Profiline

Profiline, commonly referred to as profilin in scientific literature, is a small cytosolic actin-binding protein that regulates actin dynamics in eukaryotic cells. It is a member of the profilin family and is widely distributed across eukaryotes, including animals, plants, and fungi. In humans, two gene variants, PFN1 and PFN2, encode profilin-1 and profilin-2, respectively. The proteins are compact, with a molecular weight in the low tens of kilodaltons, and they share a conserved structure that supports interactions with actin monomers and several regulatory partners.

Functionally, profilin binds actin monomers (G-actin) and promotes nucleotide exchange on the bound actin, enabling efficient cycling between ADP- and ATP-bound forms. By delivering actin monomers to the growing ends of filaments in cooperation with actin-assembly factors such as formins and Ena/VASP proteins, profilin facilitates controlled filament elongation while reducing spontaneous nucleation. Profilin also interacts with polyproline-rich sequences in a variety of actin-regulatory proteins, linking signaling pathways to cytoskeletal remodeling. Additionally, profilin can associate with phosphoinositides in cellular membranes, connecting membrane signals to cytoskeletal changes.

Biological roles of profilin encompass cell migration, polarization, endocytosis, and development. In the nervous system, profilin influences processes related to axon guidance and synaptic organization. Clinically, mutations in PFN1 have been linked to familial amyotrophic lateral sclerosis (ALS), and aberrant profilin expression has been observed in certain cancers and neurodegenerative contexts, though effects are context-dependent.

History and discovery place profilin among early-described actin-binding proteins identified in the 1980s. See also actin, formins, Ena/VASP, and profilin-like proteins.