Plastins

Plastins, also known as fimbrins, are a family of actin-binding proteins that organize the cytoskeleton by cross-linking actin filaments into tight, parallel bundles. In vertebrates, three plastin isoforms have been described: L-plastin (PLS1), T-plastin (PLST), and I-plastin (PLS3), encoded by the genes PLS1, PLS2, and PLS3 respectively. Structurally, plastins contain two actin-binding domains (ABD1 and ABD2), each consisting of calponin-homology domains, arranged to bridge actin filaments. A central regulatory region may include calcium-binding motifs in some isoforms, allowing calcium-dependent regulation of bundling activity. Phosphorylation and interactions with other cytoskeletal proteins can also influence localization and activity.

Expression and localization: L-plastin is primarily expressed in hematopoietic cells and some other tissues; T-plastin is found in a broad range of solid tissues; I-plastin is enriched in cells with specialized microvilli, such as the intestinal epithelium and some sensory cells.

Function: Plastins organize actin networks by bundling filaments, contributing to cell shape, cortical stability, and mechanical resilience. They are important for the formation of specialized structures such as microvilli and stereocilia and participate in processes that require dynamic actin remodeling, including cell migration and immune cell function.

Evolution and research: Plastins belong to the fimbrin/plastin family of actin-bundling proteins and are conserved across eukaryotes. In humans, the three gene products have distinct expression patterns and roles, with ongoing research into their regulation, interactions, and involvement in disease.