The paclitaxel site in tubulin probed by site-directed mutagenesis of Saccharomyces cerevisiae beta-tubulin.

Previously, we created a paclitaxel-sensitive strain of Saccharomyces cerevisiae by mutating five amino acid residues in beta-tubulin in a strain that has a decreased level of the ABC multidrug transporters. We have used site-directed mutagenesis to examine the relative importance of the five residues in determining sensitivity of this strain to paclitaxel. We found that the change at position 19 from K (brain beta-tubulin) to A (yeast beta-tubulin) and at position 227 from H (brain beta-tubulin) to N (yeast beta-tubulin) had no effect on the activity of paclitaxel. On the other hand, the changes V23T, D26G and F270Y, drastically reduced sensitivity of AD1-8-tax to paclitaxel. Molecular modeling and computational studies were used to explain the results.