Chaperoning of Insertion of Membrane Proteins into Lipid Bilayers by Hemifluorinated Surfactants: Application to Diphtheria Toxin†

Hemifluorinated compounds, such as HF-TAC, make up a novel class of nondetergent surfactants designed to keep membrane proteins soluble under nondissociating conditions [Breyton, C., et al. (2004) FEBS Lett. 564, 312]. Because fluorinated and hydrogenated chains do not mix well, supramicellar concentrations of these surfactants can coexist with intact lipid vesicles. To test the ability of HF-TAC to assist proper membrane insertion of proteins, we examined its effect on the pH-triggered insertion of the diphtheria toxin T-domain. The function of the T-domain is to translocate the catalytic domain across the lipid bilayer in response to acidification of the endosome. This translocation is accompanied by the formation of a pore, which we used as a measure of activity in a vesicle leakage assay. We have also used Forster resonance energy transfer to follow the effect of HF-TAC on aggregation of aqueous and membrane-bound T-domain. Our data indicate that the pore-forming activity of the T-domain is affected b...