title: Leucine-regulated self-association of leucine-responsive regulatory protein (Lrp) from Escherichia coli.
abstract: Lrp is a global regulatory protein in Escherichia coli that activates expression of more than a dozen operons and represses expression of another dozen. For some operons, exogenous leucine reduces the extent of Lrp action, for others it potentiates the effect of Lrp, and for yet other operons it has no effect. In an effort to understand how leucine affects Lrp-mediated expression, we examined Lrp self-association and the effect of leucine on self-association using light scattering, chemical cross-linking, and analytical ultracentrifugation. The following results were obtained. (i) Lrp self-associates to a hexadecamer and octamer with the predominant species being hexadecamer at microM concentrations. (ii) Lrp undergoes a leucine-induced dissociation of hexadecamer to octamer. (iii) A mutant Lrp lacking 11 amino acid residues at the C terminus does not form higher-order oligomers, suggesting that the C terminus is involved in subunit association. (iv) At nM concentrations, Lrp dissociates to a dimer. It is proposed that leucine regulates the equilibrium between Lrp oligomers and thus Lrp occupancy of sites within different operons, leading to diverse regulatory patterns.
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.
authors.forename: S
authors.initials: S
authors.lastname: Chen
authors.forename: M H
authors.initials: MH
authors.lastname: Rosner
authors.forename: J M
authors.initials: JM
authors.lastname: Calvo
mesh_terms: D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003432:Cross-Linking Reagents / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D007930:Leucine / Q000378:metabolism*; D051756:Leucine-Responsive Regulatory Protein; D008027:Light; D008954:Models, Biological; D008970:Molecular Weight; D009876:Operon / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D012996:Solutions; D013816:Thermodynamics; D014157:Transcription Factors; D014461:Ultracentrifugation
chemical_list: D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C497278:Lrp protein, E coli; D012996:Solutions; D014157:Transcription Factors; D051756:Leucine-Responsive Regulatory Protein; D007930:Leucine