Figure 1.

Reversible in situ formation of PLys/ATP coacervates in lipid vesicles by a reduction in pH. A) Polylysine (PLys) switches between a cationic polymer to an uncharged polymer at its pK _a of pH 10.5. B) Cartoon depicting the pH‐controlled formation of coacervate microdroplets within giant vesicles. C i–E i) Fluorescent confocal images of GUVs made from POPC/Cholesterol containing PLys and ATP at a 4:1 molar ratio. Scale bar=5 μm. C) At pH 11, after washing the outer solution with iso‐osmolar pH 11 buffer solution, D) at pH 9, after the addition of iso‐osmolar pH 7.3 buffer, and E) after returning the pH to pH 11. C ii–E ii) Corresponding intensity profiles (along the white dashed line) of confocal images of DiD fluorescence (magenta) and FITC‐PLys fluorescence (cyan). Fluorescence intensities were normalized by the maximum intensity. F) FRAP of coacervate microdroplets in lipid vesicles. Confocal fluorescence microscopy images of a PLys/ATP coacervate in a GUV before bleaching (i); at bleaching (t=0; ii); and after recovery (3 s; iii). Scale bar=5 μm. G) Corresponding FRAP recovery curves for FITC‐PLys. The raw data (shaded gray), mean (dark blue), and 95 % confidence limit (light blue) from 16 experiments are shown. The recovery profile was fit to a double exponential curve to obtain the fast and slow diffusion coefficients: 2.4±1.4 μm² s⁻¹ and 0.4±0.17 μm² s⁻¹.