jp7b01057_si_001.pdf (674.32 kB)
Structure of Dynamic, Taxol-Stabilized, and GMPPCP-Stabilized Microtubule
journal contribution
posted on 2017-08-18, 00:00 authored by Avi Ginsburg, Asaf Shemesh, Abigail Millgram, Raviv Dharan, Yael Levi-Kalisman, Israel Ringel, Uri RavivMicrotubule (MT)
is made of αβ-tubulin
heterodimers that dynamically assemble into a hollow nanotube composed
of straight protofilaments. MT dynamics is facilitated by hydrolysis
of guanosine-5′-triphosphate (GTP) and can be inhibited by
either anticancer agents like taxol or the nonhydrolyzable GTP analogues
like GMPPCP. Using high-resolution synchrotron X-ray scattering, we
have measured and analyzed the scattering curves from solutions of
dynamic MT (in other words, in the presence of excess GTP and free
of dynamic-inhibiting agents) and examined the effect of two MT stabilizers:
taxol and GMPPCP. Previously, we have analyzed the structure of dynamic
MT by docking the atomic model of tubulin dimer onto a 3-start left
handed helical lattice, derived from the PDB ID 3J6F. 3J6F corresponds to a
MT with 14 protofilaments. In this paper, we took into account the
possibility of having MT structures containing between 12 and 15 protofilaments.
MTs with 12 protofilaments were never observed. We determined the
radii, the pitch, and the distribution of protofilament number that
best fit the scattering data from dynamic MT or stabilized MT by taxol
or GMPPCP. We found that the protofilament number distribution shifted
when the MT was stabilized. Taxol increased the mass fraction of MT
with 13 protofilaments and decreased the mass fraction of MT with
14 protofilaments. GMPPCP reduced the mass fraction of MT with 15
protofilaments and increased the mass fraction of MT with 14 protofilaments.
The pitch, however, remained unchanged regardless of whether the MT
was dynamic or stabilized. Higher tubulin concentrations increased
the fraction of dynamic MT with 14 protofilaments.