Fig. 4.
Quantification of GMPCPP-microtubule geometries reveals that distortions are irregular, common, and can be bimodally distributed. (A) Illustration of the expected rotation difference between neighboring filaments in a symmetric microtubule (Top, ΔφE) and in a distorted microtubule (Bottom, ΔφM). The difference between the symmetric and measured rotational difference is the distortion (ΔφD). (B) The estimated wall angle distortion (ΔφD) as a function of the protofilament number n for a representative microtubule, plotted separately for each of seven consecutive axial repeats. Scale bar for the y axis (ΔφD), identical for each graph, is shown on the Left. (C) Histogram of nonseam (Top) and seam (Bottom) wall angles for 14-protofilament GMPCPP-stabilized microtubules. (D) Particles corresponding to the highlighted wall angles in C were selectively reconstructed, yielding angles of 21° and 31° between the target protofilaments. See also SI Appendix, Fig. S3. (E) Histogram of nonseam (Top) and seam (Bottom) wall angles for 13-protofilament GMPCPP-stabilized microtubules. A double Gaussian curve was fit to all displayed distributions, except the 14-protofilament seam distribution, which was fit by a single Gaussian function. The mean and relative population of each Gaussian distribution is noted by the respective peak. The distance of each mean from the symmetric wall angle (ΔφE, denoted by the solid black line) is also indicated above each peak. (F) The 13-protofilament seam particles corresponding to the low and high angular components of the distribution (highlighted in E in yellow and cyan) were separated and selectively reconstructed.