Caenorhabditis elegans Evolves a New Architecture for the Multi-aminoacyl-tRNA Synthetase Complex

Abstract

MARS is an evolutionary conserved supramolecular assembly of aminoacyl-tRNA synthetases found in eukaryotes. This complex was thought to be ubiquitous in the deuterostome and protostome clades of bilaterians because similar complexes were isolated from arthropods and vertebrates. However, several features of the component enzymes suggested that in the nematode Caenorhabditis elegans, a species grouped with arthropods in modern phylogeny, this complex might not exist, or should display a significantly different structural organization. C. elegans was also taken as a model system to study in a multicellular organism amenable to experimental approaches, the reason for existence of these supramolecular entities. Here, using a proteomic approach, we have characterized the components of MARS in C. elegans. We show that this organism evolved a specific structural organization of this complex, which contains several bona fide components of the MARS complexes known so far, but also displays significant variations. These data highlight molecular evolution events that took place after radiation of bilaterians. Remarkably, it shows that expansion of MARS assembly in metazoans is not linear, but is the result of additions but also of subtractions along evolution. We then undertook an experimental approach, using inactivation of the endogenous copy of methionyl-tRNA synthetase by RNAi and expression of transgenic variants, to understand the role in complex assembly and the in vivo functionality, of the eukaryotic-specific domains appended to aminoacyl-tRNA synthetases. We show that rescue of the worms and assembly of transgenic variants into MARS rest on the presence of these appended domains.Aminoacyl-tRNA synthetases are essential components of the translation machinery in all living cells. They synthesize aminoacyl-tRNA and therefore establish the genetic code by catalyzing a univocal link between an amino acid and the nucleotide triplet from the anticodon loop of the tRNA molecule (1). Despite the prevalence of this process, tRNA, aminoacyl-tRNA, and aminoacyl-tRNA synthetases are also involved in essential secondary roles (2, 3). It is therefore fundamental to understand the rules that govern their functioning in parallel pathways and to decipher the mechanisms responsible for their spatio-temporal regulation. Recent studies have suggested that the emergence of supramolecular assemblies that serve as depots for releasable regulatory proteins would be a means to control their activities in space and in time (4).A characteristic feature of aminoacyl-tRNA synthetases in animal cells is their ability to form supramolecular complexes. A multi-aminoacyl-tRNA synthetase complex (MARS) 3 containing the nine aminoacyl-tRNA synthetases ArgRS, AspRS, GlnRS, GluRS, IleRS, LeuRS, LysRS, MetRS, ProRS, and the three nonsynthetase components p18, p38, and p43 has been extensively characterized (5, 6). It is noteworthy that the complexes isolated from the arthropod Drosophila melanogaster (7), or from various vertebrates, including rat (...

Expression of Nuclear and Mitochondrial Genes Encoding ATP Synthase Is Synchronized by Disassembly of a Multisynthetase Complex

“…MSCs have been found in all eukaryotes studied so far including fungi (Simos et al, 1996), unicellular parasites (Cestari et al, 2013;van Rooyen et al, 2014), worms (Havrylenko et al, 2011), and mammals (Bandyopadhyay and Deutscher, 1971). Investigations carried out to find a functional rationale for the accretion of aaRSs and auxiliary proteins into MSCs were so far only restricted to the mammals, and although the rationale for their existence is still unclear, they seem to be dynamical edifices releasing aaRSs able to exert functions other than tRNA charging upon release.…”

A Multiple Aminoacyl-tRNA Synthetase Complex That Enhances tRNA-Aminoacylation in African Trypanosomes

“…Thus, MCP2 is a component of the T. brucei MARS complex, but unlike in C. elegans, plants, and humans, it is not found as an accessory domain of the MetRS (Fig. 7b) (10,12,65). Since MCP2 binds to other tRNAs, it may also contribute to aminoacylation by other aaRS enzymes and perhaps to tRNA recycling by recruiting and delivering tRNAs to the complex, as suggested for Arc1p (15).…”

“…For example, the MARS complex in Caenorhabditis elegans lacks the protein p43, but a p43-like domain is at the C terminus of MetRS. This sequence has a leucine zipper (LZ) domain and a tRNA-binding domain (TRBD), which interacts with the p38 ortholog and other aaRSs (12). Saccharomyces cerevisiae, on the other hand, contains an ortholog of p43, called aminoacyl-tRNA synthetase cofactor 1 protein (Arc1p).…”

Citric acid cycle and the origin of MARS

“…elegans genome harbors a horizontally acquired gene that encodes a bifunctional enzyme with isocitrate lyase and malate synthase catalytic activities, the unique enzymes of the glyoxylate shunt [30]. Interestingly, C. elegans has a multi-ARS complex with a composition different from that of the common MARS; the complex lacks AIMP3, ProRS, and AspRS, whereas ValRS is included [31]. Moreover, GluRS and ProRS are not fused and are encoded by separate genes, unlike in other bilaterians.…”