<p>Gelsolin is a cytoplasmic, calcium-regulated, actin-modulating protein that bindsto the barbed ends of actin filaments, preventing monomer exchange (end-blocking orcapping) [<cite idref="PUB00001347"/>]. It can promote nucleation (the assembly ofmonomers into filaments), as well as sever existing filaments. In addition, this proteinbinds with high affinity to fibronectin. Plasma gelsolin and cytoplasmic gelsolin arederived from a single gene by alternate initiation sites and differential splicing.</p><p>Sequence comparisons indicate an evolutionary relationship between gelsolin,villin, fragmin and severin [<cite idref="PUB00003232"/>]. Six large repeating segmentsoccur in gelsolin and villin, and 3 similar segments in severin and fragmin. While themultiple repeats have yet to be related to any known function of the actin-severingproteins, the superfamily appears to have evolved from an ancestral sequence of 120to 130 amino acid residues [<cite idref="PUB00003232"/>].</p> Gelsolin domain