Abstract
Microtubules are found in all eukaryotes and are built from alphabeta-tubulin heterodimers. The alpha-tubulins and beta-tubulins are among the most highly conserved eukaryotic proteins. Other members of the tubulin family have come to light recently and, like gamma-tubulin, appear to play roles in microtubule nucleation and assembly. Microtubule assembly is accompanied by hydrolysis of GTP associated with beta-tubulin so that microtubules consist principally of "GDP-tubulin" stabilized by a short "GTP cap." Microtubules are polar, cylindrical structures some 25 nm in diameter. Protofilaments made from tubulin heterodimers run lengthwise along the microtubule wall with the beta-tubulin subunit at the microtubule plus end. The crystallographic structures of tubulins are essential to understand in detail microtubule architecture and interactions with stabilizing and destabilizing drugs and proteins.