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 Förster 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 by the dynamic interplay of two principal processes: productive pH-triggered membrane insertion and nonproductive aggregation of the aqueous T-domain at low pH. The presence of HF-TAC in the buffer is demonstrated to suppress aggregation in solution and ensure correct insertion and folding of the T-domain into the lipid vesicles, without solubilizing the latter. Thus, hemifluorinated surfactants stabilize the low-pH conformation of the T-domain as a water-soluble monomer while acting as low-molecular weight chaperones for its insertion into preformed lipid bilayers.
Palchevskyy
Sergiy S
SS
Department of Biochemistry and Molecular Biology, Kansas University Medical Center, Kansas City, Kansas 66160-7421, USA.
Posokhov
Yevgen O
YO
Olivier
Blandine
B
Popot
Jean-Luc
JL
Pucci
Bernard
B
Ladokhin
Alexey S
AS
D004167:Diphtheria Toxin / Q000737:chemistry* / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008823:Micelles; D008958:Models, Molecular; D008970:Molecular Weight; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013501:Surface-Active Agents / Q000737:chemistry* / Q000378:metabolism
D004167:Diphtheria Toxin; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008565:Membrane Proteins; D008823:Micelles; D013501:Surface-Active Agents