Structural comparisons between Tuba1a, Tuba1a S140G, and Tuba8. (A) Structural superposition of time-averaged tubulin structures from WT (light green) and S140G-mutant (red) simulations. The S140G mutation is shown as well as the GTP binding sites. (B) Time evolution of intradimer angle between α-core helix H7 and β-core helix H7 in WT (green) and S140G mutant (red). The inset shows a lower angle distribution in the mutant than in WT, indicating straighter dimers for the mutant tubulin dimer. ***, P < 0.001. Data are represented as mean ± SEM. A total of 6,250 points was used. (C) The S140G mutant forms an additional salt-bridge triad (SBT) buried at the intradimer interface (highlighted in box). The α-tubulin is colored in blue, and β-tubulin is in green. (D and E) Higher magnification of intradimer interface for WT and S140G-mutant tubulin. The salt-bridge triad in the S140G mutant (highlighted in box) involves α:Asp98 with β:Arg162 and β:Arg251. The α:Asp98–β:Arg251 interaction is absent in WT. (F) Structural model superposition of Tuba1a (brown) and Tuba8 (light blue) revealed slight differences. (G) Electrostatic analysis of Tuba1a and Tuba8. The H1-S2 loop cooperates with the M loop from adjacent protofilaments. Whereas Tuba1a presents cooperative positive charges in the H1-S2 loop, Tuba8 presents a more negative charge distribution.