title: Induced nucleotide specificity in a GTPase.
abstract: In signal-recognition particle (SRP)-dependent protein targeting to the bacterial plasma membrane, two GTPases, Ffh (a subunit of the bacterial SRP) and FtsY (the bacterial SRP receptor), act as GTPase activating proteins for one another. The molecular mechanism of this reciprocal GTPase activation is poorly understood. In this work, we show that, unlike other GTPases, free FtsY exhibits only low preference for GTP over other nucleotides. On formation of the SRP.FtsY complex, however, the nucleotide specificity of FtsY is enhanced 10(3)-fold. Thus, interactions with SRP must induce conformational changes that directly affect the FtsY GTP-binding site: in response to SRP binding, FtsY switches from a nonspecific "open" state to a "closed" state that provides discrimination between cognate and noncognate nucleotides. We propose that this conformational change leads to more accurate positioning of the nucleotide and thus could contribute to activation of FtsY's GTPase activity by a novel mechanism.
authors.affiliation: Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143-0448, USA.
authors.forename: Shu-ou
authors.initials: SO
authors.lastname: Shan
authors.forename: Peter
authors.initials: P
authors.lastname: Walter
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D009711:Nucleotides / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012265:Ribonucleotides / Q000737:chemistry / Q000378:metabolism; D018271:Signal Recognition Particle / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C087406:FtsY protein, Bacteria; D009711:Nucleotides; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D012265:Ribonucleotides; D018271:Signal Recognition Particle; C065326:xanthosine 5'-triphosphate; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases