X-ray Diffraction Study of the Effect of the Detergent Octyl Glucoside on the Structure of Lamellar and Nonlamellar Lipid/Water Phases of Use for Membrane Protein Reconstitution

Abstract

The phase behavior and structural parameters of dioleoylphosphatidylethanolamine (DOPE), monoolein (MO), and dipalmitoylphosphatidylcholine (DPPC) hydrated in excess aqueous phase containing micellar octyl glucoside (OG) were investigated by means of synchrotron X-ray diffraction in a wide range of temperatures. The lipid-to-detergent molar ratios were selected to be equal to those in a recent membraneprotein-reconstitution study. It was established that lipids displaying either nonlamellar (DOPE and MO) or lamellar propensities (DPPC) form mixed supramolecular structures with the detergent OG. The phase states and structures of these mixed assemblies are essentially different from those of the pure lipid components. At full hydration and at the investigated lipid-to-detergent molar ratios, OG destabilizes the inverted-hexagonal (HII) phase organization of DOPE and the inverted cubic (Q 224 ) structure of MO, transforming them into a lamellar liquid crystalline (LR) phase. The fluid DOPE/OG and MO/OG bilayers totally accommodate the micellar OG from the aqueous phase, as evidenced by the absence of diffuse scattering of OG or lipid/OG micelles. In the temperature interval from 0 to 52 °C, the investigated DOPE/ OG/water and MO/OG/water systems are in the lamellar LR state and do not undergo structural phase transitions. The DPPC/OG/water system undergoes a phase transition from a gel to a liquid-crystalline phase state. Due to the particular molar amount of OG in this system, a coexistence of mixed DPPC/OG bilayers and DPPC/OG micelles was found. The structural results suggest that the DOPE/OG and MO/OG systems, which are of lamellar rather than of nonlamellar organizations, are suitable for reconstitution of membrane proteins, as was established for DPPC/OG membranes.

Self-Assembled Multicompartment Liquid Crystalline Lipid Carriers for Protein, Peptide, and Nucleic Acid Drug Delivery

“…Tuning of the aqueous nanochannel sizes ( Figure 4) constitutes a means for control of their encapsulation capacity for biomolecules. In order to get insight into the mechanism of nanoconfinement of protein, peptides, or DNA in labyrinthine cubic network structures, [10][11][12][13][14][15][45][46][47][48][49][50][57][58][59] we discuss the monoolein cubic phase swelling as related to the changes in the lipid membrane curvature. The spontaneous monolayer curvature of the monoglyceride lipid assemblies is negative.…”

“…12,46,47,66 The monolayer curvature is reduced upon accommodation of such surfactant molecules at the apolar/polar interface and the aqueous nanochannels are enlarged ( Figure 4B). This corresponds to a cubic phase swelling and a structural change to a less curved structure with larger water channels 46 (D w ≈ 7 nm).…”

“…The bicontinuous Pn3m cubic phase tolerates high concentrations of nonionic detergents before a phase transformation to a lamellar phase occurring at elevated surfactant content. 12,47 Beyond the maximal hydration level (D Large phase) that can be attained with a diamond-type cubic phase with large water channels 46 upon augmenting the interfacial curvature modulator concentration, [68][69][70] the swelling can proceed through a phase transition to sponge phases. 70 The latter are lacking long-range order and their aqueous cave compartments could be up to three times larger than the nanochannels in a normal bicontinuous cubic phase.…”

A review of factors affecting the success of membrane protein crystallization using bicelles

“…As OG is added to cubic MO (Qiu, 2000), the OG incorporates homogenously within the membrane moving the structure from a continuous packing of membranous blocks to a lamellar stacking of fluid membranous sheets. Similarly, when OG was added to a lamellar phase formed by DPPC, it also changed the phase from the viscoelastic gel to a fluid Lα lamellar phase generally only seen by DPPC at temperatures above its melting point (60). Other reports have showed that lamellar liposomes created from egg phosphatidyl choline and egg phosphatidic acid become solubilized by less than 10 mg/ml DM in solution (61; 62) and POPC vesicles were solubilized with alkyl ether with similar characteristics as decylmaltoside, where an increase in detergent composition moves the solution from a lamellar phase to a mixed micelle cubic phase (63; 64).…”

“…The addition of OG to DPPC and DOPE bilayers lead to a decrease in d-spacing, however detergents such as dodecyl sulfate are expected to increase the lamellar spacing (60; 68). OG decreases the inter-lamellar spacing of DOPE bilayers with increasing temperature, while increasing DPPC inter-lamellar spacing (60). DM had little effect, while dodecyl-β-d-glucopyranoside (DG) increased the spacing of DPPC lamellar structures at room temperature.…”