Microtubule: Difference between revisions

Microtubule in vitro assays for motor proteins such as dynein and kinesin are researched by fluorescently tagging a microtubule and fixing either the microtubule or motor proteins to a microscope slide then visualizing the slide with video-enhanced microscopy to record the travel of the microtubule motor proteins. This allows the movement of the motor proteins along the microtubule or the microtubule moving across the motor proteins.<ref>{{cite journal | vauthors = Cooper GM | title = Microtubule Motors and Movements| journal = The Cell: A Molecular Approach. 2nd Edition| access-date = 2019-03-12| date = 2000| url = https://www.ncbi.nlm.nih.gov/books/NBK9833/}}</ref> Consequently, some microtubule processes can be determined by [[kymograph]].<ref>{{cite journal | vauthors = Kapoor V, Hirst WG, Hentschel C, Preibisch S, Reber S | title = MTrack: Automated Detection, Tracking, and Analysis of Dynamic Microtubules | journal = Scientific Reports | volume = 9 | issue = 1 | pages = 3794 | date = March 2019 | pmid = 30846705 | pmc = 6405942 | doi = 10.1038/s41598-018-37767-1 | bibcode = 2019NatSR...9.3794K | doi-access = free }}</ref>

Dynamic instability refers to the coexistence of assembly and disassembly at the ends of a microtubule. The microtubule can dynamically switch between growing and shrinking phases in this region.<ref>{{Cite book | vauthors = Karp G | title = Cell and Molecular Biology: Concepts and Experiments | publisher = John Wiley & Sons | year = 2005 | location = USA | page = [https://archive.org/details/cellmolecularbio04edkarp/page/355 355] | isbn = 978-0-471-46580-5 | url = https://archive.org/details/cellmolecularbio04edkarp/page/355 }}</ref> Tubulin dimers can bind two molecules of GTP, one of which can be hydrolyzed subsequent to assembly. During polymerization, the tubulin dimers are in the [[Guanosine triphosphate|GTP]]-bound state.<ref name="weisenberg" /> The GTP bound to α-tubulin is stable and it plays a structural function in this bound state. However, the GTP bound to β-tubulin may be [[hydrolysis|hydrolyzed]] to [[Guanosine diphosphate|GDP]] shortly after assembly. The assembly properties of GDP-tubulin are different from those of GTP-tubulin, as GDP-tubulin is more prone to depolymerization.<ref>{{cite journal | vauthors = Weisenberg RC, Deery WJ, Dickinson PJ | title = Tubulin-nucleotide interactions during the polymerization and depolymerization of microtubules | journal = Biochemistry | volume = 15 | issue = 19 | pages = 4248–54 | date = September 1976 | pmid = 963034 | doi = 10.1021/bi00664a018 }}</ref> A GDP-bound tubulin subunit at the tip of a microtubule will tend to fall off, although a GDP-bound tubulin in the middle of a microtubule cannot spontaneously pop out of the polymer. Since tubulin adds onto the end of the microtubule in the GTP-bound state, a cap of GTP-bound tubulin is proposed to exist at the tip of the microtubule, protecting it from disassembly. When hydrolysis catches up to the tip of the microtubule, it begins a rapid depolymerization and shrinkage. This switch from growth to shrinking is called a catastrophe. GTP-bound tubulin can begin adding to the tip of the microtubule again, providing a new cap and protecting the microtubule from shrinking. This is referred to as "rescue".<ref name="pmid6504138">{{cite journal | vauthors = Mitchison T, Kirschner M | title = Dynamic instability of microtubule growth | journal = Nature | volume = 312 | issue = 5991 | pages = 237–42 | year = 1984 | pmid = 6504138 | doi = 10.1038/312237a0 | bibcode = 1984Natur.312..237M | s2cid = 30079133 }}</ref>