Fig. 2: Heimdallarchaeota encoded actin (heimActin) and rabbit actin polymerization are modulated by heimProfilin.

Time dependent Total Internal Reflection Fluorescence (TIRF) Microscopy of (a) 1 μM of rabbit actin labeled with 0.3% Alexa Fluor 568 and 0.2% Biotin-actin supplemented with 100 μM of heimProfilin, profilin mutants or thorProfilin. b–c Electron microscopy (EM) images (at 100 nm scale) of heimActin (b) forming thin, uniform filamentous polymers and ΔC-heimActin (c) forming irregular, amorphous structures. Scale bar: 100 nm. d Pyrene-polymerization profiles of 1 μM rabbit actin (2% pyrene-labeled) alone or supplemented with 0.3 μM actin seeds with different concentrations of heimProfilin; 1 μM actin alone (light green), 1 μM actin with 0.3 μM actin seed (dark green), 50 μM (red), 100 μM (cyan), 200 μM (yellow), 280 μM (orange), 200 μM (blue) with 0.3 μM actin seed, and 250 μM (black) with 0.3 μM actin seed. e Pyrene-polymerization profiles of 1 μM of rabbit actin (2% pyrene-labeled) alone or supplemented with 0.3 μM actin seeds with different concentrations of ΔN-heimProfilin; 1 μM actin alone (red), 1 μM actin with 0.3 μM actin seed (dark green), 50 μM (cyan), 200 μM (yellow), 280 μM (orange), 100 μM (blue) with 0.3 μM actin seed, 200 μM (black) with 0.3 μM actin seed and 250 μM (light green) with 0.3 μM actin seed. f initial slopes of the pyrene polymerization assays in (d) and (e) plotted as a function of heimProfilin and ΔN-heimProfilin concentrations. The slopes were obtained from the linear phase of the reaction after removing the lag phase. g ATP hydrolysis during polymerization of heimActin (cyan, green, purple and blue) or ΔC-heimActin (brown, red, orange, and dark-red) as a function of temperature. Four replicates from each experiment is plotted as function of temperature.