Profilin is an
actin-binding proteininvolved 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 actinmicrofilaments, 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 prolinein 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 mRNAsplicing.
Profilin binds some variants of membrane
phospholipids ( Phosphatidylinositol (4,5)-bisphosphateand 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
allergenpresent in birch, grass, and other pollen.
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 brainand kidney.Witke, W., Podtelejnikov, A., Di Nardo, A., Sutherland, J., Gurniak, C., Dotti, C., and M. Mann (1998) In Mouse Brain Profilin I and Profilin II Associate With Regulators of the Endocytic Pathway and Actin Assembly. The EMBO Journal17(4): 967-976 Entrez Pubmed|9463375]
Profilin in the regulation of actin dynamics
Profilin enhances actin growth in two ways:
* Profilin binds to monomeric actin thereby occupying an actin-actin contact site; in effect, profilin sequesters actin from the pool of polymerizable actin monomers. However, profilin also catalyzes the exchange of actin-bound ADP to ATP thereby converting poorly polymerizing ADP-actin monomers into readily polymerizing ATP-actin monomers. On top of that, profilin has a higher affinity for ATP- than for ADP-actin monomers. Thus in a mixture of actin, profilin, and nucleotides (ADP and ATP), actin will polymerize to a certain extent, which may be estimated by the
law of mass action.
* Profilin-actin complexes are fed into growing actin polymers by proteins such as
formin, WASP and VASP (that contain proline-rich FH2-domains). This mode of stimulated actin polymerization is much faster than unaided polymerization. Profilin is essential for this mode of polymerization because it recruits the actin monomers to the proline-rich proteins.
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/ cofilinhas 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.Carlsson L, Nyström LE, Sundkvist I, Markey F, Lindberg U. (1977) Actin polymerizability is influenced by profilin, a low molecular weight protein in non-muscle cells. J. Mol. Biol. 115:465-483 Entrez Pubmed|563468] 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.
PFN1, PFN2, PFN3, PFN4
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Look at other dictionaries:
Profilin 1 — Profilin 1, also known as PFN1, is a human gene. PBB Summary section title = summary text = The protein encoded by this gene is a ubiquitous actin monomer binding protein belonging to the profilin family. It is thought to regulate actin… … Wikipedia
Profilin — 1 Bändermodell von Profilin 1 (blau) gebunden an Aktin (grün), nach … Deutsch Wikipedia
profilin — profilin. См. профилин. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
profilin — Actin binding protein (15 kD) that forms a complex with G actin rendering it incompetent to nucleate F actin formation. The profilin actin complex seems to interact with inositol phospholipids that may regulate the availability of nucleation… … Dictionary of molecular biology
profilin — A small protein that binds to monomeric actin (thus becoming profilactin), preventing premature polymerization of actin. It also participates in the inhibition of one isoform of phospholipase C. * * * pro·fil·in (pro filґin) a 15 kD actin binding … Medical dictionary
profilin — … Useful english dictionary
PFN2 — Profilin 2, also known as PFN2, is a human gene.cite web | title = Entrez Gene: PFN2 profilin 2| url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene Cmd=ShowDetailView TermToSearch=5217| accessdate = ] PBB Summary section title = summary text … Wikipedia
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