Figure 4.

Dependence of on-rate constants on local tip structure. (A) Estimated on-rate constants of freely diffusing subunits for all possible local configurations are shown. Rates for simulations with (lighter) and without (darker) the lateral bond result in equivalent estimates of the on-rate constant. (B) Efficiency of diffusive arrivals to 10-nm center-to-center distance and subsequent binding are shown. Each is normalized to the respective zero neighbor case. (C and D) On-rate penalties (fold decrease from the zero neighbor case) for the single- (C) and two- (D) neighbor cases with (lighter) and without (darker) lateral bonds. Penalties were estimated across a range of tolerances, where tolerance is defined as the minimum distance between adjacent protofilaments within the microtubule lattice. (E) Estimated on-rate constants of G-actin binding to the leading and lagging protofilament are shown (lateral neighbor numbers are illustrated in Fig. 1A) for simulations with (lighter) and without (darker) the diagonal bonds. All error bars are mean ± SE.