Tandem duplications of a degenerated GTP-binding domain at the origin of GTPase receptors Toc159 and thylakoidal SRP.
The evolutionary origin of some nuclear encoded proteins that translocate proteins across the chloroplast envelope remains unknown. Therefore, sequences of GTPase proteins constituting the Arabidopsis thaliana translocon at the outer membrane of chloroplast (atToc) complexes were analyzed by means of HCA. In particular, atToc159 and related proteins (atToc132, atToc120, and atToc90) do not have proven homologues of prokaryotic or eukaryotic ancestry. We established that the three domains commonly referred to as A, G, and M originate from the GTPase G domain, tandemly repeated, and probably evolving toward an unstructured conformation in the case of the A domain. It resulted from this study a putative common ancestor for these proteins and a new domain definition, in particular the splitting of A into three domains (A1, A2, and A3), has been proposed. The family of Toc159, previously containing A. thaliana and Pisum sativum, has been extended to Medicago truncatula and Populus trichocarpa and it has been revised for Oryza sativa. They have also been compared to GTPase subunits involved in the cpSRP system. A distant homology has been revealed among Toc and cpSRP GTP-hydrolyzing proteins of A. thaliana, and repetitions of a GTPase domain were also found in cpSRP protein receptors, by means of HCA analysis.
Hernández Torres
Jorge
J
Laboratorio de Biología Molecular, CINBIN, Universidad Industrial de Santander, Bucaramanga, Apartado Aéreo 678, Colombia. hernanj@uis.edu.co
Maldonado
Mónica Alexandra Arias
MA
Chomilier
Jacques
J
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics*; D020558:GTP Phosphohydrolases / Q000235:genetics*; D018745:Genome, Plant; D046913:Medicago truncatula / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics; D018532:Pisum sativum / Q000235:genetics; D032107:Populus / Q000235:genetics; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D018271:Signal Recognition Particle / Q000235:genetics*; D020524:Thylakoids / Q000378:metabolism*
D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D021122:Protein Subunits; D018271:Signal Recognition Particle; C403444:TOC159 protein, Arabidopsis; D020558:GTP Phosphohydrolases