Molecular and General Genetics MGG

, Volume 246, Issue 6, pp 783–796 | Cite as

The osmoprotectant proline betaine is a major substrate for the binding-protein-dependent transport system ProU of Escherichia coli K-12

  • Martin Haardt
  • Bettina Kempf
  • Elke Faatz
  • Erhard Bremer
Short Communication

Abstract

The ProP and ProU transport systems of Escherichia coli mediate the uptake of several osmoprotectants including glycine betaine. Here we report that both ProP and ProU are involved in the transport of the potent osmoprotectant proline betaine. A set of isogenic E. coli strains carrying deletions in either the proP or proU loci was constructed. The growth properties of these mutants in high osmolarity minimal media containing 1 mM proline betaine demonstrated that the osmoprotective effect of this compound was dependent on either an intact ProP or ProU uptake system. Proline betaine competes with glycine betaine for binding to the proU-encoded periplasmic substrate binding protein (ProX) and we estimate a KD of 5.2 μM for proline betaine binding. This value is similar to the binding constant of the ProX protein determined previously for the binding of glycine betaine (KD of 1.4 μM). Our results thus demonstrate that the binding-protein-dependent ProU transport system of E. coli mediates the efficient uptake of the osmoprotectants glycine betaine and proline betaine.

Key words

Adaptation to high osmolarity Osmoprotectants Substrate binding protein Prop ProU 

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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • Martin Haardt
    • 1
  • Bettina Kempf
    • 1
    • 2
  • Elke Faatz
    • 1
  • Erhard Bremer
    • 1
    • 2
  1. 1.Department of BiologyUniversity of KonstanzKonstanzGermany
  2. 2.Max-Planck-Institut for Terrestrial MicrobiologyMarburgGermany

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