TABLE 2.
Model parameters and standard values
| Symbol | Value | Description | References |
|---|---|---|---|
| δ | 2.7 nm | Extension length of polymerizing actin monomer. | — |
| D | 6.0 μm2/s | Cytoplasmic actin monomer diffusion coefficient. | (28) |
| [A]TE | 12 μM | Fixed, trailing-edge actin monomer concentration. | (29) |
| γse | 50 pN/nm | Plasma membrane surface energy coefficient (= 50 pJ/nm2). | (8,30) |
| FL | 100 pN/μm | Total load force (linear density) against LE protrusion (= 2 γse for internal membrane forces alone, because lamellipodia contain two membrane surfaces). Higher values represent additional external loads. | — |
| fL | 15 pN | Total membrane (nontethering) load force against protrusion = FLΔx. | — |
| Δx | 150 nm | Standard width of lamellipodial LE modeled (governs nfb and fL). | — |
| κb | 80 pN nm | Bending energy coefficient, ∼20 kT. | (30) |
| Lp | 10 μm | Persistence length of actin filaments. | (31) |
| tlam | 200 nm | Lamellipodial thickness. | (29) |
| kon,brb | 12/μM/s | On-rate of actin to barbed end ≡ Rpol,b/[A]. | (32) |
| koff,brb | 1.4/s | Off-rate of actin from barbed end ≡ Rdpol,b. | (32) |
| kon,ptd | 0/μM/s | On-rate of actin to pointed end, profilin-adjusted ≡ Rpol,p/[A]. | (33) |
| koff,ptd | 8.0/s | Off-rate of actin from pointed end, cofilin-adjusted ≡ Rdpol,p. | (34) |
| ɛ | 1.5 δ | LE cap-protection/branch zone (Y) length. | (3,24) |
| Rbr | 0.43/s | (Total) rate of barbed end branching ≡ kbr [arp2/3]. | (8,24,29) |
| Rdbr | 0.05/s | Rate of debranching for any branch point. | (35) |
| koff,T | 0.5/s | Unloaded (natural) off-rate of arp2/3 activator to arp2/3. | (8) |
| Fchar,T | 2 pN | Characteristic force describing force-dependence of branch tether. | See text |
| Rcp | 6.0/s | Rate of barbed end capping ≡ kon,cp [cp]. | (36) |
| Runcp | 0/s | Uncapping rate for any capped barbed end ≡ koff,cp. | (36,37) |
| Nfb | 200 fil/μm | Forward-facing free barbed ends per LE width (indirectly specified). | (29) |
| nfb | 30 fil | Number of filaments in a 150-nm-wide LE, corresponding to Nfb. | — |
| θbr | 70° | Average branch angle. | (38) |
| σbr | 7° | Branch angle standard deviation. | (38) |
See model description and mathematical relationships in Schaus et al. (24).