Lipid bicelles

Hydrophobic interactions, on the other hand, are strong, indifferent to local details, and are relatively long range. If transient direct or water-separated contacts occur between nonpolar side chains, the net effect could be local organization and an overall compaction of the polypeptide chain. Whereas the strengths of hydrophobic interactions must be considerably reduced in 8 M urea, they clearly are not eliminated, as evidenced by the persistence of lipid bicelles. Thus hydrophobic interactions probably play some role in persistent global structure, the importance of which can be tested by replacing multiple hydrophobic side chains with similarly shaped polar ones. 

Fig. 8.3 Cartoon illustrating the alignment of the particles of two different orienting media, a Disc particles represent lipid bicelles. b Rods represent viral particles. Bicelles orient with their normal orthogonal to the magnetic field and viruses with their long axis parallel to it. (Reproduced with permission from N. Tjandra, Structure 1999, 7, R205-R211.)...

Fig. 3. Schematic view of the cross-section of a micelle (a), and a detergent-lipid bicelle (b). In (b), the diameter of the bilayered region is given as 2R, while the radius of the detergent is r.

Preparing lipid/bicelle solution. Dissolve the desired lipids in an organic solvent (trifluoroethanol, TFE) together with the peptide. 

Bertelsen K, Vad B, Nielsen EH, Hansen SK, Skrydstrup T, Otzen DE, Vosegaard T, Nielsen NC (2011) Long-term-stable ether-lipid vs conventional ester-lipid bicelles in oriented solid-state NMR altered structural information in studies of antimicrobial peptides. J Phys Chem B 115 1767-1774... 

Fig. 15. Weak alignment through addition of lipid bicelles or magnetic anisotropy. The preferential orientation of the protein is depicted. The dipolar coupling is observable in this case according to the formula given in the Fig.

Measurement of Coupling Constant without (reference) and with lipid bicelles... 

Conformational dynamics are often inferred and quantified from the motional averaging of the NMR parameters. Here De Simone et al. have employed oriented solid-state NMR data, such as dipolar couplings and chemical shift anisotropy measured in lipid bicelles, to refine the conformational ensemble of these proteins in lipid membranes. They specifically investigated calcium ATPase SERCA. ... 

Fig. 5 Membrane models for NMR structure analysis, (a) An isotropic detergent micelle (left) is compared to the dimensions of lipid bilayers (right), (b) Macroscopically oriented membrane samples can be prepared on solid support, as nanodiscs, or as magnetically oriented bicelles. (c) Nomenclature and variability of liposomes small (SUV, 20-40 nm), intermediate (IUV, 40-60 nm), large (LUV, 100-400 nm), and giant unilamellar vesicles (GUV, 1 pm) multi-lamellar (MLV), oligo-lamellar (OLV) and highly heterogeneous multi-oligo-lamellar vesicles (MOLV)...

A key contribution of solid-state NMR is the ability to make detailed structural measurements of membrane proteins in their native environment, the lipid bilayer. This can make it possible to do correlated struc-ture/function studies on membrane proteins under the same sample conditions, for example, to examine the structural differences between functional states of a protein. A number of bilayer-like environments have been introduced that confer different advantages appropriate for particular membrane proteins or experiments. Three such media are discussed below as potential alternatives to reconstituting membrane proteins in proteoliposomes bicelles, nanodiscs and templating vesicles. 

Nowadays, several solution structures of membrane-bound peptides and protein fragments have been reported (33,34). More important is that bicelles have been used successfully to investigate the effect of bioactive peptides on lipid properties, such as order and dynamics, and at the same time of the dynamics of the peptides themselves (35,36). 

Preparation of DHPC stock solution. Prepare a stock solution of the detergent in water (or D20 if desired for NMR purposes). A 1M solution of DHPC is convenient for preparing bicelles with a total lipid (phospholipids + detergent) concentration of 300 mM (see Note 6). 

Bicelle preparation. Add an appropriate amount of the detergent solution to the lipid slurry to produce the desired (/-value (see Note 7). 

Preparing the bicelles. Dissolve the dry lipids in a suitable buffer (50 mM phosphate buffer) and enough stock solution of the detergent to produce the desired f/-value and total lipid concentration, as described above. 

For preparation of bicelles, it is essential that the lipids are properly suspended in buffer solution prior to the addition of the DHPC solution. If this is the case, a clear low-viscous solution is formed. 

It is convenient to use a DHPC stock solution for bicelle preparation. As DHPC is extremely hygroscopic, it is otherwise difficult to estimate the true amount of DHPC that is actually added to the lipid suspension. Furthermore, unless a stock solution is prepared, DHPC should be handled in a dry atmosphere. It is important for the estimation of bicelle size (related to the g-value) that the relative concentrations of lipids and DHPC can be controlled. 

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