Cortactin binding to F-actin revealed by electron microscopy and 3D reconstruction.
Cortactin and WASP activate Arp2/3-mediated actin filament nucleation and branching. However, different mechanisms underlie activation by the two proteins, which rely on distinct actin-binding modules and modes of binding to actin filaments. It is generally thought that cortactin binds to "mother" actin filaments, while WASP donates actin monomers to Arp2/3-generated "daughter" filament branches. Interestingly, cortactin also binds WASP in addition to F-actin and the Arp2/3 complex. However, the structural basis for the role of cortactin in filament branching remains unknown, making interpretation difficult. Here, electron microscopy and 3D reconstruction were carried out on F-actin decorated with the actin-binding repeating domain of cortactin, revealing conspicuous density on F-actin attributable to cortactin that is located on a consensus-binding site on subdomain-1 of actin subunits. Strikingly, the binding of cortactin widens the gap between the two long-pitch filament strands. Although other proteins have been found to alter the structure of the filament, the cortactin-induced conformational change appears unique. The results are consistent with a mechanism whereby alterations of the F-actin structure may facilitate recruitment of the Arp2/3 complex to the "mother" filament in the cortex of cells. In addition, cortactin may act as a structural adapter protein, stabilizing nascent filament branches while mediating the simultaneous recruitment of Arp2/3 and WASP.
Pant
Kiran
K
Department of Physiology & Biophysics, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118, USA.
Chereau
David
D
Hatch
Victoria
V
Dominguez
Roberto
R
Lehman
William
W
D051377:Actin-Related Protein 2 / Q000737:chemistry / Q000378:metabolism; D051378:Actin-Related Protein 3 / Q000737:chemistry / Q000378:metabolism; D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D051356:Cortactin / Q000737:chemistry* / Q000378:metabolism*; D021621:Imaging, Three-Dimensional; D051379:Mice; D008854:Microscopy, Electron; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid
D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; D051356:Cortactin; D046912:Multiprotein Complexes