS dimers through four binding motifs and additional interactions. Of note, the four catalytic subunits of LysRS in the tightly assembled complex were all accessible for tRNA recognition. We further noted that two recently reported human disease-associated mutations conflict with this tighter assembly, cause LysRS release from the MSC, and inactivate the enzyme. These findings reveal a previously unknown dimension of MSC subcomplex assembly and suggest that the retractility of this complex may be critical for its physiological functions.
Highlights
Multi-aminoacyl-tRNA synthetase complex (MSC) is the second largest machinery for protein synthesis in human cells and regulates multiple nontranslational functions through its components
Only motif 1 (MYQVKPYH) of aminoacyl-tRNA synthetase complex-interacting multifunctional protein 2 (AIMP2) interacts with lysyl-tRNA synthetase (LysRS) in the same asymmetric unit (ASU1) (Fig. 1A), and motif 2 (MYRLPNVH) extends to a nearby asymmetric unit (ASU2), where it interacts with another LysRS dimer (Fig. 1, B and C)
Following the LysRS binding sequence, AIMP2 has a leucine-zipper region at residues 48 – 81 and a GST domain at the C terminus
Summary
Data collection Space group Cell dimensions a, b, c (Å) ␣, , ␥ (°) Resolution (Å) Rsym or Rmerge (%) Mean I/(I) Completeness (%) Redundancy. The two LysRS dimers and the two copies of AIMP2 are packed with a V shape in solution (V form) (Fig. S1). In this form, each of the two LysRS dimers is connected by the N-terminal 32 residues from one AIMP2, so that two LysRS dimers do not directly contact. Two human disease-related mutations disturbed LysRS’s incorporation into MSC in cells and are conflicted with this tight assembly. This finding reveals a previously unknown dimension of MSC subcomplex assembly and suggests that the retractility of the complex may be critical for its diverse physiological functions
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