Fig. 5.

Longitudinal tubulin lattice length and curvature are regulated by the MIPs. (A) Plot of tubulin dimer distances from doublet and the sarkosyl A-tubule. Mean values with SD for each PF are shown. The average value of each PF from the sarkosyl A-tubule shows a lateral compression of ∼2 Å. Statistical analysis was performed by 2-way ANOVA, Bonferroni post hoc test (see also SI Appendix, Table S2). (B) Comparison of tubulin models refined in PF-A12 from doublet (blue) and sarkosyl A-tubule (green) showing a longitudinal compaction after missing some MIPs. Models were aligned by β2-tubulin. (C) Tubulin models of PF-A12 from the doublet are colored according to the degree of displacement. Vectors of the Cα displacement toward the sarkosyl A-tubule model are shown in red. (D and E) Close-up views of the tubulins from the periphery with vectors. (F) Plot of inter-PF angles in the doublet and sarkosyl A-tubule. Inter-PF angles were measured as shown in the schematic diagram on Top and mean values were plotted (see also SI Appendix, Fig. S5C and Table S3). Error bars represent SD. Two-way ANOVA, Bonferroni post hoc test was performed to compare the mean values. PF pairs with P values smaller than 0.01 are highlighted by asterisks (see also SI Appendix, Table S4). The gray area in the plot represents the PF pair angles commonly seen for in vitro reconstituted singlets (29). (G) Alignment of the models of PF pair A12/A13 from the doublet (blue) and sarkosyl A-tubule (green) based on the tubulin unit of PF-A12 reveals ∼3° difference in rotation (black arrow). (H) The model of PFs A12/A13 from the doublet with the vectors (red) of the displacement of Cα compared to the sarkosyl A-tubule model. Nucleotides, yellow.