Individual actin has several structures.

<p>(A) G-actin has 4 subdomains. Residues 41 (D-loop region in subdomain 2) and 374 (C-terminal region in subdomain 1) were labeled with Alexa dyes of different wavelengths. (B) Fluorescent images of the acceptor (left images) and donor (right images) captured simultaneously by an electron multiplying charged coupled device camera. (i) and (ii) indicate the donors and acceptors for different individual actin molecules, respectively. The corresponding Förster resonance energy transfer (FRET) efficiencies of (i) and (ii) are shown in (C) and (D), respectively. The scale bar is 5 µm. (C–E) Time series of the acceptor and donor intensities from different single G-actin molecules and the corresponding FRET efficiency histograms. Two states can be seen. (F) Time series of the acceptor and donor intensities from a single F-actin molecule and the corresponding FRET efficiency histogram. A state distinct from that observed in G-actin can be seen.