A ribbon diagram based on the 3.7 angstrom resolution model of tubulin developed by Berkeley Lab scientists shows the protein to be a dimer consisting of two monomers that are almost identical in structure. In addition to a nucleotide binding site, each monomer also has two other binding sites, one for proteins, and one for the anti-cancer drug taxol. Tubulin is the protein that polymerizes into long chains or filaments that form microtubules, hollow fibers which serve as a skeletal system for living cells. Microtubules have the ability to shift through various formations which is what enables a cell to undergo mitosis or to regulate intracellular transport. The formation-shifting of microtubules is made possible by the flexibility of tubulin which is why scientists have sought to understand the protein's atomic structure since its discovery in the 1950s.
Cancer occurs when cell division runs amok.
By binding to tubulin and causing the protein to lose its flexibility, taxol prevents a cell from dividing. With better knowledge of tubulin structure and its interaction with taxol, scientists believe that an even more effective anti-cancer drug, one that interacts only with the tubulin of cancerous cells, could be synthesized. The knowledge gained from this model should be of invaluable help in understanding the microtubule system in the cell. The assembly of tubulin and its regulation through dynamic instability results from the fine tuning of the three components. To produce their model, the Berkeley Lab researchers first polymerized tubulin proteins under the same conditions in which microtubules are formed except for the additional presence of zinc.