Fibrillen

Fibrillen, or fibrils, are slender, thread-like structures found in cells, tissues, and extracellular matrices. They are typically formed by the polymerization of protein subunits, though some fibrils in plants or minerals can have different compositions. Fibrils are smaller than fibers and commonly range from a few nanometers to several hundred nanometers in diameter. Their arrangement and cross-linking give rise to mechanical strength, shape, and organization within biological systems.

Common examples include cytoskeletal and extracellular fibrils. Actin filaments, about 7 nanometers in diameter, are key components of the cytoskeleton that enable cell movement and shape changes. Collagen fibrils, found in connective tissue, have diameters from tens to hundreds of nanometers and exhibit a characteristic staggered arrangement of collagen molecules that provides tensile strength; they show a regular banding pattern known as the D-period. Neurofibrils are networks of intermediate filament fibrils within neurons, contributing to structural support and axonal transport.

Amyloid fibrils are a distinct class of protein fibrils formed when normally soluble proteins misfold and aggregate into cross-beta-sheet rich structures. These fibrils accumulate in tissues in several diseases, including Alzheimer’s disease and some prion disorders, and are a focus of diagnostic staining and imaging studies.

Fibrillen also occur in plants and fungi as cellulose or chitin fibrils in cell walls and structures. In summary, fibrils are versatile, nanoscale to submicron polymers that provide structural integrity and organization across biological systems.