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Profilin is an actin-binding protein involved in the dynamic turnover and restructuring of the actin cytoskeleton. It is found in all eukaryotic organisms in most cells. Profilin is important for spatially and temporally controlled growth of actin microfilaments, which is an essential process in cellular locomotion and cell shape changes. This restructuring of the actin cytoskeleton is essential for processes such as organ development, wound healing, and the hunting down of infectious intruders by cells of the immune system.
Profilin also binds sequences rich in the amino acid proline in diverse proteins. While most profilin in the cell is bound to actin, profilins have over 50 different binding partners. Many of those are related to actin regulation, but profilin also seems to be involved in activities in the nucleus such as mRNA splicing.
Profilin binds some variants of membrane phospholipids (Phosphatidylinositol (4,5)-bisphosphate and Inositol triphosphate). The function of this interaction is the sequestration of profilin in an "inactive" form, from where it can be released by action of the enzyme phospholipase C.
Profilin is the major allergen present in birch, grass, and other pollen.
Additional recommended knowledge
Profilin sources and distribution
Profilins are proteins of molecular weights of roughly 14 - 16 kDa. They are present as single genes in yeast, insects, and worms, and as multiple genes in many other organisms including plants. In mammalian cells, four profilin isoforms have been discovered; profilin-I is expressed in most tissues while profilin-II is predominant in brain and kidney.
Profilin in the regulation of actin dynamics
Profilin enhances actin growth in two ways:
Profilin is one of the most abundant actin monomer binders, but proteins such as CAP and (in mammals) thymosinβ4 have some functional overlaps with profilin. In contrast, ADF/cofilin has some properties that antagonize profilin action.
History of profilin discovery
Profilin was first described by Uno Lindberg and co-workers in the early 1970's as the first actin monomer binding protein. It followed the realization that not only muscle, but also non-muscle cells, contained high concentrations of actin, albeit in part in an unpolymerized form. Profilin was then believed to sequester actin monomers (keep them in a pro-filamentous form), and release them upon a signal to make them accessible for fast actin polymer growth.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Profilin". A list of authors is available in Wikipedia.|