Surface map of conserved residues in all human β-tubulin isotypes. A solvent accessible surface was drawn onto the α/β tubulin heterodimer obtained by Löwe et al. . An alignment of all human β-tubulin isotypes provided a score of overall homology at each amino acid position from 0–100%. This figure shows an α/β tubulin heterodimer, with the α-tubulin surface colored white and the β-tubulin surface colored blue and red. Individual surface residues within the β-tubulin monomer were colored to indicate the overall degree of homology ranging from light blue for 100% to bright red for 0–9%, with shades of red from brighter to paler illustrating those residues that are 10–39%, 40–79% and 70–99% homologous respectively. Two representations illustrate the paclitaxel bound interior of the microtubule and a 90° rotation about the y-axis to show the exterior of the microtubule. Figure reproduced from Huzil et al. .