P. Neves, S.C.D.N. Lopes, I. Sousa, S. Garcia, P.
Eaton, P. Gameiro, Characterization of membrane protein reconstitution in LUVs of
different lipid composition by fluorescence anisotropy, Journal of Pharmaceutical and
Biomedical Analysis 2008, in press, doi:10.1016/j.jpba.2008.11.026
A major requirement to perform structural studies with membrane proteins is not
only to define efficient reconstitution protocols, that assure a high incorporation degree in preformed liposomes, but also a protein directionality and topology that mimics its in vivo conditions. For this kind of studies, protein reconstitution in membranes systems via a detergent-mediated pathway is usually successfully adopted, since detergents are generally used in the initial isolation and purification of membrane proteins. In this study we report the reconstitution of OmpF in preformed DMPC and E.coli liposomes using two different techniques for detergent removal: 1) exclusion chromatography and 2)
incubation with detergent-adsorbing beads. The incorporation degree was
determined by bicinchoninic acid assay and fluorescence anisotropy was used
to determine OmpF effect on the structural order of membrane lipids. These
results show that protein insertion in membranes depends both on the
technique used to remove detergent and on the lipids used to prepare the
liposomes. Furthermore, it is possible to state that although the insertion is
directly related to the size distributions of proteoliposomes, it could be efficiently recognized by steady-state fluorescence anisotropy. This technique, more popular among cell biologists, can be a very practical and straightforward
alternative to DLS to confirm membrane protein insertion.
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