Actin nucleation

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The actin nucleation exactly Aktinfilamentnukleation or just nucleation denotes the initial step in the formation of in biochemistry actin from actin monomers , that is, in the polymerization of actin.

Actin monomers (G-actin) combine to form polarized filaments (F-actin) that have a fast growing end and a slow growing end. The first step in this merger is called nucleation, which corresponds to the formation of stable multimers (so-called nucleation nuclei ) from three actin monomers.

However, the spontaneous nucleation of actin is thermodynamically unfavorable and proceeds only very slowly, which is due to the instability of actin-dimer intermediates and the activity of actin monomers. To overcome this energetic hurdle, cells use a variety of actin nucleation proteins, such as the Arp 2/3 complex , formin and tandem-monomer-binding nucleators , which are also called nucleation factors . As a result of these proteins, the reaction speed increases sharply. However, with each added monomer, the speed slows down a little.

Formin nucleation factor

The model around the nucleation factor formin, which is also known as the tip nucleation model (from the English "tip nucleation model"), states that proteins from the formin class group on the cell membrane and initiate nucleation. Formin then mediates the elongation of the filament, which is carried out through Fascin .

Nucleation factor Arp 2/3 complex

The Arp 2/3 complex is an alternative to formin, but is more likely to be associated with the lamellipodia , or general motile areas of a cell. It is assumed that the complex mimics an actin dimer, but at the same time is more stable than one and thus serves as a nucleation base. Connections from this complex may be further secured by Fascin.

Nucleating factor tandem-monomer-binding nucleator

This group of nucleation factors is so named because in each of these factors binding sites for actin monomers repeat in tandem. This group includes the spire proteins, cordon bleu (Cobl), leiomodin (Lmod-2), JMY and the adenomatous polyposis coli protein (ACP). And in each of these proteins there are in turn repetitions of binding sites for actin monomers, which can accumulate there.

Individual evidence

  1. ↑ a b GO: 0045010 actin nucleation . QuickGo, The European Bioinformatics Institute , accessed August 6, 2015.
  2. ^ A b Elif Nur Firat-Karalar and Matthew D. Welch: New mechanisms and functions of actin nucleation . In: Current Opinion in Cell Biology . 23, No. 1, February 2011, pp. 4-13. doi : 10.1016 / j.ceb.2010.10.007 . PMC 3073586 (free full text).
  3. ↑ a b Julia Ehinger: Characterization of the Arp 2/3 complex mediated actin reorganization during the invasion of bacterial pathogens , Carolo-Wilhelmina University of Braunschweig, February 20, 2006, pp. 2 and 9. (Dissertation to obtain the degree of doctorate in natural sciences)
  4. ↑ a b c Actin Nucleation . Mebinfo, October 20, 2014, accessed August 6, 2015.