mikrotubulusten

Mikrotubulusten are a key component of the cytoskeleton in most eukaryotic cells. They are polymers of tubulin dimers, each consisting of alpha- and beta-tubulin, that assemble into hollow tubes with a diameter of about 25 nanometers. Microtubules exhibit polarity, with a rapidly growing plus end and a slower minus end, which is often anchored at microtubule organizing centers such as the centrosome in animal cells.

Dynamic instability drives their remodeling: GTP-bound tubulin adds to the plus end; after incorporation, GTP is hydrolyzed to GDP, making the lattice less stable. When the GTP cap is lost, rapid depolymerization (catastrophe) can occur, followed by rescue events that restore growth. This dynamic behavior allows cells to reorganize their cytoskeleton quickly in response to cues.

Microtubules provide tracks for motor proteins, mainly kinesin and dynein, enabling polarized transport of organelles, vesicles, and macromolecules. They form the mitotic spindle during cell division, helping to separate chromosomes, and they are essential components of cilia and flagella, where they organize the axoneme. In neurons, long microtubules support axonal transport and shape.

Regulation occurs through microtubule-associated proteins (MAPs) that stabilize or destabilize filaments, severing enzymes, and post-translational modifications of tubulin. Pharmacological agents that stabilize (taxanes) or destabilize (vinca alkaloids, colchicine) microtubules are widely used in research and medicine, notably in cancer therapy. Abnormal microtubule dynamics are associated with neurodegenerative diseases and developmental disorders.