Characterization of Small Isotropic Bicelles with Various Compositions

Abstract

Structural studies of membrane proteins are of great importance and interest, with solution and solid state NMR spectroscopy being very promising tools for that task. However, such investigations are hindered by a number of obstacles, and in the first place by the fact that membrane proteins need an adequate environment that models the cell membrane. One of the most widely used and prospective membrane mimetics is isotropic bicelles. While large anisotropic bicelles are well-studied, the field of small bicelles contains a lot of "white spots". The present work reports the radii of particles and concentration of the detergents in the monomeric state in solutions of isotropic bicelles, formed by 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC), 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate (CHAPSO), and sodium cholate, as a function of lipid/detergent ratio and temperature. These parameters were measured using (1)H NMR diffusion spectroscopy for the bicelles composed of lipids with saturated fatty chains of different length and lipids, containing unsaturated fatty acid residue. The influence of a model transmembrane protein (membrane domain of rat TrkA) on the properties of bicelles and the effect of the bicelle size and composition on the properties of the transmembrane protein were investigated with heteronuclear NMR and nuclear Overhauser effect spectroscopy. We show that isotropic bicelles that are applicable for solution NMR spectroscopy behave as predicted by the theoretical models and are likely to be bicelles rather than mixed micelles. Using the obtained data, we propose a simple approach to control the size of bicelles at low concentrations. On the basis of our results, we compared different rim-forming agents and selected CHAPS as a detergent of choice for structural studies in bicelles, if the deuteration of the detergent is not required.

NMR structure of a full‐length single‐pass membrane protein NRADD

“…In the present work, we incorporated the full‐length protein into the DMPC/CHAPS bicelles (molar ratio DMPC:CHAPS:protein equals to 100:100:1) to obtain its 3D structure and intramolecular mobility. We showed previously that the mixture of DMPC and CHAPS forms bicelles in solution . According to DSTE experiment, the diffusion coefficient of DMPC at infinite dilution is equal to 90 × 10 −12 m 2 /s at 30°C in the sample containing NRADD, which corresponds to the hydrodynamic radius of 3.08 nm, and is in close agreement with previously reported radius for DMPC/CHAPS bicelles at q = 1 …”

“…All NMR spectra were acquired on Avance III 600 and 800 MHz spectrometers (Bruker BioSpin, Germany) equipped with the triple‐resonance cryoprobes, at pH 6.2 and 40°C. Double Estimulated‐Echo pulse sequence (DSTE experiment) to measure the diffusion coefficient was performed by a procedure described in Reference . Hydrodynamic radii were calculated from the diffusion coefficients, using several corrections, to take into the account the obstruction of diffusion due to the high concentration of bicelle particles .…”

“…Double Estimulated‐Echo pulse sequence (DSTE experiment) to measure the diffusion coefficient was performed by a procedure described in Reference . Hydrodynamic radii were calculated from the diffusion coefficients, using several corrections, to take into the account the obstruction of diffusion due to the high concentration of bicelle particles . Assignment of chemical shifts was performed according to the approach described in Reference using a standard set of triple‐resonance and NOESY 3D NMR spectra.…”

“…Hydrodynamic radii were calculated from the diffusion coefficients, using several corrections, to take into the account the obstruction of diffusion due to the high concentration of bicelle particles. 8 Assignment of chemical shifts was performed according to the approach described in Reference 9 using a standard set of tripleresonance and NOESY 3D NMR spectra. BEST-TROSY 10 pulse sequences were used to obtain the triple-resonance spectra.…”

Structural and biochemical differences between the Notch and the amyloid precursor protein transmembrane domains

“…The q = 0.33 DHPC-DMPC bicelles have been extensively characterized ( 44 – 46 ), particularly with respect to the question of whether they maintain an ideal “bicelle” morphology (DHPC edge-stabilized DMPC bilayer discs) or whether, at this high DHPC content, the assemblies are better described as mixed micelles in which there is little segregation of the lipid and detergent components. Compelling recent experimental evidence favors the bilayered disc morphology ( 47 ). For the DHPC-ESM and DHPC-MSM bicelles, there is little data to support one model or the other, although the longer lipid chains of ESM and MSM relative to DMPC might be expected to confer an even higher energetic preference for formation of bilayered discs rather than mixed micelles.…”