title: X-ray structure of the T. aquaticus FtsY:GDP complex suggests functional roles for the C-terminal helix of the SRP GTPases.
abstract: FtsY and Ffh are structurally similar prokaryotic Signal Recognition Particle GTPases that play an essential role in the Signal Recognition Particle (SRP)-mediated cotranslational targeting of proteins to the membrane. The two GTPases assemble in a GTP-dependent manner to form a heterodimeric SRP targeting complex. We report here the 2.1 A X-ray structure of FtsY from T. aquaticus bound to GDP. The structure of the monomeric protein reveals, unexpectedly, canonical binding interactions for GDP. A comparison of the structures of the monomeric and complexed FtsY NG GTPase domain suggests that it undergoes a conformational change similar to that of Ffh NG during the assembly of the symmetric heterodimeric complex. However, in contrast to Ffh, in which the C-terminal helix shifts independently of the other subdomains, the C-terminal helix and N domain of T. aquaticus FtsY together behave as a rigid body during assembly, suggesting distinct mechanisms by which the interactions of the NG domain "module" are regulated in the context of the two SRP GTPases.
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, Illinois 60611, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Gawronski-Salerno
authors.forename: John S
authors.initials: JS
authors.lastname: Coon
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Focia
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Freymann
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018271:Signal Recognition Particle / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D040681:Structural Homology, Protein; D013824:Thermus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; C087406:FtsY protein, Bacteria; D018160:Receptors, Cytoplasmic and Nuclear; D018271:Signal Recognition Particle; D006153:Guanosine Diphosphate; D020558:GTP Phosphohydrolases