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Figure 3
(a) Radially averaged scattering intensities of MTs and MT–lipid complexes (solid symbols), using DOTAP/DOPC solutions with xCL = NCL/(NCL + NNL) as indicated in the figure. RCL/T = NCL/NT is given by RCL/T = 160xCL, corresponding to the point at which the total amount of lipid is exactly enough to coat each MT with a bilayer. For xCL = 0.1 two scans are shown, 2 h and 60 h after preparing the sample. The broken curves are examples of the assumed background (Andreu et al., 1992BB1; Fernando-Diaz et al., 1996BB3; Needleman et al., 2004bBB12). (b) Scattering data from (a), following background subtraction (open symbols). The solid curves are the fitted scattering models. Their χ2 values are as in the figure. (c) The variation of the radial electron density, Δρ(r), relative to water (broken lines), of the MTs and complex walls, obtained from fitting the scattering data in (b) to models of concentric cylinders. r is the distance from the center of the cylinders. The values for the tubulin oligomer coverage f, as obtained from the nonlinear fit, are indicated on the right side. The schematic represents a perpendicular cut through the MT–membrane–tubulin complex wall, corresponding to Δρ(r). (d) State diagram: f as a function of xCL or the membrane charge density, σ, when lipids can fully cover the MTs. Each data point is based on scattering data and models as in (a)–(c). Solid squares correspond to RCL/T = 160xCL. Open symbols represent different RCL/T values, as indicated in the figure. For 0 < xCL ≤ 0.1 we initially get f = 0 (corresponding to the BOR structure). Over time (Δt ~ 60 h), we obtain LPNs with higher f values as indicated by the arrows.

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