Single-Turnover Activation of Arp2/3 Complex by Dip1 May Balance Nucleation of Linear versus Branched Actin Filaments

Abstract

Dip1 May Balance Nucleation of Linear versus Branched Actin Filaments Highlights d Dip1 stimulates assembly of disconnected linear actin filament networks d Dip1 is a single-turnover activator of Arp2/3 complex d Dip1 incorporates into actin filament networks at endocytic sites d Single-turnover activation of nucleation by Dip1 may limit linear filament creation

Synergy between Wsp1 and Dip1 may initiate assembly of endocytic actin networks

“…We anticipate that synergistic activation by Wsp1 and Dip1 is limited by the same mechanisms that prevent Dip1 alone from activating too many Arp2/3 complexes at endocytic sites. For instance, we showed previously that when Dip1 activates on its own, it remains bound to Arp2/3 complex long after nucleation, unlike Wsp1, so each Dip1 molecule likely only activates one Arp2/3 complex (Balzer et al, 2019). We found here that even when it activates with Wsp1, Dip1 stays bound to Arp2/3 complex on the ends of filaments long after nucleation, so Dip1 likely functions as a single turnover NPF in the context of synergistic activation (Fig.…”

“…2). Combined with the low concentration of Dip1 at endocytic actin patches, this single turnover mechanism may help limit the number of linear filaments created at endocytic sites (Balzer et al, 2019; Basu and Chang, 2011). Competition with actin filaments may provide a second mechanism for limiting linear filaments generated through synergy between Wsp1 and Dip1.…”

Synergy between Wsp1 and Dip1 may initiate assembly of endocytic actin networks

“…We asked if this simplified model could fit time courses of actin polymerization for reactions containing both Dip1 and Wsp1 if the rate constants of key steps were increased. We limited the fitting to reactions with Dip1 concentrations greater than 0.5 µM, as higher concentrations of Dip1 limit the contribution of branching nucleation to actin assembly ( Balzer et al, 2019 ). This allowed us to ignore the action of Wsp1 alone on Arp2/3 complex in the simulated reactions.…”

“…We anticipate that synergistic activation by Wsp1 and Dip1 is limited by the same mechanisms that prevent Dip1 alone from activating too many Arp2/3 complexes at endocytic sites. For instance, we showed previously that when Dip1 activates on its own, it remains bound to Arp2/3 complex long after nucleation, unlike Wsp1, so each Dip1 molecule likely only activates one Arp2/3 complex ( Balzer et al, 2019 ). We found here that even when it activates with Wsp1, Dip1 stays bound to Arp2/3 complex on the ends of filaments long after nucleation, so Dip1 likely functions as a single turnover NPF in the context of synergistic activation ( Figure 2 ).…”

“…We found here that even when it activates with Wsp1, Dip1 stays bound to Arp2/3 complex on the ends of filaments long after nucleation, so Dip1 likely functions as a single turnover NPF in the context of synergistic activation ( Figure 2 ). Combined with the low concentration of Dip1 at endocytic actin patches, this single turnover mechanism may help limit the number of linear filaments created at endocytic sites ( Balzer et al, 2019 ; Basu and Chang, 2011 ). Competition with actin filaments may provide a second mechanism for limiting linear filaments generated through synergy between Wsp1 and Dip1.…”