Originally published as Genetics Published Articles Ahead of Print on May 4, 2007.

Genetics, Vol. 176, 1527-1539, July 2007, Copyright © 2007
doi:10.1534/genetics.107.072066

Biochemical and Genetic Analyses Provide Insight Into the Structural and Mechanistic Properties of Actin Filament Disassembly by the Aip1p–Cofilin Complex in Saccharomyces cerevisiae

Michael G. Clark1 and David C. Amberg2

Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, New York 13210

2 Corresponding author: Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, 750 E. Adams St., Syracuse, NY 13210.
E-mail: ambergd{at}upstate.edu

Explication of the Aip1p/cofilin/actin filament complex may lead to a more detailed understanding of the mechanisms by which Aip1p and cofilin collaborate to rapidly disassemble filaments. We further characterized the actin–Aip1p interface through a random mutagenic screen of ACT1, identifying a novel Aip1p interaction site on actin. This finding is consistent with our current ternary complex model and offers insights into how Aip1p may disturb intersubunit contacts within an actin filament. In addition, site-directed mutagenesis aimed at interfering with salt bridge interactions at the predicted Aip1p–cofilin interface revealed hyperactive alleles of cof1 and aip1 that support the ternary complex model and suggest that conformational changes in cofilin structure may be transmitted to actin filaments, causing increased destabilization. Furthermore, these data support an active role for Aip1p in promoting actin filament turnover.