The p43 Component of the Mammalian Multi-synthetase Complex Is Likely To Be the Precursor of the Endothelial Monocyte-activating Polypeptide II Cytokine

Abstract

p43 is one of the three auxiliary components invariably associated with nine aminoacyl-tRNA synthetases as a multienzyme complex ubiquitous to all eukaryotic cells from flies to humans. The cDNA encoding the hamster protein was isolated by using mixed oligonucleotides deduced from peptide sequences. The 359-amino acid protein is the hamster homologue of the recently reported murine and human EMAP II cytokine implicated in a variety of inflammatory disorders. The sequence of several proEMAP II proteins suggests that the p43 component of the complex is the precursor of the active mature cytokine after cleavage at a conserved Asp residue. The COOH-terminal moiety of p43 is also homologous to polypeptide domains found in bacterial methionyl-or phenylalanyl-tRNA synthetases and in the yeast Arc1p/G4p1 protein that associates with yeast methionyl-tRNA synthetase. Our results implicate the COOH-terminal moiety of p43 as a RNA binding domain. In the native state, as a component of the multisynthetase complex, p43 may be required for tRNA channeling and, after proteolytic processing occurring in tumor cells, would acquire inflammatory properties possibly related to apoptosis. The release of a truncated p43 from the complex could be involved in mediation of the signaling of tumor cells and stimulation of an acute inflammatory response.Aminoacyl-tRNA synthetases catalyze the activation of their cognate amino acid and transfer to the relevant tRNA. In mammals, this family of enzyme contributes two distinct high molecular mass structures: a complex made of nine synthetases and a complex involving valyl-tRNA synthetase and the ␣, ␤, ␥, and ␦ subunits of elongation factor 1. The ten other aminoacyltRNA synthetases are generally described as free enzymes (1-3). The multisynthetase complex contains the nine aminoacyl-tRNA synthetase activities for amino acids Glu, Pro, Ile, Leu, Met, Gln, Lys, Arg, and Asp and the three auxiliary proteins with masses of 18, 38, and 43 kDa. It is ubiquitous to all coelomate metazoan species from arthropods to humans (4). Immunoprecipitation experiments demonstrated the tight association of all of these components (5-7). Electron microscopy studies showed a fairly elongated U-shaped structure (8). Although the three nonsynthetase components were invariably encountered in this complex, their structural or functional role within this multi-subunit structure was not established.We have recently reported the cloning of the cDNA encoding the p18 component of the complex (9). It shares sequence homology with a protein domain recovered in the NH 2 -terminal polypeptide extension of human valyl-tRNA synthetase and in the NH 2 -terminal domains of the ␤ and ␥ subunits of elongation factor 1. In the valyl-tRNA synthetase⅐EF-1H complex, this domain has been involved in protein-protein interaction between the ␤ and ␥ subunits of the eukaryotic elongation factor EF-1H (10) or between valyl-tRNA synthetase and EF-1H (11). This led us to suggest that p18 is involved in anchoring the multisynthetase complex to th...

A Three-dimensional Working Model of the Multienzyme Complex of Aminoacyl-tRNA Synthetases Based on Electron Microscopic Placements of tRNA and Proteins

“…The C-terminal domain of p43 is a general tRNA binding domain (7). This suggests that reasonable conclusions about the correspondence of the areas of gold labeling to positions of p43 could be aided by consideration of sites of tRNA binding to the multisynthetase complex as well as results from previous studies.…”

“…This serves as a nonspecific RNA binding domain (29,32), which may function in trans to recruit tRNAs for specific enzyme(s) within the multisynthetase complex. This would result in enhancement of catalytic efficiencies (7,33). Such an effect on aminoacylation has been observed in yeast with the p43 homolog Arc1p, which forms a ternary complex with MetRS and GluRS (34,35).…”

“…The supporting data were from cross-linking reactions (14) as well as genetic two-hybrid studies (7,16). Spot 3 is on the midline of the vertical axis of the particle.…”

“…The first of these, p18, has been shown to interact with EF-1␥, which may facilitate transfer of aminoacyl-tRNAs to the ribosome (6). Data from yeast two-hybrid screens (7), in vitro binding assays (8), and deletion analysis (9) indicate that p38 functions as a scaffolding protein and appears to be essential for complex assembly. Of particular interest is protein p43, which also appears to have multiple functions.…”

Missense variants in AIMP1 gene are implicated in autosomal recessive intellectual disability without neurodegeneration

“…[1][2][3] The tRNA-binding domain associates with several aminoacyl-tRNA synthetases. On cleavage from the p43 component of the MSC, this domain becomes an independent domain with inflammatory cytokine activity.…”