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Originally published as Biophys J. BioFAST on December 8, 2006.
doi:10.1529/biophysj.106.098459
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Biophysical Journal 92:1512-1521 (2007)
© 2007 The Biophysical Society

Actin Polymerization upon Processive Capping by Formin: A Model for Slowing and Acceleration

Tom Shemesh and Michael M. Kozlov

Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel

Correspondence: Address reprint requests to Michael M. Kozlov, Tel.: 972-3-640-7863; E-mail: michk{at}post.tau.ac.il.

Formin family proteins act as processive cappers of actin filaments, and determine the dynamics of a number of intracellular processes that are based on actin polymerization. The rate of filament growth upon processive capping varies within a broad range depending on the formin type and presence of profilin. While FH2 domains of various formins slow down polymerization by different extents, the FH1-FH2 domains in conjunction with profilin accelerate the reaction. Study of the physical mechanism of processive capping is vital for understanding the intracellular actin dynamics. We propose a model predicting that variation of a single physical parameter—the effective elastic energy of the formin-capped barbed end—results in the observed diversity of the polymerization rates. The model accounts for the whole range of the experimental results including the drastic slowing down of polymerization by FH2 of Cdc12 formin and the 4.5-fold acceleration of the reaction by FH1-FH2 of mDai1 formin in the presence of profilin. Fitting the theoretical predictions to the experimental curves provides the values of the effective elastic energies of different formin-barbed end complexes.






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Copyright © 2007 by the Biophysical Society.