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Microtubules, a major component of the eukaryotic cytoskeleton, comprise an effective, validated target for cancer chemotherapeutic drugs. One class of drugs, known as microtubule stabilizing agents, bind to microtubule polymers and stabilize them against depolymerization. The prototype of this class of drugs is Taxol®, but other natural products have a similar mechanism of action. Taxol is an effective chemotherapeutic drug used extensively in the treatment of human ovarian, breast and lung carcinomas. This presentation will highlight the fascinating history of the development of Taxol, from the tree bark to the bedside.
Microtubules are a family of complex proteins, composed of α- and β- tubulin dimers. There are eight α-tubulin isotypes and seven β-tubulin isotypes, products of distinct genes whose proteins display extensive molecular heterogeneity at their C-terminal ends. Numerous posttranslational modifications occur primarily within the C-terminal 20 amino acids of the α- and β- subunits. The C-terminal isotype sequence conservation, and their differential tissue expression, strongly implies a functional significance to the tubulin isotypes. Our laboratory has developed proteomic methods, including high-resolution isoelectrofocusing, CNBr cleavage and mass spectrometry that permit us to determine the isotype content and posttranslational modifications of tubulin in cells and tissues.
Although electron crystallography and photoaffinity labeling experiments have revealed that the binding site for Taxol is in a hydrophobic pocket in β-tubulin, little was known about the effects of this drug on the conformation of the entire microtubule system. Research from our laboratory utilizing hydrogen-deuterium exchange (HDX) has provided new information on the conformation of microtubules upon Taxol binding.