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Ratcheting Up vir Gene Expression in Agrobacterium tumefaciens : Coiled Coils in Histidine Kinase Signal Transduction
Author(s) -
Wang Yulei,
Gao Rong,
Lynn David G.
Publication year - 2002
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/1439-7633(20020402)3:4<311::aid-cbic311>3.0.co;2-n
Subject(s) - leucine zipper , coiled coil , histidine kinase , agrobacterium tumefaciens , transmembrane domain , periplasmic space , biology , transmembrane protein , transcription factor , microbiology and biotechnology , two component regulatory system , histidine , fusion protein , biochemistry , gene , amino acid , transformation (genetics) , escherichia coli , receptor , recombinant dna , mutant
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.