Effect of temperature on the nanomechanics of lipid bilayers studied by Force Spectroscopy

¹ Universitat de Barcelona

^* To whom correspondence should be addressed. E-mail: fsanz{at}ub.edu.

Submitted on May 2, 2005
Revised on June 10, 2005
Accepted on 15 August 2005

	Abstract

The effect of temperature on the nanomechanical response of supported lipid bilayers has been studied by Force Spectroscopy with Atomic Force Microscopy. We have experimentally proved that the force needed to puncture the lipid bilayer (Fy) is temperature-dependent. The quantitative measurement of the evolution of Fy with temperature has been related to the structural changes that the surface undergoes as observed through AFM images. These studies have been carried out with three different phosphatidylcholine bilayers with different main phase transition temperature (TM), namely, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 2-dilauroyl-sn-glycero-3-phosphocholine (DLPC). The solid-like phase shows a much higher Fy than the liquid-like phase, which also exhibits a jump in the force-curve. Within the solid-like phase Fy decreases as temperature is increased, and suddenly drops as it approaches TM. Interestingly, a 'well' in the Fy vs. temperature plot occurs around TM, thus proving an 'anomalous mechanical softening' around TM. Such mechanical softening has been predicted by experimental techniques and also by MD simulations and interpreted in terms of water ordering around the phospholipid headgroups. Ion-binding has been demonstrated to increase Fy (S. Garcia-Manyes et al., Biophysical Journal, in press), and its influence on both solid and liquid phases has also been discussed.

Key Words: Atomic Force Microscopy, Force Spectroscopy, Lipid Bilayers, Nanomechanics, Phase Transitions, Temperature

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