Antagonistic effects of cofilin, beryllium fluoride complex, and phalloidin on subdomain 2 and nucleotide-binding cleft in F-actin.
Cofilin/ADF, beryllium fluoride complex (BeFx), and phalloidin have opposing effects on actin filament structure and dynamics. Cofilin/ADF decreases the stability of F-actin by enhancing disorder in subdomain 2, and by severing and accelerating the depolymerization of the filament. BeFx and phalloidin stabilize the subdomain 2 structure and decrease the critical concentration of actin, slowing the dissociation of monomers. Yeast cofilin, unlike some other members of the cofilin/ADF family, binds to F-actin in the presence of BeFx; however, the rate of its binding is strongly inhibited by BeFx and decreases with increasing pH. The inhibition of the cofilin binding rate increases with the time of BeFx incubation with F-actin, indicating the existence of two BeFx-F-actin complexes. Cofilin dissociates BeFx from the filament, while BeFx does not bind to F-actin saturated with cofilin, presumably because of the cofilin-induced changes in the nucleotide-binding cleft of F-actin. These changes are apparent from the increase in the fluorescence intensity of F-actin bound epsilon-ADP upon cofilin binding and a decrease in its accessibility to collisional quenchers. BeFx also affects the nucleotide-binding cleft of F-actin, as indicated by an increase in the fluorescence intensity of epsilon-ADP-F-actin. Phalloidin and cofilin inhibit, but do not exclude each other binding to their complexes with F-actin. Phalloidin promotes the dissociation of cofilin from F-actin and slowly reverses the cofilin-induced disorder in the DNase I binding loop of subdomain 2.
Muhlrad
Andras
A
Institute of Dental Sciences, School of Dental Medicine, Department of Pharmacology, School of Pharmacy, Hebrew University of Jerusalem, Jerusalem, Israel. muhlrad@cc.huji.ac.il
Ringel
Israel
I
Pavlov
Dmitry
D
Peyser
Y Michael
YM
Reisler
Emil
E
D008841:Actin Cytoskeleton / Q000737:chemistry; D051339:Actin Depolymerizing Factors / Q000737:chemistry*; D000199:Actins / Q000037:antagonists & inhibitors / Q000737:chemistry*; D000244:Adenosine Diphosphate / Q000737:chemistry*; D000818:Animals; D001608:Beryllium / Q000737:chemistry*; D001665:Binding Sites; D005459:Fluorides / Q000737:chemistry*; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry; D010590:Phalloidine / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D011817:Rabbits
D051339:Actin Depolymerizing Factors; D000199:Actins; D005656:Fungal Proteins; D010590:Phalloidine; C056920:beryllium trifluoride; D000244:Adenosine Diphosphate; D001608:Beryllium; D005459:Fluorides