title: Cofilin and DNase I affect the conformation of the small domain of actin.
abstract: 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 A (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 A), 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 A) 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.
authors.affiliation: Muscle Research Unit, Institute for Biomedical Research, Department of Anatomy and Histology, University of Sydney, NSW 2006, Australia.
authors.forename: Irina V
authors.initials: IV
authors.lastname: Dedova
authors.forename: Vadim N
authors.initials: VN
authors.lastname: Dedov
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Nosworthy
authors.forename: Brett D
authors.initials: BD
authors.lastname: Hambly
authors.forename: Cris G
authors.initials: CG
authors.lastname: dos Remedios
mesh_terms: D051339:Actin Depolymerizing Factors; D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D003850:Deoxyribonuclease I / Q000378:metabolism*; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008840:Microfilament Proteins / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011817:Rabbits; D013050:Spectrometry, Fluorescence
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D005456:Fluorescent Dyes; D008840:Microfilament Proteins; D003850:Deoxyribonuclease I