FIGURE 3.

Simulated growing microtubule tips have either blunt ends or short sheetlike extensions. Microtubules started in a blunt, GTP-capped configuration in the presence of 10 μM tubulin-GTP (k₍₊₎ = 2 × 10⁶ M⁻¹ s⁻¹). GTP-caps were initialized to four layers of dimers (52 dimers total) and simulations were allowed to run for 1000 events, including association, dissociation, and hydrolysis, to produce the final configurations shown. (A, C, and E) Structure and GTP state of growing microtubule tips, three typical examples of assembly. Green monomers are α-tubulin. White monomers are β-tubulin with GDP content. Red monomers are β-tubulin with GTP content. (B, D, and F) Mechanochemical energy state of microtubule tips. The same microtubules represented in A, C, and E, respectively, are used to show mechanochemical energy state. Spectral color-coding indicates total chemical and mechanical energy for each dimer as given in the color scale to the right, with red being most stable and white the least.