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Translational Diffusion and Interaction of a Photoreceptor and Its Cognate Transducer Observed in Giant Unilamellar Vesicles by Using Dual‐Focus FCS
Author(s) -
Kriegsmann Jana,
Gregor Ingo,
von der Hocht Iris,
Klare Johann,
Engelhard Martin,
Enderlein Jörg,
Fitter Jörg
Publication year - 2009
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200900251
Subject(s) - vesicle , biophysics , fluorescence correlation spectroscopy , transmembrane protein , diffusion , lipid bilayer , membrane , chemistry , intermolecular force , molecule , membrane protein , radius , crystallography , biochemistry , biology , physics , receptor , organic chemistry , thermodynamics , computer security , computer science
Abstract In order to monitor membrane–protein binding in lipid bilayers at physiological protein concentrations, we employed the recently developed dual‐focus fluorescence correlation spectroscopy (2fFCS) technique. In a case study on a photoreceptor consisting of seven transmembrane helices and its cognate transducer (two transmembrane helices), the lateral diffusion for these integral membrane proteins was analyzed in giant unilamellar vesicles (GUVs). The two‐dimensional diffusion coefficients of both separately diffusing proteins differ significantly, with D =2.2×10 −8 cm 2 s −1 for the photoreceptor and with D =4.1×10 −8 cm 2 s −1 for the transducer. In GUVs with both membrane proteins present together, we observed significantly smaller diffusion coefficients for labelled transducer molecules; this indicates the presence of larger diffusing units and therefore intermolecular protein binding. Based on the phenomenological dependence of diffusion coefficients on the molecule's cylindrical radius, we are able to estimate the degree of membrane protein binding on a quantitative level.