Visualizing dynamic actin cross-linking processes driven by the actin-binding protein anillin.

Anillin is a type of actin filament cross-linking protein that stabilizes the actin-based contractile ring during cytokinesis. To elucidate the underlying intermolecular interactions between actin filaments and anillin, we utilized total internal reflection fluorescence microscopy (TIRFM) and high-speed atomic force microscopy (Hs-AFM). Single-molecule imaging of anillin using TIRFM showed that anillin exists as monomers with relatively low binding affinity for actin filaments. Real-time imaging of actin filament cross-linking dynamics induced by anillin using Hs-AFM revealed that anillin monomers cross-link with actin filaments at a distance of 8 nm and that the polarity of those filaments is both parallel and antiparallel. These results are consistent with anillin playing a role in actin ring transition in vivo, where it might be responsible for thinning the ring-shaped apolar actin bundles.