Relative binding affinities of OmpR and OmpR-phosphate at the ompF and ompC regulatory sites

Charlotte G. Head, Adrienne Tardy, Linda Kenney

Research output: Contribution to journalArticle

108 Citations (Scopus)

Abstract

In Escherichia coli, porin gene expression is regulated, in part, by the two-component regulatory system consisting of the two proteins EnvZ and OmpR. EnvZ is an integral inner membrane protein that is phosphorylated by cytoplasmic ATP on a histidine residue. EnvZ modulates the activity of OmpR by phosphorylation and dephosphorylation. Phospho-OmpR (OmpR-P) binds to the porin genes ompF and ompC to regulate their expression. The simple affinity model predicts that as the concentration of OmpR-P increases, initially high-affinity binding sites on ompF are filled. Then binding sites of lower affinity on ompF and ompC are occupied and this ordered binding accounts for the differential expression of the porin genes. We demonstrate that acetyl phosphate phosphorylates OmpR at aspartate 55, the same residue phosphorylated by the kinase EnvZ. Quantification of the level of OmpR-P by HPLC and direct measurement of the binding affinities enabled us to test the affinity model. Our results indicate that phosphorylation dramatically increases the affinity of OmpR for its binding sites (greater than tenfold). We also show that the affinities of OmpR-P for F1 and C1 binding sites are not sufficiently different to provide a strong basis for discrimination. The consequences of these observations for the simple affinity model are considered.

Original languageEnglish (US)
Pages (from-to)857-870
Number of pages14
JournalJournal of Molecular Biology
Volume281
Issue number5
DOIs
StatePublished - Sep 4 1998
Externally publishedYes

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Porins
Phosphates
Binding Sites
Phosphorylation
Gene Expression
Histidine
Aspartic Acid
Membrane Proteins
Phosphotransferases
Adenosine Triphosphate
High Pressure Liquid Chromatography
Escherichia coli
Genes
Proteins

Keywords

  • Osmoregulation
  • Response regulators
  • Signal transduction
  • Transcriptional activation
  • Two-component regulatory system

ASJC Scopus subject areas

  • Molecular Biology

Cite this

Relative binding affinities of OmpR and OmpR-phosphate at the ompF and ompC regulatory sites. / Head, Charlotte G.; Tardy, Adrienne; Kenney, Linda.

In: Journal of Molecular Biology, Vol. 281, No. 5, 04.09.1998, p. 857-870.

Research output: Contribution to journalArticle

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AB - In Escherichia coli, porin gene expression is regulated, in part, by the two-component regulatory system consisting of the two proteins EnvZ and OmpR. EnvZ is an integral inner membrane protein that is phosphorylated by cytoplasmic ATP on a histidine residue. EnvZ modulates the activity of OmpR by phosphorylation and dephosphorylation. Phospho-OmpR (OmpR-P) binds to the porin genes ompF and ompC to regulate their expression. The simple affinity model predicts that as the concentration of OmpR-P increases, initially high-affinity binding sites on ompF are filled. Then binding sites of lower affinity on ompF and ompC are occupied and this ordered binding accounts for the differential expression of the porin genes. We demonstrate that acetyl phosphate phosphorylates OmpR at aspartate 55, the same residue phosphorylated by the kinase EnvZ. Quantification of the level of OmpR-P by HPLC and direct measurement of the binding affinities enabled us to test the affinity model. Our results indicate that phosphorylation dramatically increases the affinity of OmpR for its binding sites (greater than tenfold). We also show that the affinities of OmpR-P for F1 and C1 binding sites are not sufficiently different to provide a strong basis for discrimination. The consequences of these observations for the simple affinity model are considered.

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