Area Deformation of Membranes from the Perspective of 2H NMR and X-ray Scattering

Abstract

We address the hypothesis that functions of cellular membranes are affected by non-specific lipid-protein interactions due to bilayer material properties that depend on both pressure and temperature [1]. Changes of either pressure or temperature cause lipid bilayer deformations that are quantified by 2H NMR and X-ray scattering for membranes under osmotic stress. We present measurements of membrane structural parameters such as bilayer thickness and the area per lipid by employing a mean-torque analysis [2-3] of 2H solid-state NMR results together with X-ray scattering data. The 2H NMR experiments for both hydration pressure (low water content) and osmotic pressure (with poly(ethyleneglycol)) show that the segmental order parameters (SCD) of DMPC approach very large values of ≈ 0.35 in the liquid-crystalline state. These two pressures are thermodynamically equivalent, because the change in chemical potential when transferring water from the interlamellar space to the bulk water phase corresponds to the induced pressure, as experimentally verified by NMR measurements [4]. By considering the equations of state at thermal equilibrium, we extend this approach to address the correspondence between osmotic pressure and hydrostatic pressure. Area per lipid measured using both NMR and X-ray measurements provides a thermodynamic parameter that quantifies membrane deformations [2]. Combined analysis of NMR and X-ray allows us to further test our understanding of dehydration and osmotic stress-induced membrane deformation. We conclude that solid-state 2H NMR spectroscopy and X-ray scattering together with bilayer membrane stress techniques are important tools for understanding of the mechanism of pressure sensitivity of membrane proteins. [1] A.V. Botelho et al. (2006) Biophys. J.91, 4464-4477. [2] H.I. Petrache et al. (2000) Biophys. J.79, 3172-3192. [3] H.I. Petrache et al. (2001) JACS 123, 12611-12622. [4] K.J. Mallikarjunaiah et al. Biophys. J.(in press).