Profilins are a group of small eukaryotic proteins that bind to monomeric actin (G-actin) in a 1:1 ratio thus preventing the polymerisation of actin into filaments (F-actin). They can also in certain circumstance promote actin polymerisation. Profilins also bind to polyphosphoinositides such as PIP2 []. Other ligands include members of the Ena/VASP and formin families []. Overall sequence similarity among profilin from organisms which belong to different phyla (ranging from fungi to mammals) is low, but the N-terminal region is relatively well conserved. The N-terminal region is thought to be involved in actin binding. Four Profilins have been identified in mammals, PFN1-4. This entry represents Profilin-3 (PFN3), which is mainly expressed in spermatids [, ]. PFN3 has an actin-binding site, but retains only approximately half of the poly-L-proline binding site [].
