profilines

Profilines, also called profilin proteins, are a family of small, ubiquitously expressed actin-binding proteins found in most eukaryotic cells. They play a central role in regulating the actin cytoskeleton, influencing cell shape, migration, and division by modulating actin filament assembly and turnover.

Molecular function and interactions: Profilins bind actin monomers (G-actin) with relatively high affinity and can sequester them to limit spontaneous nucleation of filaments. They also facilitate actin polymerization at existing filament ends in conjunction with actin-assembly factors such as formins and Ena/VASP proteins, often delivering profilin-bound actin to growing filaments. In addition, profilins bind poly-L-proline-rich sequences found in various partner proteins, coupling signaling and membrane-associated processes to cytoskeletal rearrangements. Lipid interactions, notably with phosphatidylinositol 4,5-bisphosphate (PIP2), can regulate profilin localization and activity at membranes.

Distribution and diversity: Vertebrates typically express several profilin isoforms (for example PFN1 and PFN2 in humans) with tissue-specific expression patterns, while other organisms may have broader or divergent profilin families. In plants and fungi, profilins contribute to processes such as pollen tube guidance and endocytosis, reflecting conserved yet adaptable roles in actin regulation.

Clinical and research relevance: Profilins are widely used as model proteins for studying actin dynamics, cytoskeletal control, and cell motility. Dysregulation or mutations in profilin genes, such as PFN1, have been linked to disease contexts including neurodegenerative conditions and cancer, highlighting their importance for normal cellular function.