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Biophys J, June 2002, p. 3134-3143, Vol. 82, No. 6

Cofilin and DNase I Affect the Conformation of the Small Domain of Actin

Irina V. Dedova,* Vadim N. Dedov,* Neil J. Nosworthy,* Brett D. Hambly,dagger and Cris G. dos Remedios*

 *Muscle Research Unit, Institute for Biomedical Research, Department of Anatomy and Histology, and  dagger Department of Pathology, The University of Sydney, NSW 2006, Australia

Cofilin binding induces an allosteric conformational change in subdomain 2 of actin, reducing the distance between probes attached to Gln-41 (subdomain 2) and Cys-374 (subdomain 1) from 34.4 to 31.4 Å (pH 6.8) as demonstrated by fluorescence energy transfer spectroscopy. This effect was slightly less pronounced at pH 8.0. In contrast, binding of DNase I increased this distance (35.5 Å), a change that was not pH-sensitive. Although DNase I-induced changes in the distance along the small domain of actin were modest, a significantly larger change (38.2 Å) was observed when the ternary complex of cofilin-actin-DNase I was formed. Saturation binding of cofilin prevents pyrene fluorescence enhancement normally associated with actin polymerization. Changes in the emission and excitation spectra of pyrene-F actin in the presence of cofilin indicate that subdomain 1 (near Cys-374) assumes a G-like conformation. Thus, the enhancement of pyrene fluorescence does not correspond to the extent of actin polymerization in the presence of cofilin. The structural changes in G and F actin induced by these actin-binding proteins may be important for understanding the mechanism regulating the G-actin pool in cells.

Biophys J, June 2002, p. 3134-3143, Vol. 82, No. 6
© 2002 by the Biophysical Society   0006-3495/02/06/3134/10  $2.00


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