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A GDP-bound tubulin subunit at the tip of a microtubule will fall off, though a GDP-bound tubulin in the middle of a microtubule cannot spontaneously pop out.
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GDP-bound and tubulin
* For example, the cancer-fighting taxane class of drugs paclitaxel and docetaxel block dynamic instability by stabilizing GDP-bound tubulin in the microtubule.
GDP-bound and subunit
PDE γ subunit affinity for GDP-bound T < sub > α </ sub >, however, seems to be about 100-fold smaller than for GTP-bound T < sub > α </ sub >.
GDP-bound and fall
This job seems to fall to the T < sub > βγ </ sub > to keep the GDP-bound T < sub > α </ sub > bound in the form of holotransducin.
GDP-bound and off
Toggling the switch is performed by the unidirectional change of the GTPase from the active, GTP-bound form to the inactive, GDP-bound form by hydrolysis of the GTP through intrinsic GTPase-activity, effectively switching the GTPase off.
Since the GDP-bound form is " off " or " inactive " for signaling, GTPase Activating Protein inactivates Ras by activating its GTPase activity.
In the GDP-bound state, the G proteins are subsequently “ turned off ”; in other words, they are inactivated and can no longer bind their targets.
GDP-bound and .
Hence, activation and deactivation of Ras and other small G proteins are controlled by cycling between the active GTP-bound and inactive GDP-bound forms.
Although the traditional mechanism involves activation of PDE by GTP-bound T < sub > α </ sub >, GDP-bound T < sub > α </ sub > has also been demonstrated to have the ability to activate PDE.
In order to prevent activation of PDE in the dark, the concentration of GDP-bound T < sub > α </ sub > should be kept to a minimum.
The GTPase Sar1p is a protein that hydrolyzes GTP and acts like a molecular " switch " that flips between an activated and membrane embedded GTP-bound form, and inactive and soluble GDP-bound form.
Inactive GDP-bound Sar1p is attracted to the cytosolic side of the endoplasmic reticulum ( ER ) membrane by Sec12p.
ARF cycles between GTP and GDP-bound conformations.
Once in the GDP-bound conformation, ARF converts to a less hydrophobic conformation and dissociates from the membrane.
GDP-bound Sar1 interacts with the membrane-bound exchange factor Sec12 and exchanges its bound GDP for GTP.
REPs carry only the GDP-bound form of Rab, and Rab effectors, proteins with which Rab interacts and through which it functions, only bind the GTP-bound form of Rab.
A GDP dissociation inhbitor ( GDI ) binds the prenyl groups of the inactive, GDP-bound form of Rab, inhibits the exchange of GDP for GTP ( which would reactivate the Rab ) and delivers Rab to its original membrane.
tubulin and subunit
Tubulin polymerizes end to end with the α subunit of one tubulin dimer contacting the β subunit of the next.
y-tubulin is a protein located at the centrosome that nucleates the microtubules by interacting with the tubulin monomer subunit in the microtubule at the minus end.
A tubulin acetyltransferase is located in the axoneme, and acetylates the α-tubulin subunit in an assembled microtubule.
tubulin and at
Since tubulin adds onto the end of the microtubule only in the GTP-bound state, there is a cap of GTP-bound tubulin at the tip of the microtubule, protecting it from disassembly.
* CEP41 is mutated in Joubert syndrome and is required for tubulin glutamylation at the cilium.
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.
Some are straightforward and static, such as the pattern of tubulin, which is expressed in all cells at all times in life.
Because of dynamic instability, some individual microtubules that are not stabilized are at risk of collapse ( or “ catastrophe ” as Kirschner named it ), allowing re-use of the tubulin monomers.
tubulin and tip
The tip is surrounded by a band of microtubules, called the polar ring, and among the Conoidasida there is also a funnel of tubulin proteins called the conoid.
GTP-bound tubulin can begin adding to the tip of the microtubule again, providing a new cap and protecting the microtubule from shrinking.
tubulin and microtubule
This complex acts as a scaffold for α / β tubulin dimers to begin polymerization ; it acts as a cap of the (−) end while microtubule growth continues away from the MTOC in the (+) direction.
Whether the β-tubulin member of the tubulin dimer is bound to GTP or GDP influences the stability of the dimer in the microtubule.
The anti-gout agent colchicine binds to tubulin and inhibits microtubule formation, arresting neutrophil motility and decreasing inflammation.
In the gel state, it was further hypothesized that the water electrical dipoles are oriented in the same direction, along the outer edge of the microtubule tubulin subunits.
This binding can occur with either polymerized or depolymerized tubulin, and in most cases leads to the stabilization of microtubule structure, further encouraging polymerization.
A single study has been suggested that MAP2 and tau bind on the inner microtubule surface on same site in tubulin monomers as the drug Taxol which is used in treating cancer.
tubulin and out
Each tubulin also has a tail extending out from the microtubules, which is negatively charged, and therefore attracts positively charged ions.
tubulin and .
Antiproliferative agents that target tubulin with β-lactams in their structure have also been reported.
These cylindrical polymers of tubulin can grow as long as 25 micrometers and are highly dynamic.
The lateral association of the protofilaments generates an imperfect helix with one turn of the helix containing 13 tubulin dimers, each from a different protofilament.
Note that prokaryotes do not possess tubulin or microtubules.
Contained within the MTOC is another type of tubulin, γ-tubulin, which is distinct from the α and β subunits, which compose the microtubules themselves.
During polymerization, both the α-and β-subunits of the tubulin dimer are bound to a molecule of GTP.
* Nocodazole, vincristine, and Colchicine have the opposite effect, blocking the polymerization of tubulin into microtubules.
This change may make the NPC more permeable to enzymes involved in the degradation of the NE such as cytoplasmic tubulin, as well as allowing the entry of key mitotic regulator proteins.
This remodelling seems to allow the proteins complex cdc2 / cyclinB enter the nucleus as well as many other proteins such as soluble tubulin.
Most structural proteins are fibrous proteins ; for example, actin and tubulin are globular and soluble as monomers, but polymerize to form long, stiff fibers that make up the cytoskeleton, which allows the cell to maintain its shape and size.
The drug functions by binding to tubulin in the worms ' intestinal cells and body-wall muscles.
These models argue that cilia developed from pre-existing components of the eukaryotic cytoskeleton ( which has tubulin and dynein also used for other functions ) as an extension of the mitotic spindle apparatus.
Long-standing suspicions that tubulin was homologous to FtsZ ( based on very weak sequence similarity and some behavioral similarities ) were confirmed in 1998 by the independent resolution of the 3-dimensional structures of the two proteins.
Microtubules are hollow cylinders about 23 nm in diameter ( lumen = approximately 15 nm in diameter ), most commonly comprising 13 protofilaments which, in turn, are polymers of alpha and beta tubulin.
*** polyglutamylation, covalent linkage of glutamic acid residues to the N-terminus of tubulin and some other proteins.
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