Extended Data Fig. 3: Microtubules can sustain cycles of compression without fatigue.

(a-d) The compression (blue) and relaxation (red) force-strain curves (a and c) and the strains with maximum energy absorption efficiency (b and d) of one GMPCPP-stabilized TBA-2/TBB-2 (a and b) or MEC-12/MEC-7 (c and d) microtubule after compression-relaxation cycles. Similar results were observed in at least three independent experiments. (e and f) Schematic of the line scan analysis (e) and the corresponding intensity profiles (f) of TBA-2/TBB-2 microtubule cross-sections (green lines) before compression and at the maximum strain in the optical trap experiments. (g) Intensity profiles of the cross-section line scans from another seven TBA-2/TBB-2 microtubules at the maximum strain. (h and i) Schematic of the line scan analysis (h) and the corresponding intensity profiles (i) of MEC-12/MEC-7 microtubule cross-sections (green lines) before compression and at the maximum strain in the optical trap experiments. (j) Intensity profiles of the cross-section line scans from another seven MEC-12/MEC-7 microtubules at the maximum strain. The background threshold (red dashed lines) was determined from the mean (µ, blue dashed lines) and standard deviation (σ) of the fluorescence intensity of a 40-pixel x 40-pixel area (red squares). We used the fluorescence intensity half-heights (gray dashed line) to determine the width of peaks from microtubule cross-section line scans. The peak width of microtubules before compression was indicated (blue double arrow). All eight GMPCPP-stabilized TBA-2/TBB-2 microtubules remain intact at the maximum strain as (i) the fluorescence intensities are larger than the background threshold (red dashed lines) and (ii) the peak widths of microtubules at the maximum strain are larger than 90% of the width before compression (blue double arrows). All eight GMPCPP-stabilized MEC-12/MEC-7 microtubules are splayed at the maximum strain as the fluorescence intensities are lower than the background threshold (red dashed lines). Scale bars: 3 µm. The data are from at least three independent experiments.