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Differential stiffness and lipid mobility in the leaflets of purple membranes

Voïtchovsky, K.; Antoranz Contera, M.; Kamihira, M.; Watts, A.; Ryan, J.F.

Differential stiffness and lipid mobility in the leaflets of purple membranes Thumbnail


M. Antoranz Contera

M. Kamihira

A. Watts

J.F. Ryan


Purple membranes (PM) are two-dimensional crystals formed by bacteriorhodopsin and a variety of lipids. The lipid composition and density in the cytoplasmic (CP) leaflet differ from those of the extracellular (EC) leaflet. A new way of differentiating the two sides of such asymmetric membranes using the phase signal in alternate contact atomic force microscopy is presented. This method does not require molecular resolution and is applied to study the stiffness and intertrimer lipid mobility in both leaflets of the PM independently over a broad range of pH and salt concentrations. PM stiffens with increasing salt concentration according to two different regimes. At low salt concentration, the membrane Young’s normal modulus grows quickly but differentially for the EC and CP leaflets. At higher salt concentration, both leaflets behave similarly and their stiffness converges toward the native environment value. Changes in pH do not affect PM stiffness; however, the crystal assembly is less pronounced at pH ≥ 10. Lipid mobility is high in the CP leaflet, especially at low salt concentration, but negligible in the EC leaflet regardless of pH or salt concentration. An independent lipid mobility study by solid-state NMR confirms and quantifies the atomic force microscopy qualitative observations.


Voïtchovsky, K., Antoranz Contera, M., Kamihira, M., Watts, A., & Ryan, J. (2006). Differential stiffness and lipid mobility in the leaflets of purple membranes. Biophysical Journal, 90(6), 2075-2085.

Journal Article Type Article
Publication Date Mar 1, 2006
Deposit Date Oct 16, 2013
Publicly Available Date Feb 12, 2015
Journal Biophysical Journal
Print ISSN 0006-3495
Publisher Biophysical Society
Peer Reviewed Peer Reviewed
Volume 90
Issue 6
Pages 2075-2085


Accepted Journal Article (627 Kb)

Copyright Statement
NOTICE: this is the author’s version of a work that was accepted for publication in Biophysical journal. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Biophysical journal, 90/6, 2006, 10.1529/biophysj.105.072405

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