profilinbound

Profilinbound is a term sometimes used to describe the state in which profilin is bound to an actin monomer, forming a profilin–actin complex. The expression is not a standard nomenclature in all literature, but the concept of profilin bound to actin is central to understanding how actin monomers are recycled and delivered for filament growth in eukaryotic cells.

Biochemically, profilin binds G-actin with high affinity and largely sequesters actin monomers to prevent spontaneous nucleation of new filaments. In this complex, profilin promotes the exchange of ADP for ATP on the actin monomer, priming it for rapid incorporation into filaments. The profilin–actin complex remains competent for elongation at the growing (barbed) end, particularly when actin assembly is facilitated by specialized nucleators such as formins or Ena/VASP proteins.

Profilin interacts with poly-L-proline motifs found in many actin-regulatory proteins, providing a molecular link between signaling pathways and cytoskeletal assembly. It also associates with phosphoinositides, notably PIP2, which helps localize profilin–actin complexes to membranes and coordinate actin remodeling with membrane traffic and signaling processes.

Biologically, profilinbound contributes to controlled cytoskeletal dynamics essential for processes such as cell migration, endocytosis, and cytokinesis. Its activity is modulated by isoforms and cellular context, with different organisms possessing profilin variants that can influence actin turnover and organization. In human biology, profilin A and B (PFN1 and PFN2) are studied for their roles in health and disease, including neurobiology and cancer.

See also: profilin, actin, formins, Ena/VASP, Arp2/3, PIP2.