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We review how motile cells regulate actin filament assembly at their leading edge. Activation of cell surface receptors generates signals (including activated Rho family GTPases) that converge on integrating proteins of the WASp family (WASp, N-WASP, and Scar/WAVE). WASP family proteins stimulate Arp2/3 complex to nucleate actin filaments, which grow at a(More)
Metazoan cells harness the power of actin dynamics to create cytoskeletal arrays that stimulate protrusions and drive intracellular organelle movements. In plant cells, the actin cytoskeleton is understood to participate in cell elongation; however, a detailed description and molecular mechanism(s) underpinning filament nucleation, growth, and turnover are(More)
The 70 C-terminal amino acids of Wiskott-Aldrich syndrome protein (WASp WA) activate the actin nucleation activity of the Arp2/3 complex. WASp WA binds both the Arp2/3 complex and actin monomers, but the mechanism by which it activates the Arp2/3 complex is not known. We characterized the effect of WASp WA on actin polymerization in the absence and presence(More)
Formins are actin-organizing proteins that are involved in cytokinesis and cell polarity. In the plant Arabidopsis thaliana, there are more than 20 formin homologues, all of which have unknown roles. In this study, we characterize specific cellular and molecular functions of the Arabidopsis formin AtFH5. Despite the low identity of AtFH5 to yeast and(More)
Most nucleated cells crawl about by extending a pseudopod that is driven by the polymerization of actin filaments in the cytoplasm behind the leading edge of the plasma membrane. These actin filaments are linked into a network by Y-branches, with the pointed end of each filament attached to the side of another filament and the rapidly growing barbed end(More)
The evolutionarily conserved Arp2/3 complex has been shown to activate actin nucleation and branching in several eukaryotes, but its biological functions are not well understood in multicellular organisms. The model plant Arabidopsis provides many advantages for genetic dissection of the function of this conserved actin-nucleating machinery, yet the(More)
A dynamic network of polymers, the actin cytoskeleton, co-ordinates numerous fundamental cellular processes. In pollen tubes, organelle movements and cytoplasmic streaming, organization of the tip zone, vesicle trafficking, and tip growth have all been linked to actin-based function. Further, during the self-incompatibility response of Papaver rhoeas,(More)
The organization of actin filaments into large ordered structures is a tightly controlled feature of many cellular processes. However, the mechanisms by which actin filament polymerization is initiated from the available pool of profilin-bound actin monomers remain unknown in plants. Because the spontaneous polymerization of actin monomers bound to profilin(More)
We characterized the interaction of Acanthamoeba actophorin, a member of ADF/cofilin family, with filaments of amoeba and rabbit skeletal muscle actin. The affinity is about 10 times higher for muscle actin filaments (Kd = 0.5 microM) than amoeba actin filaments (Kd = 5 microM) even though the affinity for muscle and amoeba Mg-ADP-actin monomers (Kd = 0.1(More)
Actin filament bundles are higher-order cytoskeletal structures that are crucial for the maintenance of cellular architecture and cell expansion. They are generated from individual actin filaments by the actions of bundling proteins like fimbrins, LIMs, and villins. However, the molecular mechanisms of dynamic bundle formation and turnover are largely(More)