Fig. 2: Light-induced actin polymerization on a supported lipid bilayer (SLB).

a Schematic illustration of the OptoVCA system for in vitro experiments. Upon blue light illumination, actin polymerization is triggered by the recruitment of SspB-mScarlet-I-VCA to the SLB. Condition: 5 μM Actin, 15 μM Profilin, 100 nM Arp2/3 complex, 25 nM CP, and 150 nM SspB-mScarlet-I-VCA. Representative images of the recruitment of SspB-mScarlet-I-VCA (upper panels) and subsequent actin polymerization (lower panels) on 6% DGS-NTA(Ni) lipid (b) and 2% DGS-NTA(Ni) lipid (c) at each indicated time point. Blue squares indicate the light-illuminated regions with 1 nW/μm². All scale bars, 20 μm. Fluorescence intensities of SspB-mScarlet-I-VCA (d) and Alexa647-actin (e) on 2% or 6% DGS-NTA(Ni) lipid. The mean values (bold lines) are plotted as a function of time with the SD. n = 12 for each condition. f Three-dimensional reconstructed image of polymerized actin on 6% DGS-NTA(Ni) lipid (left) and 2% DGS-NTA(Ni) lipid (right) after 20 min light illumination. g High-speed imaging of the recruitment of SspB-mScarlet-I-VCA (upper panels) and subsequent actin polymerization (lower panels) on 6% DGS-NTA(Ni) lipid. Blue-squared regions were illuminated with 1 nW/μm². Orange-squared regions in the lower panels are magnified and shown as the inset images. Scale bars, 20 μm and 5 μm for the wide-view images and the inset images, respectively. h Growth dynamics of a single actin network seed quantified by the line scan along red dashed lines in the inset images of (g). Source data are provided as a Source Data file.