proteinfilament

Protein filaments are long, threadlike polymers formed by the self-assembly of protein subunits into extended filaments. They are central components of the cytoskeleton in many cells, providing structural support, organizing the interior, and serving as tracks for movement. The major classes in eukaryotes are actin filaments (microfilaments), microtubules, and intermediate filaments, each built from different protein families. Bacterial cells also possess actin-like and tubulin-like filaments that organize cell shape and division.

Actin filaments are helical polymers of actin that assemble in an ATP-dependent manner, with distinct plus and minus ends that influence growth rates. Microtubules are hollow tubes assembled from alpha- and beta-tubulin dimers bound to GTP; they undergo dynamic instability with rapid growth and shrinkage. Intermediate filaments are more stable, forming durable networks from diverse proteins such as keratins, vimentin, and lamins, and they primarily provide mechanical resilience.

Filament dynamics are regulated by numerous actin- and tubulin-binding proteins, including capping, severing, crosslinking, and motor-associated factors. Molecular motors such as myosin move along actin filaments, while kinesin and dynein move along microtubules to transport cargos and organize cellular components.

Filaments contribute to cell shape, mechanical strength, intracellular organization, and processes such as vesicle transport, cell adhesion, and chromosome segregation during mitosis and meiosis. Their assembly and disassembly respond to signaling cues, enabling rapid changes in cell polarity and motility. Disruptions in filament networks are linked to a variety of diseases, including cardiomyopathies, neurodegenerative disorders, and skin diseases.