WASP family proteins, more than Arp2/3 activators (original) (raw)
Related papers
Arp2/3 complex is bound and activated by two WASP proteins
Proceedings of the National Academy of Sciences, 2011
Actin related protein 2/actin related protein 3 (Arp2/3) complex nucleates new actin filaments in eukaryotic cells in response to signals from proteins in the Wiskott–Aldrich syndrome protein (WASP) family. The conserved VCA domain of WASP proteins activates Arp2/3 complex by inducing conformational changes and delivering the first actin monomer of the daughter filament. Previous models of activation have invoked a single VCA acting at a single site on Arp2/3 complex. Here we show that activation most likely involves engagement of two distinct sites on Arp2/3 complex by two VCA molecules, each delivering an actin monomer. One site is on Arp3 and the second is on ARPC1 and Arp2. The VCAs at these sites have distinct roles in activation. Our findings reconcile apparently conflicting literature on VCA activation of Arp2/3 complex and lead to a new model for this process.
Elucidating Key Motifs Required for Arp2/3-Dependent and Independent Actin Nucleation by Las17/WASP
PLOS ONE, 2016
Actin nucleation is the key rate limiting step in the process of actin polymerization, and tight regulation of this process is critical to ensure actin filaments form only at specific times and at defined regions of the cell. Arp2/3 is a well-characterised protein complex that can promote nucleation of new filaments, though its activity requires additional nucleation promotion factors (NPFs). The best recognized of these factors are the WASP family of proteins that contain binding motifs for both monomeric actin and for Arp2/3. Previously we demonstrated that the yeast WASP homologue, Las17, in addition to activating Arp2/3 can also nucleate actin filaments de novo, independently of Arp2/3. This activity is dependent on its polyproline rich region. Through biochemical and in vivo analysis we have now identified key motifs within the polyproline region that are required for nucleation and elongation of actin filaments, and have addressed the role of the WH2 domain in the context of actin nucleation without Arp2/3. We have also demonstrated that full length Las17 is able to bind liposomes giving rise to the possibility of direct linkage of nascent actin filaments to specific membrane sites to which Las17 has been recruited. Overall, we propose that Las17 functions as the key initiator of de novo actin filament formation at endocytic sites by nucleating, elongating and tethering nascent filaments which then serve as a platform for Arp2/3 recruitment and function.
Signalling to actin: the Cdc42-N-WASP-Arp2/3 connection
Chemistry & Biology, 1999
The molecular link between the signalling pathway regulating the formation of filopodia and the initiation of local actin polymerization has been elucidated: N-WASP, a close homologue of WASP, which is the prolduct of the gene responsible for the Wiskott-Aldrich syndrome, mediates a direct connection between the small G-protein Cdc42 and the Arp2/3 complex.
Scar, a WASp-related protein, activates nucleation of actin filaments by the Arp2/3 complex
Proceedings of the National Academy of Sciences, 1999
The Arp2͞3 complex, a stable assembly of two actin-related proteins (Arp2 and Arp3) with five other subunits, caps the pointed end of actin filaments and nucleates actin polymerization with low efficiency. WASp and Scar are two similar proteins that bind the p21 subunit of the Arp2͞3 complex, but their effect on the nucleation activity of the complex was not known. We report that full-length, recombinant human Scar protein, as well as N-terminally truncated Scar proteins, enhance nucleation by the Arp2͞3 complex. By themselves, these proteins either have no effect or inhibit actin polymerization. The actin monomer-binding W domain and the p21-binding A domain from the C terminus of Scar are both required to activate Arp2͞3 complex. A proline-rich domain in the middle of Scar enhances the activity of the W and A domains. Preincubating Scar and Arp2͞3 complex with actin filaments overcomes the initial lag in polymerization, suggesting that efficient nucleation by the Arp2͞3 complex requires assembly on the side of a preexisting filament-a dendritic nucleation mechanism. The Arp2͞3 complex with full-length Scar, Scar containing P, W, and A domains, or Scar containing W and A domains overcomes inhibition of nucleation by the actin monomer-binding protein profilin, giving active nucleation over a low background of spontaneous nucleation. These results show that Scar and, likely, related proteins, such as the Cdc42 targets WASp and N-WASp, are endogenous activators of actin polymerization by the Arp2͞3 complex.
Current Biology, 1998
Background: The actin-related proteins Arp2 and Arp3 are part of a sevenprotein complex which is localized in the lamellipodia of a variety of cell types, and in actin-rich spots of unknown function. The Arp2/3 complex enhances actin nucleation and causes branching and crosslinking of actin filaments in vitro; in vivo it is thought to drive the formation of lamellipodia and to be a control center for actin-based motility. The Wiskott-Aldrich syndrome protein, WASP, is an adaptor protein implicated in the transmission of signals from tyrosine kinase receptors and small GTPases to the actin cytoskeleton. Scar1 is a member of a new family of proteins related to WASP, and it may also have a role in regulating the actin cytoskeleton. Scar1 is the human homologue of Dictyostelium Scar1, which is thought to connect G-protein-coupled receptors to the actin cytoskeleton. The mammalian Scar family contains at least four members. We have examined the relationships between WASP, Scar1, and the Arp2/3 complex. Results: We have identified WASP and its relative Scar1 as proteins that interact with the Arp2/3 complex. We have used deletion analysis to show that both WASP and Scar1 interact with the p21 subunit of the Arp2/3 complex through their carboxyl termini. Overexpression of carboxy-terminal fragments of Scar1 or WASP in cells caused a disruption in the localization of the Arp2/3 complex and, concomitantly, induced a complete loss of lamellipodia and actin spots. The induction of lamellipodia by platelet-derived growth factor was also suppressed by overexpression of the fragment of Scar1 that binds to the Arp2/3 complex. Conclusions: We have identified a conserved sequence domain in proteins of the WASP family that binds to the Arp2/3 complex. Overexpression of this domain in cells disrupts the localization of the Arp2/3 complex and inhibits lamellipodia formation. Our data suggest that WASP-related proteins may regulate the actin cytoskeleton through the Arp2/3 complex.