This MedLibrary.org supplementary page on Tubulin is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
A Tubulin is one of several members of a small family of globular proteins. The most common members of the tubulin family are α-tubulin and β-tubulin, the proteins that make up microtubules. Each has a molecular weight of approximately 55 kiloDaltons. Microtubules are assembled from dimers of α- and β-tubulin. These subunits are slightly acidic with an isoelectric point between 5.2 and 5.8.
Tubulin was long thought to be specific to eukaryotes. Recently, however, the prokaryotic cell division protein FtsZ was shown to be evolutionarily related to tubulin.citation needed
Contents |
α-tubulin and β-tubulin
To form microtubules, the dimers of α- and β-tubulin bind to GTP and assemble onto the (+) ends of microtubules while in the GTP-bound state. After being incorporated into the microtubule, the bound molecule of GTP will hydrolyse into GDP.
Although both subunits bind GTP, only the β-subunit has GTPase activity; that is, β-tubulin can hydrolyse GTP to GDP whereas α-tubulin cannot. Whether the β-tubulin member of the tubulin dimer is bound to GTP or GDP influences the stability of the dimer in the microtubule.
Dimers bound to GTP tend to assemble into microtubules, while dimers bound to GDP tend to fall apart; thus, this GTP cycle is essential for the dynamic instability of the microtubule.
Class III β-tubulin is a microtubule element expressed exclusively in neurons, and is a popular identifier specific for neurons in nervous tissue.
Katanin is a protein complex that severs β-tubulin, and is necessary for rapid microtubule transport in neurons and in higher plants.
Human α- and β-tubulin subtypes include:
γ-tubulin
γ-tubulin, another member of the tubulin family, is important in the nucleation and polar orientation of microtubules. It is found primarily in centrosomes and spindle pole bodies, since these are the areas of most abundant microtubule nucleation. In these organelles, several γ-tubulin and other protein molecules are found in complexes known as γ-tubulin ring complexes (γ-TuRCs), which chemically mimic the (+) end of a microtubule and thus allow microtubules to bind. γ-tubulin also has been isolated as a dimer and as a part of a γ-tubulin small complex (γTuSC), intermediate in size between the dimer and the γTuRC. γ-tubulin is the best understood mechanism of microtubule nucleation, but certain studies have indicated that certain cells may be able to adapt to its absence, as indicated by mutation and RNAi studies that have inhibited its correct expression.
Human γ-tubulin subtypes include:
δ and ε tubulin
Delta (δ) and epsilon (ε) tubulin have been found to localize at centrioles and may play a role in forming the mitotic spindle during mitosis, though neither is as well-studied as the α- and β- forms.
Human δ- and ε-tubulin subtypes include:
Pharmacology
Tubulins are targets for anticancer drugs like Taxol and the "Vinca alkaloid" drugs such as vinblastine and vincristine. The anti-gout agent colchicine binds to tubulin and inhibits microtubule formation, arresting neutrophil motility and decreasing inflammation. The anti-fungal drug Griseofulvin targets mictotubule formation and has applications in cancer treatment.
See also
External links
|
||||||||||||||||||||
|
||||||||||||||
Wikipedia content modification information:
- This page was last modified on 9 November 2008, at 20:13.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Tubulin".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.