Proton flux into vesicles containing Hv channels at various protein to lipid ratios.
(A) Fluorescence-based H
+ flux assay for vesicles containing a decreasing number of Hv channels. Protein to lipid ratios of 1:100 (dark blue, n = 5), 1:500 (pink, n = 2), 1:1000 (orange, n = 3), 1:5000 (yellow, n = 3), 1:10,000 (cyan, n = 4), 1:20,000 (light green, n = 3), 1:40,000 (green, n =4), 1:60,000 (violet, n = 3) and empty vesicles (red squares, n = 4) are plotted (error bars represent the standard error of the mean, range of mean for 1:500). Protein and vesicles were prepared as described in the legend.
(B) Sucrose cushion of vesicles containing Hv channels. Numbers denote the fractions collected from top to bottom. Lipid vesicles containing Hv1, with protein to lipid ratio 1: 100 (wt:wt), were layered on a sucrose gradient (From top to bottom, 140 µl sample plus 60 µl dialysis buffer, 600 µl 7 % sucrose, and 1 ml 27 % sucrose in dialysis buffer). The gradients were then centrifuged at 135,000 × g in a Sorvall RP55-S swinging
bucket rotor for 2 hours and then fractionated into 8 × 225 µl fractions. A 15 µl sample of each fraction was then mixed with 15 µl 2x running buffer and run on a 12% gel (SDS-PAGE) and stained with Coomassie blue.
(C) Determination of the fraction of functional Hv channels. Plot of μ versus the ratio of fluorescence decay contributed by Hv containing vesicles over the total fluorescence decay by addition of CCCP where μ is the ratio of the number of channels over number of vesicles calculated with
where g
Hv and g
L are the grams of Hv channel and lipid added, r is the estimated average
radius of a vesicle (100 nm), M
L is the molecular weight of the average lipid molecule (754 Da), σ is the estimated area per lipid molecule (63 Å
2 ) and M
Hv is the molecular mass of the Hv channel dimer (70,000 Da). Protein to lipid ratios are as in , 1:100 (μ = 43.0, n = 5), 1:500 (μ = 8.59, n = 2), 1:1000 (μ = 4.30, n = 3), 1:5000 (μ = 0.86, n = 3), 1:10,000 (μ = 0.43, n = 4), 1:20,000 (μ = 0.21, n = 3), 1:40,000 (μ = 0.11, n =4), 1:60,000 (μ = 0.07, n = 3) error bars represent the standard error of the mean (range of mean for 1:500). The two curves are derived from with φ (fraction of functional Hv) = 1.0, θ (fraction of reconstitution deficient vesicles) = 0.15 (red) and ϕ = 0.5, θ = 0.15 (green). The inset is a close-up view along the x-axis indicating that the fit is superior with a curve corresponding to ϕ = 1.0, θ = 0.15.