Twelve protofilament taxol‐induced microtubules assembled from purified tublin. A synchrotron X‐ray scattering study in comparison with glycerol‐ and map‐induced microtubules

The X‐ray solution scattering profiles of taxol microtubules made of purified tubulin and control microtubules, assembled either from purified tubulin in glycerol buffer (a non‐specific enhancer of the polymerization of tubulin) or from microtubule protein (a preparation containing tubulin plus microtubule associated proteins), were obtained to 3.3 nm resolution. These profiles show features of the microtubule wall structure which had not been observed in solution before. Comparison of the different profiles indicated that the structure of the microtubule wall is very similar in the three types of microtubules to the resolution of the measurements, however the mean diameter of the taxol microtubules is smaller than that of the control microtubules, by approximately one protofilament less. Actually, only 12 protofilament computer models of microtubules could fit the position of the maxima in the experimental scattering profile of the taxol microtubules. Having only 12 protofilaments implies a discontinuity...