Fesselin or avian synaptopodin 2 is a member of the synaptopodin family of
actin binding proteins.
Fesselin promotes
G-actin polymerization and the formation of large actin complexes that can be collected by low-speed centrifugation. Because of the potential role of
fesselin in some
cancers and its effects on actin, we further investigated the effect of
fesselin on actin.
Fesselin initiated actin polymerization under a variety of conditions, including the virtual absence of
salt. Actin filaments formed at low
salt concentrations in the presence of
fesselin were similar to filaments polymerized in the presence of 100 mM KCl. In both cases, the filaments were long and straight with a common orientation. Highly ordered actin bundles formed with increasing times of incubation. Blockers of actin growth at the barbed end (
cytochalasin D and CapZ) did not prevent
fesselin from polymerizing actin. Low concentrations of
fesselin increased the critical concentration of actin. Both observations are consistent with preferential growth at the pointed end of actin filaments. These results indicate a role of
fesselin in organizing cellular actin. These and other results indicate that
fesselin is part of a cellular actin organizing center.