Paclitaxel hyperstabilizes polymerized microtubules (made up of alpha- and beta- tubulin)

Beta-Tubulin is a subunit of tubulin. Tubulin is one of several members of a small family of globular proteins. It is the major constituent of microtubules. There are two of most common members of the tubulin family: alpha-tubulin and beta-tubulin, and together their dimers form microtubules. (origene.com)

Vinca and plant alkaloids bind B-tubulin, which inhibits the formation or disassembly or microtubules, respectively.