A freeze-fracture study of the membrane morphology of phosphatidylethanolamine-deficient Escherichia coli cells

A freeze-fracture study of the membrane morphology of phosphatidylethanolamine-deficient... Freeze-fracture electron microscopy was applied to study membrane morphology in a phosphatidylethanolamine-deficient E. coli strain. For growth, this strain requires millimolar concentrations of specific divalent cations like Mg 2+ or Ca 2+ . These cations bring the bilayer to nonbilayer phase transition temperature of the lipids back to wild type levels by shifting the phase preference of cardiolipin in the membrane towards the inverted hexagonal (H II ) phase. Under growth conditions, these cells show a bilayer based membrane with an intramembrane particle distribution as in wild type cells. Upon lowering the temperature, smooth areas are observed corresponding to gel state lipid bilayer domains. Ca 2+ was used to manipulate the phase behavior of the membrane lipids in situ. Exposing the cells to Ca 2+ up to 100 mM at 42°C did not result in the appearance of nonbilayer structures, despite the fact that in total lipid extracts under these conditions the hexagonal H II phase was observed. However, the addition of a Ca 2+ ionophore, which leads to exposure to Ca 2+ of both faces of the plasma membrane, gives rise to formation of H II phase, stacked bilayer domains and blebbing upon addition of 50 mM CaCl 2 at 42°C. We conclude that the asymmetrical localization of divalent cations in the periplasm of this strain allows them to be functionally effective while membrane stability is maintained. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Biochimica et Biophysica Acta Biomembranes Or Bba Biomembranes Elsevier

A freeze-fracture study of the membrane morphology of phosphatidylethanolamine-deficient Escherichia coli cells

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Publisher
Elsevier
Copyright
Copyright © 1997 Elsevier Science B.V.
ISSN
0005-2736
eISSN
1879-2642
DOI
10.1016/S0005-2736(96)00232-5
Publisher site
See Article on Publisher Site

Abstract

Freeze-fracture electron microscopy was applied to study membrane morphology in a phosphatidylethanolamine-deficient E. coli strain. For growth, this strain requires millimolar concentrations of specific divalent cations like Mg 2+ or Ca 2+ . These cations bring the bilayer to nonbilayer phase transition temperature of the lipids back to wild type levels by shifting the phase preference of cardiolipin in the membrane towards the inverted hexagonal (H II ) phase. Under growth conditions, these cells show a bilayer based membrane with an intramembrane particle distribution as in wild type cells. Upon lowering the temperature, smooth areas are observed corresponding to gel state lipid bilayer domains. Ca 2+ was used to manipulate the phase behavior of the membrane lipids in situ. Exposing the cells to Ca 2+ up to 100 mM at 42°C did not result in the appearance of nonbilayer structures, despite the fact that in total lipid extracts under these conditions the hexagonal H II phase was observed. However, the addition of a Ca 2+ ionophore, which leads to exposure to Ca 2+ of both faces of the plasma membrane, gives rise to formation of H II phase, stacked bilayer domains and blebbing upon addition of 50 mM CaCl 2 at 42°C. We conclude that the asymmetrical localization of divalent cations in the periplasm of this strain allows them to be functionally effective while membrane stability is maintained.

Journal

Biochimica et Biophysica Acta Biomembranes Or Bba BiomembranesElsevier

Published: Mar 13, 1997

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