title: Ratcheting up vir gene expression in Agrobacterium tumefaciens: coiled coils in histidine kinase signal transduction.
abstract: The transmembrane histidine kinase VirA is responsible for the recognition of information from several plant-derived xenognostic signals that control gene transfer between Agrobacterium tumefaciens and its eukaryotic host. As with other histidine autokinases, VirA appears to exist as a homodimer within the inner membrane of the bacterium. In this study, we identify the putative homodimeric coiled-coil-like motifs Helix TM2 (amino acids (aa) 259-288) and Helix C (aa 293-327) within the previously assigned signal input domain. The functional importance of these coiled-coil interactions in signal-mediated VirA activation is investigated by the construction of fusion proteins with the leucine zipper domain of the transcription factor GCN4. Replacement of the membrane-spanning and periplasmic domains of VirA with the GCN4 leucine zipper gave functional proteins with increased signal-induced vir gene expression. When the GCN4 fusion was used to conformationally bias the interface of the Helix C coiled coil, constitutively active chimeras were created. The activity of these constructs was dependent on the interface of the Helix C coiled coil, and a ratchet model is proposed in which VirA activation is achieved by signal-induced switching of the interfaces of the homodimer. Since VirA functions as a transducer and integrates various host cues indirectly, these data highlight its role as an "antenna" for the tumor-inducing (Ti) plasmid, able to monitor the host proteome so as to select for successful xenognostic signaling strategies.
authors.affiliation: Department of Chemistry, University of Chicago, 5735 S. Ellis Avenue, Chicago, IL 60637, USA.
authors.forename: Yulei
authors.initials: Y
authors.lastname: Wang
authors.forename: Rong
authors.initials: R
authors.lastname: Gao
authors.forename: David G
authors.initials: DG
authors.lastname: Lynn
mesh_terms: D016960:Agrobacterium tumefaciens / Q000201:enzymology / Q000235:genetics*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins; D004789:Enzyme Activation / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D000071677:Histidine Kinase; D008969:Molecular Sequence Data; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D016415:Sequence Alignment; D015398:Signal Transduction / Q000235:genetics*; D015854:Up-Regulation; D037521:Virulence Factors
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D037521:Virulence Factors; D011494:Protein Kinases; D000071677:Histidine Kinase