Fig. 8: Change in the microtubule (MT) wall-to-wall spacing, upon transitioning from the wide-spacing (Bws) to the intermediate (Bint) MT bundle state, correlates with tubulin ring proliferation.
Wall-to-wall spacings (dw-w = ah – 2[rin + w]) plotted as a function of time for the series of Ca2+ (A) and Mg2+ (C) samples (SAXS data shown in Figs. 2 and 7, respectively). Some data points omitted for clarity. Arrows indicate the latest time point at which the Bws state is observed before the sample transitions to the Bint state. Fitted tubulin ring scattering amplitude plotted as a function of time for the same series of Ca2+ (B) and Mg2+ (D) samples. Amplitudes are normalized by the maximum ring scattering measured. Arrows indicate the latest time point at which the bundled wide-spacing (Bws) state is observed before the sample transitions to the bundled intermediate (Bint) state, with increases in the tubulin ring scattering amplitude observed after. Comparisons between A and B for the Ca2+ series and between C and D for the Mg2+ series show that the onset of tubulin ring proliferation occurs concurrently with the transition from the Bws to the Bint state. Time “0” on the x-axis corresponds to t0, as defined in Fig. 2. All samples contained the stated Mg2+ or Ca2+ concentrations added to standard PIPES buffer at pH 6.8, which includes 1 mM of Mg2+ (see Methods). Data is provided in the Source Data file.
