title: Membrane anchoring of aminoacyl-tRNA synthetases by convergent acquisition of a novel protein domain.
abstract: Four distinct aminoacyl-tRNA synthetases (aaRSs) found in some cyanobacterial species contain a novel protein domain that bears two putative transmembrane helices. This CAAD domain is present in glutamyl-, isoleucyl-, leucyl-, and valyl-tRNA synthetases, the latter of which has probably recruited the domain more than once during evolution. Deleting the CAAD domain from the valyl-tRNA synthetase of Anabaena sp. PCC 7120 did not significantly modify the catalytic properties of this enzyme, suggesting that it does not participate in its canonical tRNA-charging function. Multiple lines of evidence suggest that the function of the CAAD domain is structural, mediating the membrane anchorage of the enzyme, although membrane localization of aaRSs has not previously been described in any living organism. Synthetases containing the CAAD domain were localized in the intracytoplasmic thylakoid membranes of cyanobacteria and were largely absent from the plasma membrane. The CAAD domain was necessary and apparently sufficient for protein targeting to membranes. Moreover, localization of aaRSs in thylakoids was important under nitrogen limiting conditions. In Anabaena, a multicellular filamentous cyanobacterium often used as a model for prokaryotic cell differentiation, valyl-tRNA synthetase underwent subcellular relocation at the cell poles during heterocyst differentiation, a process also dependent on the CAAD domain.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, C.S.I.C. and Universidad de Sevilla, Avda Américo Vespucio 49, E-41092 Seville, Spain.
authors.forename: Elvira
authors.initials: E
authors.lastname: Olmedo-Verd
authors.forename: Javier
authors.initials: J
authors.lastname: Santamaría-Gómez
authors.forename: Jesús A G
authors.initials: JA
authors.lastname: Ochoa de Alda
authors.forename: Lluis
authors.initials: L
authors.lastname: Ribas de Pouplana
authors.forename: Ignacio
authors.initials: I
authors.lastname: Luque
mesh_terms: D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017033:Anabaena / Q000166:cytology / Q000201:enzymology; D002462:Cell Membrane / Q000201:enzymology* / Q000378:metabolism; D019143:Evolution, Molecular; D042541:Intracellular Space / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D014637:Valine-tRNA Ligase / Q000378:metabolism
chemical_list: D000604:Amino Acyl-tRNA Synthetases; D014637:Valine-tRNA Ligase