S. Rao et al., 3'-(P-AZIDOBENZAMIDO)TAXOL PHOTOLABELS THE N-TERMINAL 31 AMINO-ACIDS OF BETA-TUBULIN, The Journal of biological chemistry, 269(5), 1994, pp. 3132-3134
Taxol possesses an unusual chemical structure, a unique mechanism of a
ction, and demonstrated activity in human malignancies. It is the only
antitumor agent that has a binding site on the microtubule polymer. T
he interaction of Taxol with the microtubule polymer results in the fo
rmation of stable bundles of cellular microtubules that are resistant
to depolymerization. Although it has become evident that the microtubu
le, specifically beta-tubulin, is the target for Taxol, no information
is available on the binding site for the drug. In this report, we dem
onstrate that 3'-(p-azidobenzamido)taxol, an analogue with similar bio
logical activities as Taxol, covalently binds to the N-terminal domain
of beta-tubulin after irradiation of the microtubule-drug complex. Ta
xol competes with [H-3]3'-(p-azidobenzamido)taxol binding, suggesting
that the photoaffinity analog and Taxol are binding at the same or ove
rlapping sites. Formic acid cleavage of [H-3]3'-(p-azidobenzamido)taxo
l-photolabeled beta-tubulin and subsequent protein sequence and mass a
nalyses have identified the N-terminal 31 amino acids as the major sit
e for [H-3]3'-(p-azidobenzamido)taxol photoincorporation.