title: Evolution of function of a fused metazoan tRNA synthetase.
abstract: The origin and evolution of multidomain proteins are driven by diverse processes including fusion/fission, domain shuffling, and alternative splicing. The 20 aminoacyl-tRNA synthetases (AARS) constitute an ancient conserved family of multidomain proteins. The glutamyl-prolyl tRNA synthetase (EPRS) of bilaterian animals is unique among AARSs, containing two functional enzymes catalyzing ligation of glutamate and proline to their cognate transfer RNAs (tRNAs). The ERS and PRS catalytic domains in multiple bilaterian taxa are linked by variable number of helix-turn-helix domains referred to as WHEP-TRS domains. In addition to its canonical aminoacylation activities, human EPRS exhibits a noncanonical function as an inflammation-responsive regulator of translation. Recently, we have shown that the WHEP domains direct this auxiliary function of human EPRS by interacting with an mRNA stem-loop element (interferon-gamma-activated inhibitor of translation [GAIT] element). Here, we show that EPRS is present in the cnidarian Nematostella vectensis, which pushes the origin of the fused protein back to the cnidarian-bilaterian ancestor, 50-75 My before the origin of the Bilateria. Remarkably, the Nematostella EPRS mRNA is alternatively spliced to yield three isoforms with variable number and sequence of WHEP domains and with distinct RNA-binding activities. Whereas one isoform containing a single WHEP domain binds tRNA, a second binds both tRNA and GAIT element RNA. However, the third isoform contains two WHEP domains and like the human ortholog binds specifically to GAIT element RNA. These results suggest that alternative splicing of WHEP domains in the EPRS gene of the cnidarian-bilaterian ancestor gave rise to a novel molecular function of EPRS conserved during metazoan evolution.
authors.affiliation: Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, USA.
authors.forename: Partho Sarothi
authors.initials: PS
authors.lastname: Ray
authors.forename: James C
authors.initials: JC
authors.lastname: Sullivan
authors.forename: Jie
authors.initials: J
authors.lastname: Jia
authors.forename: John
authors.initials: J
authors.lastname: Francis
authors.forename: John R
authors.initials: JR
authors.lastname: Finnerty
authors.forename: Paul L
authors.initials: PL
authors.lastname: Fox
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D003063:Cnidaria / Q000201:enzymology* / Q000235:genetics*; D019143:Evolution, Molecular; D020440:Gene Duplication; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D020033:Protein Isoforms / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D020349:Surface Plasmon Resonance
chemical_list: D020033:Protein Isoforms; D012333:RNA, Messenger; D000604:Amino Acyl-tRNA Synthetases; C415462:glutamyl-prolyl-tRNA synthetase