Arp 2/3 complex

The seven subunits of the Arp 2/3 complex

The Arp 2/3 complex is a protein complex that plays an important role in the formation of actin filaments from G-actin (actin nucleation ). It consists of seven sub-units.

Structure and function

The seven subunits of the complex are Arp2 , Arp3 , p16 , p20 , p21 , p34 and p40 , and ARPC1A , respectively . Together they form a protein weighing around 220 kilodaltons that allows cells to rapidly polymerize from G- to F-actin. It is assumed that the subunits Arp2 and Arp3 because of their homologuesStructure to actin mimicking an actin dimer, which is more stable than a real actin dimer and forms the basis for further polymerization. So-called "Nucleation Promoting Factor (NPFs)" proteins, such as proteins of the WASP / WAVE family , are required for activation for the complex to be active. The NPFs bind with a C-terminal CA region to the other four subunits (not Arp2 / Arp3 ) and at the same time to actin via a verproline- like region. This presumably leads to a change in the conformation of the Arp 2/3 complex, which leads to the formation of a nucleation center together with the actin involved. The entire complex then resembles one end of an actin filament. ${\ displaystyle +}$

In addition, the Arp 2/3 complex can cross-link actin filaments in a Y-shape at an angle of 70 °. There are two hypotheses about the exact process involved in this networking:

Dendritic nucleation

Model of dendritic nucleation: The Arp 2/3 complex binds to the side of F-actin after activation by NPFs and interaction with existing actin filaments. Starting from this "mother filament", a "daughter filament" is now nucleated, which protrudes from the mother filament at an angle of 70 °.

"barbed end branching"

Model of "barbed end branching" (branching of the ends: the complex binds to one end of an actin filament and induces a Y-branching into two "daughter filaments" of equal length). ${\ displaystyle +}$ ${\ displaystyle +}$

Individual evidence

↑ ^a ^b ^c Julia Ehinger: Characterization of Arp 2/3 complex mediated actin reorganization in the invasion of bacterial pathogens , Carolo-Wilhelmina University of Braunschweig, February 20, 2006, p. 9f. (Dissertation to obtain the degree of doctorate in natural sciences)

[Ehinger-1] Julia Ehinger: Characterization of Arp 2/3 complex mediated actin reorganization in the invasion of bacterial pathogens , Carolo-Wilhelmina University of Braunschweig, February 20, 2006, p. 9f. (Dissertation to obtain the degree of doctorate in natural sciences)