Evidence for unbenignant nature of glucose as a replacement for water in purple membranes

Gibson, Nicholas J.; Cassim, Joseph Y.

doi:10.1016/s0006-3495(93)81510-8

Biophysical Journal

1993

DOI: 10.1016/s0006-3495(93)81510-8

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Evidence for unbenignant nature of glucose as a replacement for water in purple membranes

Nicholas J. Gibson

Joseph Y. Cassim

Abstract: The net angle (theta(alpha)) between the seven helical segments of the bacteriorhodopsin (bR) polypeptide and the normal to the membrane plane of the purple membrane (PM) is approximately 0 degrees when determined by oriented far-ultraviolet (UV) circular dichroism (OCD) and midinfrared linear dichroism (IRLD). However, theta(alpha) is approximately 11 degrees when determined by high-resolution electron cryo-microscopy and electron diffraction (EMD). The spectral studies are made with fresh hydrated PM films a… Show more

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Cited by 2 publications

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“…These new findings reveal that material properties of the lipid bilayer ( 3 , 4 , 25 ) are important in modulating the conformational energetics of integral membrane proteins such as rhodopsin. Several preliminary reports of this research have appeared ( , ).…”

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Conformational Energetics of Rhodopsin Modulated by Nonlamellar-Forming Lipids

et al. 2002

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Rhodopsin is an important example of a G protein-coupled receptor (GPCR) in which 11-cis-retinal is the ligand and acts as an inverse agonist. Photolysis of rhodopsin leads to formation of the activated meta II state from its precursor meta I. Various mechanisms have been proposed to explain how the membrane composition affects the meta I-meta II conformational equilibrium in the visual process. For rod disk membranes and recombinant membranes containing rhodopsin, the lipid properties have been discussed in terms of elastic deformation of the bilayer. Here we have investigated the relation of nonlamellar-forming lipids, such as dioleoylphosphatidylethanolamine (DOPE), together with dioleoylphosphatidylcholine (DOPC), to the photochemistry of membrane-bound rhodopsin. We conducted flash photolysis experiments for bovine rhodopsin recombined with DOPE/DOPC mixtures (0:100 to 75:25) as a function of pH to explore the dependence of the photochemical activity on the monolayer curvature free energy of the membrane. It is well-known that DOPC forms bilayers, whereas DOPE has a propensity to adopt the nonlamellar, reverse hexagonal (H(II)) phase. In the case of neutral DOPE/DOPC recombinants, calculations of the membrane surface pH confirmed that an increase in DOPE favored the meta II state. Moreover, doubling the PE headgroup content versus the native rod membranes substituted for the polyunsaturated, docosahexaenoic acyl chains (22:6 omega 3), suggesting rhodopsin function is associated with a balance of forces within the bilayer. The data are interpreted by applying a flexible surface model, in which the meta II state is stabilized by lipids tending to form the H(II) phase, with a negative spontaneous curvature. A simple theory, based on principles of surface chemistry, for coupling the energetics of membrane proteins to material properties of the bilayer lipids is described. For rhodopsin, the free energy balance of the receptor and the lipids is altered by photoisomerization of retinal and involves curvature stress/strain of the membrane (frustration). A new biophysical principle is introduced: matching of the spontaneous curvature of the lipid bilayer to the mean curvature of the lipid/water interface adjacent to the protein, which balances the lipid/protein solvation energy. In this manner, the thermodynamic driving force for the meta I-meta II conformational change of rhodopsin is tightly controlled by mixtures of nonlamellar-forming lipids having distinctive material properties.

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Conformational Energetics of Rhodopsin Modulated by Nonlamellar-Forming Lipids

et al. 2002

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Determination of the amount of native structural bacteriorhodopsin in purple membrane Langmuir-Blodgett films by a spectroscopic surface denaturation quantifying technique

Sugiyama

Ikematsu

Iseki

et al. 1997

Biochimica et Biophysica Acta (BBA) - Biomembranes

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Purple membrane (PM) shows denaturation when spread over an air/water interface. We established a technique, which we call the spectroscopic surface denaturation quantifying (SSDQ) technique, that uses infrared linear dichroism to determine the amount of native structural bacteriorhodopsin (BR) in PM Langmuir-Blodgett (LB) films. Using the SSDQ technique we found that the conformational change after surface denaturation of BR was the same as that caused by ethanol treatment. By extrapolating the data of the amount of non-denatured BR molecules in PM LB films vs. the area of a single BR molecule on an air/water interface, we also found that the surface area of a single non-denatured BR molecule was 11.5 nm2, which is consistent with that determined by high-resolution electron cryo-microscopy and electron diffraction (EMD). These results demonstrate that the SSDQ technique is effective in quantifying the amount of native structural BR in PM LB films. The SSDQ technique is also applicable to other types of protein consisting of alpha-helical conformation.

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Evidence for unbenignant nature of glucose as a replacement for water in purple membranes

Cited by 2 publications

References 43 publications

Conformational Energetics of Rhodopsin Modulated by Nonlamellar-Forming Lipids

Conformational Energetics of Rhodopsin Modulated by Nonlamellar-Forming Lipids

Determination of the amount of native structural bacteriorhodopsin in purple membrane Langmuir-Blodgett films by a spectroscopic surface denaturation quantifying technique

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