Fig. 4.

Class III β-tubulin subunit contains unique residue 218 (T218A) in the leucine cluster and residue 275 (S275A) in the M-loop. β-Tubulin subunit (gray) in complex with Taxol (stick representation) and GDP (green). M-loop (yellow) is involved in both Taxol binding and interaction with lateral β-tubulin in the microtubule. Four Cα atoms (CA, red spheres) are used to define the binding pocket dimensions. T218 and S275, which are alanines in β-tubulin isotype III, have negligible interactions with Taxol.