Mechanism of actin filament severing and capping by gelsolin.

Gelsolin is the prototypical member of a family of Ca-activated F-actin severing and capping proteins. Here we report structures of Ca-bound human gelsolin at the barbed end of F-actin. One structure reveals gelsolin's six domains (G1G6) and interdomain linkers wrapping around F-actin, while another shows domains G1G3-a fragment observed during apoptosis-binding on both sides of F-actin.

Mechanism of Actin Filament Severing and Capping by Gelsolin.

Gelsolin is the prototypical member of a family of Ca -dependent F-actin severing and capping proteins. A structure of Ca -bound full-length gelsolin at the barbed end shows domains G1G6 and the inter-domain linkers wrapping around F-actin. Another structure shows domains G1G3, a fragment produced during apoptosis, on both sides of F-actin.

Myosin-I synergizes with Arp2/3 complex to enhance the pushing forces of branched actin networks.

Class I myosins (myosin-Is) colocalize with Arp2/3 complex-nucleated actin networks at sites of membrane protrusion and invagination, but the mechanisms by which myosin-I motor activity coordinates with branched actin assembly to generate force are unknown. We mimicked the interplay of these proteins using the "comet tail" bead motility assay, where branched actin networks are nucleated by the Arp2/3 complex on the surface of beads coated with myosin-I and nucleation-promoting factor. We observed that myosin-I increased bead movement efficiency by thinning actin networks without affecting growth rates.

Myosin-I Synergizes with Arp2/3 Complex to Enhance Pushing Forces of Branched Actin Networks.

Myosin-Is colocalize with Arp2/3 complex-nucleated actin networks at sites of membrane protrusion and invagination, but the mechanisms by which myosin-I motor activity coordinates with branched actin assembly to generate force are unknown. We mimicked the interplay of these proteins using the "comet tail" bead motility assay, where branched actin networks are nucleated by Arp2/3 complex on the surface of beads coated with myosin-I and the WCA domain of N-WASP. We observed that myosin-I increased bead movement efficiency by thinning actin networks without affecting growth rates.

Mechanism of synergistic activation of Arp2/3 complex by cortactin and WASP-family proteins.

Cortactin coactivates Arp2/3 complex synergistically with WASP-family nucleation-promoting factors (NPFs) and stabilizes branched networks by linking Arp2/3 complex to F-actin. It is poorly understood how cortactin performs these functions. We describe the 2.