Fimbrin

Fimbrin is a protein that plays a crucial role in the organization of actin filaments within cells. It belongs to the plastin family, which consists of actin-binding proteins involved in the formation of tight actin bundles. Fimbrin is particularly important in the formation of microvilli, finger-like protrusions on the surface of cells that increase the surface area for absorption and secretion. This protein is encoded by the gene PLS1 in humans.

Function

Fimbrin binds to actin filaments and holds them together in a parallel fashion, facilitating the tight packing of filaments necessary for the structural integrity of microvilli. By cross-linking actin filaments, fimbrin plays a vital role in the maintenance of cell shape, cell motility, and the stabilization of cell junctions. It is also involved in various cellular processes, including signal transduction, cell division, and the regulation of gene expression.

Structure

Fimbrin contains two actin-binding domains, which allow it to bind simultaneously to two actin filaments, and a calcium-binding domain, which regulates its actin-binding activity. The precise arrangement of these domains enables fimbrin to cross-link actin filaments with a specific orientation and spacing, critical for the formation of tightly packed bundles.

Clinical Significance

Alterations in fimbrin expression or function have been implicated in several diseases. For example, abnormalities in microvilli formation due to fimbrin dysfunction can lead to microvillous inclusion disease, a rare and severe disorder affecting intestinal absorption. Furthermore, changes in fimbrin expression levels have been observed in various cancers, suggesting a role in tumorigenesis and metastasis. Research into fimbrin and its interactions with actin filaments continues to provide insights into the molecular mechanisms underlying these conditions.

See Also

• Actin
• Microvilli
• Plastin
• Cell biology