Quorum-sensing signal binding results in dimerization of TraR and its release from membranes into the cytoplasm.
Promoter binding by TraR and LuxR, the activators of two bacterial quorum-sensing systems, requires their cognate acyl-homoserine lactone (acyl-HSL) signals, but the role the signal plays in activating these transcription factors is not known. Soluble active TraR, when purified from cells grown with the acyl-HSL, contained bound signal and was solely in dimer form. However, genetic and cross-linking studies showed that TraR is almost exclusively in monomer form in cells grown without signal. Adding signal resulted in dimerization of the protein in a concentration-dependent manner. In the absence of signal, monomer TraR localized to the inner membrane while growth with the acyl-HSL resulted in the appearance of dimer TraR in the cytoplasmic compartment. Affinity chromatography indicated that the N-terminus of TraR from cells grown without signal is hidden. Analysis of heterodimers formed between TraR and its deletion mutants localized the dimerization domain to a region between residues 49 and 156. We conclude that binding signal drives dimerization of TraR and its release from membranes into the cytoplasm.
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Department of Crop Sciences, 1201 West Gregory Drive, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Luo
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Smyth
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Gao
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Beck von Bodman
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Farrand
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D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000378:metabolism; D000215:Acylation; D016960:Agrobacterium tumefaciens / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D015153:Blotting, Western; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*
D001426:Bacterial Proteins; D008565:Membrane Proteins; D012097:Repressor Proteins; C080512:TraR protein, Agrobacterium tumefaciens; D015534:Trans-Activators; C064778:LuxR autoinducer binding proteins; C088386:homoserine lactone; D015107:4-Butyrolactone