microtubule nucleator activity

Definition

Target type: molecularfunction

The action of a molecule that provides a shape mimicking the end of a microtubule to seed the formation of a new microtubule via self-assembly. [PMID:20631709, PMID:21993292]

Microtubule nucleator activity is a fundamental process in cell biology, essential for the formation and organization of microtubule networks. Microtubules, long, cylindrical polymers composed of α- and β-tubulin dimers, play crucial roles in diverse cellular functions, including cell division, intracellular transport, and cell shape maintenance. Microtubule nucleators are specialized protein complexes that initiate the assembly of microtubules by providing a platform for tubulin dimer binding and polymerization. This activity is characterized by the ability to promote the formation of new microtubule minus ends, which serve as the nucleation sites for microtubule elongation. There are various mechanisms employed by different microtubule nucleators, each contributing to distinct aspects of microtubule assembly and regulation. These include:

1. **γ-tubulin ring complex (γ-TuRC):** The most well-characterized microtubule nucleator in eukaryotic cells, γ-TuRC assembles into a ring-shaped structure that provides a template for the initial tubulin dimer binding. It plays a crucial role in microtubule nucleation at the centrosomes, the main microtubule organizing centers (MTOCs) in most cells.

2. **Augmin complex:** Augmin is a microtubule nucleator that acts specifically at microtubule plus ends. It recruits γ-TuRC to existing microtubules, promoting the formation of branched microtubule arrays, crucial for spindle formation and chromosome segregation during cell division.

3. **Nucleation-promoting factors (NPFs):** NPFs are a diverse group of proteins that modulate microtubule nucleation by interacting with and regulating γ-TuRC activity. They can either enhance or inhibit γ-TuRC-mediated nucleation, influencing the spatial and temporal control of microtubule formation.

4. **Microtubule-organizing centers (MTOCs):** While not proteins themselves, MTOCs like centrosomes and spindle poles act as platforms that concentrate and organize microtubule nucleators. They create localized environments that promote microtubule nucleation, ensuring the proper spatial organization of microtubule networks.

5. **Microtubule-associated proteins (MAPs):** Certain MAPs, like the XMAP215 family, can directly promote microtubule nucleation by stabilizing the initial tubulin dimer aggregates.

6. **Microtubule-severing proteins:** Proteins like katanin can sever existing microtubules, generating new microtubule minus ends that can serve as nucleation sites for further microtubule assembly.

The precise mechanisms by which these different microtubule nucleators function are actively being investigated. However, their collective activities are essential for the dynamic assembly and organization of microtubule networks, which in turn underpin diverse cellular processes. Understanding the regulation and function of microtubule nucleators is crucial for comprehending cell division, intracellular transport, and the organization of cellular architecture.
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Compounds (1)