title: Evidence for a novel GTPase priming step in the SRP protein targeting pathway.
abstract: Protein targeting by the signal recognition particle (SRP) pathway requires the interaction of two homologous GTPases that reciprocally regulate each other's GTPase activity, the SRP signal peptide- binding subunit (SRP54) and the SRP receptor alpha-subunit (SRalpha). The GTPase domain of both proteins abuts a unique 'N domain' that appears to facilitate external ligand binding. To examine the relationship between the unusual regulation and unique architecture of the SRP pathway GTPases, we mutated an invariant glycine in Escherichia coli SRP54 and SRalpha orthologs ('Ffh' and 'FtsY', respectively) that resides at the N-GTPase domain interface. A G257A mutation in Ffh produced a lethal phenotype. The mutation did not significantly affect Ffh function, but severely reduced interaction with FtsY. Likewise, mutation of FtsY Gly455 produced growth defects and inhibited interaction with Ffh. The data suggest that Ffh and FtsY interact only in a 'primed' conformation which requires interdomain communication. Based on these results, we propose that the distinctive features of the SRP pathway GTPases evolved to ensure that SRP and the SR engage external ligands before interacting with each other.
authors.affiliation: Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Building 10, Room 9D-20, Bethesda, MD 20892-1810, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: H Y
authors.initials: HY
authors.lastname: Qi
authors.forename: J B
authors.initials: JB
authors.lastname: Hyndman
authors.forename: N D
authors.initials: ND
authors.lastname: Ulbrandt
authors.forename: A
authors.initials: A
authors.lastname: Teplyakov
authors.forename: N
authors.initials: N
authors.lastname: Tomasevic
authors.forename: H D
authors.initials: HD
authors.lastname: Bernstein
mesh_terms: D000483:Alleles; D001426:Bacterial Proteins / Q000378:metabolism; D015153:Blotting, Western; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D005998:Glycine / Q000737:chemistry; D006160:Guanosine Triphosphate / Q000378:metabolism; D008024:Ligands; D008954:Models, Biological; D008958:Models, Molecular; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D018271:Signal Recognition Particle / Q000235:genetics* / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C082931:Ffh protein, E coli; C087406:FtsY protein, Bacteria; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D018271:Signal Recognition Particle; D006160:Guanosine Triphosphate; D005982:Glutathione Transferase; D020558:GTP Phosphohydrolases; D005998:Glycine