Featured Research

from universities, journals, and other organizations

New details on microtubules and how the anti-cancer drug Taxol works

Date:
May 22, 2014
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
Images of microtubule assembly and disassembly have been produced by researchers at the unprecedented resolution of 5 angstroms, providing new insight into the success of the anti-cancer drug Taxol and pointing the way to possible improvements. "This is the first experimental demonstration of the link between nucleotide state and tubulin conformation within the microtubules and, by extension, the relationship between tubulin conformation and the transition from assembled to disassembled microtubule structure," says a biophysicist on the study.

The most detailed look ever at the assembly and disassembly of microtubules, tiny fibers of tubulin protein that play a crucial role in cell division, provides new insight into the success of the anti-cancer drug Taxol.
Credit: Image courtesy of DOE/Lawrence Berkeley National Laboratory

A pathway to the design of even more effective versions of the powerful anti-cancer drug Taxol has been opened with the most detailed look ever at the assembly and disassembly of microtubules, tiny fibers of tubulin protein that form the cytoskeletons of living cells and play a crucial role in mitosis. Through a combination of high-resolution cryo-electron microscopy (cryo-EM) and new methodology for image analysis and structure interpretation, researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have produced images of microtubule assembly and disassembly at the unprecedented resolution of 5 angstroms (). Among other insights, these observations provide the first explanation of Taxol's success as a cancer chemotherapy agent.

"This is the first experimental demonstration of the link between nucleotide state and tubulin conformation within the microtubules and, by extension, the relationship between tubulin conformation and the transition from assembled to disassembled microtubule structure," says Eva Nogales, a biophysicist with Berkeley Lab's Life Sciences Division who led this research. "We now have a clear understanding of how hydrolysis of guanosine triphosphate (GTP) leads to microtubule destabilization and how Taxol works to inhibit this activity."

Nogales, who is also a professor of biophysics and structural biology at UC Berkeley, as well as an investigator with the Howard Hughes Medical Institute, is the corresponding author of a paper describing this research in the journal Cell. The paper is entitled "High resolution αβ microtubule structures reveal the structural transitions in tubulin upon GTP hydrolysis." Co-authors are Gregory Alushin, Gabriel Lander, Elizabeth Kellogg, Rui Zhang and David Baker.

During mitosis, the process by which a dividing cell duplicates its chromosomes and distributes them between two daughter cells, microtubules disassemble and reform into spindles across which the duplicate sets of chromosomes migrate. For chromosome migration to occur, the microtubules attached to them must disassemble, carrying the chromosomes in the process. The crucial ability of microtubules to transition from a rigid polymerized or "assembled" state to a flexible depolymerized or "disassembled" state -- called "dynamic instability" -- is driven by GTP hydrolysis in the microtubule lattice. Taxol prevents or dramatically slows down the unchecked cell division that is cancer by binding to a microtubule in such a manner as to block the effects of hydrolysis. However, until now the atomic details as to how microtubules transition from polymerized to depolymerized structures and the role that Taxol can play have been sketchy.

"Uncovering the atomic details of the conformational cycle accompanying polymerization, nucleotide hydrolysis, and depolymerization is essential for a complete description of microtubule dynamics," Nogales says. "Such details should significantly aid in improving the potency and selectivity of existing anti-cancer drugs, as well as facilitate the development of novel agents."

To find these details, Nogales, an expert in electron microscopy and image analysis and a leading authority on the structure and dynamics of microtubules, employed cryo-EM, in which protein samples are flash-frozen at liquid nitrogen temperatures to preserve their natural structure. Using an FEI 300 kV Titan cryo-EM from the laboratory of Robert Glaeser, she and her colleagues generated cryo-EM reconstructions of tubulin proteins whose structures were either stabilized by GMPCPP, a GTP analogue, or were unstable and bound to guanosine diphosphate (GDP), or were bound to GDP but stabilized by the presence of Taxol.

The tubulin protein is a heterodimer consisting of alpha (α) and beta (β) monomer subunits. It features two guanine nucleotide binding sites, an "N-site" on the α-tubulin that is buried, and an "E-site" on the β-tubulin that is exposed when the tubulin is depolymerized. Previous microtubule reconstruction studies were unable to distinguish the highly similar α-tubulin and β-tubulin from each other.

