Fig. 2: Role of lateral tubulin activation energy for MT dynamics and force generation.
a Visualization of an MT, β- and α-tubulins depicted as in Fig. 1. Each tubulin monomer has two lateral and two longitudinal interaction sites (black dots). b Energy of longitudinal interaction between tubulin monomers as a function of distance between the interaction sites. Formula below describes the shape of longitudinal tubulin energy potentials. c A set of energy curves, describing lateral tubulin−tubulin interactions as a function of distance with different lateral activation energies (alat). Strength of the lateral bond, blat, equals 6 kcal mol−1 in this example. d Dependence of MT growth or shortening rate on the lateral bond strength, blat, for different lateral barrier parameters, alat. Numbers less than zero imply shortening. e Dependence of PF curl length on the strength of the lateral bond, blat, graphed for several lateral activation energies, alat. f Dependence of MT shortening rate on opposing force in simulations. The strength of the lateral bonds between the tubulins (blat) was set to be weak, representing tubulins in the GDP state. Specifically, with each activation barrier height (alat), blat was selected to enable shortening at ~400 nm s−1. See Source Data file for a full list of parameter values in all simulations. g Dependence of MT growth rate on opposing force in simulation and experiment. Tubulins were configured to have strong lateral bonds, blat = 8 kcal mol−1, to represent the GTP-state of tubulins. No GTP hydrolysis was allowed. Data points, describing simulation results in all graphs in this figure, represent mean ± s.d. based on 3–6 repeats of each simulation. Source data are provided as a Source Data file.
