Comparison between experimental results and Virtual Cell biochemical model predictions from simulations using different mechanisms of Arp2/3 activation. (A–D) Quantitative Virtual Cell biochemical simulations were performed using three different mechanisms of N-WASp (NW) and Arp2/3 complex activation, five different aggregate sizes, six different aggregate velocities, and seven different Nck SH3 densities. Models were simulated using experimentally measured aggregate sizes, velocities, and densities. Simulation results were weighted based on experimentally measured aggregate size and velocity distributions to allow for an accurate comparison of predicted and experimental results. The plots show comparisons of simulation results from models using one Nck/one N-WASp/one Arp2/3, two Nck/two N-WASp/one Arp2/3, or four Nck/two N-WASp/one Arp2/3 with experimentally measured actin comet tail length (A), number of actin molecules in the comet tail core (B), peak actin concentration (C), and distance between aggregate centroid and peak actin concentration (D). For each measured actin comet tail characteristic, the 4:2:1 Nck/N-WASp/Arp2/3 activation scheme best predicted experimental results, suggesting that this mechanism, and not the 1:1:1 or 2:2:1 mechanism, was responsible for the activation of Arp2/3 downstream of Nck SH3 domains. For graphs on right, data have been normalized to the maximum values within each group to allow for another comparison of predicted and experimental results. The data for the experimental datasets are duplicated from Fig. 4 for comparison with model predictions.