Abstract
Cofilin, along with other proteins that belong to the actin-depolymerization factor (ADF)/cofilin family enhance actin turnover by severing filamentous actin (F-actin). using total internal reflective fluorescence (TIRF) microscopy, we show that yeast cofilin (YCof) severs yeast F-actin effectively at low concentrations whereas high concentrations of human cofilin 1 (hCof1) are required for such severing and filament shortening. It has been suggested that the severing of actin filaments is caused by changes in their twist upon binding of cofilin. Electron microscopy (EM) 3-D reconstruction shows both YCof and hCof1 cause similar changes in the twist of yeast F-actin (5o). Cofilin/ADF affects strongly the structure of actin filaments and especially in the vicinity of intermolecular contacts of the DNase I binding loop (D-loop) in subdomain 2. This is manifested in strong cofilin-induced acceleration of D-loop cleavage in F-actin by subtilisin. Similar acceleration of D-loop cleavage by subtilisin is observed with yeast and human cofilin in yeast F-actin. These results indicate that the twist change and/or D-loop exposure to proteolytic attack are not coupled tightly to filaments severing by cofilin.
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