A new hat for Aip1: Uncovering new roles for Aip1 in the disassembly of filamentous actin

Left Image: Model Representing Mode of Aip1 Action on Cofilin-Actin Filaments (A) Cofilin alone binds to the filament and alters the angular configuration of actin protomers within the polymer lattice. Severing is caused due to unstable heterotypic junctions between cofilin-bound and unbound regions on the actin filament. (B) Aip1 preferentially binds stretches of actin polymer occupied with cofilin leading to enhanced severing and faster disassembly from both barbed and pointed ends. (C) In the presence of Aip1, cofilin-saturated filaments are no longer stable and can be destabilized. Right Image: Summary of Stable to Unstable cofilin-actin polymer with Aip1

Disassembly of actin filaments is important for many processes that involve rapid reorganization of cell shape such as cell movement and division. Cofilin is a vital disassembly protein however one limitation of cofilin is that it can stabilize filaments at saturating concentrations. Nadkarni and Brieher showed that the amount of cofilin in thymus extract is too high to allow disassembly of single actin filaments in solution. They discovered that Aip1 is able to disassemble filaments even in the presence of stabilizing concentrations of cofilin.

In the presence of Aip1, stable filaments underwent increased severing and disassembly at filament ends. This indicated that Aip1 could act all along the sides of cofilin-decorated actin filaments. However, previous work had shown that Aip1 was a capping factor that acted at filament ends. Nadkarni and Brieher went on to show that Aip1 acts differently than a well-characterized capping factor CapZ, and does not behave like a capping factor. This led to a revision of the view of Aip1's mode of action on actin filaments.

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February 25, 2015 All News