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© The Rockefeller University Press,
0021-9525/2001//75 $5.00
The Journal of Cell Biology, Volume 153, Number 1,
, 2001 75-86
Original Article |
Actin Depolymerizing Factor Stabilizes an Existing State of F-Actin and Can Change the Tilt of F-Actin Subunits
egelman{at}virginia.edu
Proteins in the actin depolymerizing factor (ADF)/cofilin family are essential for rapid F-actin turnover, and most depolymerize actin in a pH-dependent manner. Complexes of human and plant ADF with F-actin at different pH were examined using electron microscopy and a novel method of image analysis for helical filaments. Although ADF changes the mean twist of actin, we show that it does this by stabilizing a preexisting F-actin angular conformation. In addition, ADF induces a large (
12°) tilt of actin subunits at high pH where filaments are readily disrupted. A second ADF molecule binds to a site on the opposite side of F-actin from that of the previously described ADF binding site, and this second site is only largely occupied at high pH. All of these states display a high degree of cooperativity that appears to be an integral part of F-actin.
Key Words: actin ADF cooperativity electron microscopy image processing
© 2001 The Rockefeller University Press
Abbreviations used in this paper: ADF, actin depolymerizing factor; h-ADF, human ADF; IHRSR, iterative helical real space reconstruction; p-ADF, plant A. thaliana ADF1.
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