Membrane mimetic systems, solution

While micelles and bicelles have served as the membrane-mimetic solvent for the majority of solution NMR studies on integral membrane proteins, the identification of suitable NMR-compatible solvents remains a formidable challenge. With <30 unique multi-spanning membrane protein structures determined by solution NMR, there is a clear need to expand the current library of solubilization agents for this purpose. In response to this problem, creative approaches are currently being developed that may open the door to solution NMR for a wider range of membrane proteins in the future. Some of the systems that have started to yield promising results include nanodiscs, amphipols, and reverse micelles. 

The membrane mimetic fructose dehydrogenase system for fructose sensing described in this paper is stable for at least several days. Activity loss appears to occur primarily due to desorption of Qa from the electrode surface since much electrode activity could be restored by exposure of the electrode to a solution containing an alternate lipophilic mediator, decylubiquinone. Efforts are underway to improve mediator retention with the hope that electrode stability can be increased further to a practical level. 

FIGURE 10 Distribution of a representative micelle population as a function of aggregation number /. The dashed curve indicates the redistribution after a small perturbation of the system that leads to dissociation and decrease of the mean aggregation number of micelles. The dotted line is the final equilibrium distribution, and 2 are the characteristic relaxation times of the process indicated by the arrows. [From Schelly, Z. A. etal. (1979). In Solution Chemistry of Surfactants, pp. 323-325. Plenum, New York, as discussed in Fendler, J. H. (1982). Membrane Mimetic Chemistry, Wiley, New York.]... 

Micelles (SDS is often used) and bicelles (made of long and short chain phosphatidylcholines) tumble isotropically in solution and can accommodate peptides and proteins (Figure 1) to provide better mimet-ics for membrane proteins and peptides than organic solvents, which themselves can induce secondary structures in peptides and proteins. Indeed, good protein function and high resolution NMR spectra can be obtained from micellar-protein complexes, with sufficient resolution to permit structural analysis. Bicelles align in the applied field with the membrane normal perpendicular to the applied field, and by doping the system with lanthanides (Tm, Yb, Er or... 

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