The second ADF/cofilin actin-binding site exists in F-actin, the cofilin-G-actin complex, but not in G-actin.
ADF/cofilins are actin binding proteins that bind actin close to both the N- and C-termini (site 1), and we have found a second cofilin binding site (site 2) centered around helix 112-125 [Renoult, C., Ternent, D., Maciver, S.K., Fattoum, A., Astier, C., Benyamin, Y. & Roustan, C. (1999) J. Biol. Chem. 274, 28893-28899]. We proposed a model in which ADF/cofilin intercalated between subdomains 1 and 2 of two longitudinally associated actin monomers within the actin:cofilin cofilament, explaining the change in twist that ADF/cofilins induce in the filament [McGough, A. Pope, B., Chiu, W. & Weeds, A. (1998) J. Cell Biol. 138, 771-781]. Here, we have determined the fuller extent of the cofilin footprint on site 1 of actin. Site 1 is primarily the G-actin binding site. Experiments with both peptide mimetics and fluorescently labeled cofilin suggest that site 2 only becomes available for cofilin binding within the filament, possibly due to motion between subdomains 1 and 2 within an actin monomer. We have detected motion between subdomains 1 and 2 of G-actin by FRET induced by cofilin, to reveal the second cofilin-binding site. This motion may also explain how cofilins inhibit the nucleotide exchange of actin, and why the actin:cofilin complex is polymerizable without dissociation.
Blondin
L
L
UMR 5539 (CNRS) Laboratoire de motilité cellulaire (Ecole Pratiques des Hautes Etudes), Université de Montpellier 2, France.
Sapountzi
V
V
Maciver
S K
SK
Renoult
C
C
Benyamin
Y
Y
Roustan
C
C
D051339:Actin Depolymerizing Factors; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001704:Biopolymers; D051345:Destrin; D004735:Energy Transfer; D004797:Enzyme-Linked Immunosorbent Assay; D006863:Hydrogen-Ion Concentration; D008840:Microfilament Proteins / Q000378:metabolism*; D008958:Models, Molecular; D011817:Rabbits; D013050:Spectrometry, Fluorescence
D051339:Actin Depolymerizing Factors; D000199:Actins; D001704:Biopolymers; D051345:Destrin; D008840:Microfilament Proteins