"To be able to distinguish the α-tubulin from the β-tubulin, we had to resolve our images at better than 8 , which most prior cryo-EM studies were unable to do," Nogales says. "For that, we marked the subunits with kinesin, a protein motor that distinguishes between α- and β-tubulin."

Nogales and her colleagues found that GTP hydrolysis and the release of the phosphate (GTP becomes GDP) leads to a compaction of the E-site and a rearrangement of the α-tubulin monomer that generates a strain on the microtubule that destabilizes its structure. Taxol binding leads to a reversal of this E-site compaction and α-tubulin rearrangement that restores structural stabilization.

"Remarkably, Taxol binding globally reverses the majority of the conformational changes we observe when comparing the GMPCPP and GDP states," Nogales says. "We propose that GTP hydrolysis leads to conformational strain in the microtubule that would be released by bending during depolymerization. This model is consistent with the changes we observe upon taxol binding, which dramatically stabilizes the microtubule lattice. Our analysis supports a model in which microtubule-stabilizing agents like Taxol modulate conformational strain and longitudinal contacts in the microtubule lattice."


Story Source:

The above story is based on materials provided by DOE/Lawrence Berkeley National Laboratory. The original article was written by Lynn Yarris. Note: Materials may be edited for content and length.


Journal Reference:

  1. Gregory Alushin, Gabriel Lander, Elizabeth Kellogg, Rui Zhang and David Baker. High resolution αβ microtubule structures reveal the structural transitions in tubulin upon GTP hydrolysis. Cell, May 2014

Cite This Page:

DOE/Lawrence Berkeley National Laboratory. "New details on microtubules and how the anti-cancer drug Taxol works." ScienceDaily. ScienceDaily, 22 May 2014. <www.sciencedaily.com/releases/2014/05/140522133406.htm>.
DOE/Lawrence Berkeley National Laboratory. (2014, May 22). New details on microtubules and how the anti-cancer drug Taxol works. ScienceDaily. Retrieved August 23, 2014 from www.sciencedaily.com/releases/2014/05/140522133406.htm
DOE/Lawrence Berkeley National Laboratory. "New details on microtubules and how the anti-cancer drug Taxol works." ScienceDaily. www.sciencedaily.com/releases/2014/05/140522133406.htm (accessed August 23, 2014).

Share This




More Matter & Energy News

Saturday, August 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Is It a Plane? No, It's a Hoverbike

Is It a Plane? No, It's a Hoverbike

Reuters - Business Video Online (Aug. 22, 2014) UK-based Malloy Aeronautics is preparing to test a manned quadcopter capable of out-manouvering a helicopter and presenting a new paradigm for aerial vehicles. A 1/3-sized scale model is already gaining popularity with drone enthusiasts around the world, with the full-sized manned model expected to take flight in the near future. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Coal Gas Boom in China Holds Climate Risks

Coal Gas Boom in China Holds Climate Risks

AP (Aug. 22, 2014) China's energy revolution could do more harm than good for the environment, despite the country's commitment to reducing pollution and curbing its carbon emissions. (Aug. 22) Video provided by AP
Powered by NewsLook.com
Former TSA X-Ray Scanners Easily Tricked To Miss Weapons

Former TSA X-Ray Scanners Easily Tricked To Miss Weapons

Newsy (Aug. 21, 2014) Researchers found the scanners could be duped simply by placing a weapon off to the side of the body or encasing it under a plastic shield. Video provided by Newsy
Powered by NewsLook.com
Flower Power! Dandelions Make Car Tires?

Flower Power! Dandelions Make Car Tires?

Reuters - Business Video Online (Aug. 20, 2014) Forget rolling on rubber, could car drivers soon be traveling on tires made from dandelions? Teams of scientists are racing to breed a type of the yellow flower whose taproot has a milky fluid with tire-grade rubber particles in it. As Joanna Partridge reports, global tire makers are investing millions in research into a new tire source. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins