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Biophys J. 2007 Feb 15;92(4):1233-40. Epub 2006 Dec 1.

Dual-color fluorescence-burst analysis to probe protein efflux through the mechanosensitive channel MscL.

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Biochemistry Department, Groningen Biomolecular Science and Biotechnology Institute & Materials Science Centre, University of Groningen, Groningen, The Netherlands.


The mechanosensitive channel protein of large conductance, MscL, from Escherichia coli has been implicated in protein efflux, but the passage of proteins through the channel has never been demonstrated. We used dual-color fluorescence-burst analysis to evaluate the efflux of fluorescent labeled compounds through MscL. The method correlates the fluctuations in intensity of fluorescent labeled membranes and encapsulated (macro)molecules (labeled with second fluorophore) for each liposome diffusing through the observation volume. The analysis provides quantitative information on the concentration of macromolecules inside the liposomes and the fraction of functional channel proteins. For MscL, reconstituted in large unilamellar vesicles, we show that insulin, bovine pancreas trypsin inhibitor, and other compounds smaller than 6.5 kDa can pass through MscL, whereas larger macromolecules cannot.

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