Multimodal and Polymorphic Interactions between Anillin and Actin: Their Implications for Cytokinesis

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• Cytokinesis, the process of cell division, relies on the contractile ring.
• Anillin is a crucial scaffold protein for contractile ring assembly and function.
• The precise role of anillin's actin-binding domain (ActBD) in cytokinesis is not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanisms by which anillin interacts with filamentous actin (F-actin).
• To determine the contribution of anillin's actin-binding sites to its function in cytokinesis.

Main Methods:

• Depletion-and-rescue assays in Drosophila S2 cells.
• In vitro binding assays and electron microscopy on recombinant anillin fragments.
• Live-cell imaging to assess protein localization and function.

Main Results:

• Anillin lacking the actin-binding domain (ActBD) shows impaired cortical localization and cytokinesis.
• The anillin ActBD contains three distinct actin-binding sites (ABS1-3), each interacting with F-actin differently.
• ABS1 and ABS3 bind mutually exclusively to F-actin.
• ABS2 and ABS3 are sufficient for F-actin bundling, while ABS1 modulates bundling and promotes 3D F-actin structures.
• ABS2 and ABS3 are essential for anillin's cortical localization during cytokinesis.

Conclusions:

• Multiple modes of anillin-actin interaction are critical for proper cytokinesis.
• The specific actin-binding sites on anillin play distinct roles in F-actin organization and cell division.