Introduction

Introduction

The Arp2/3 complex is responsible for nucleation of actin filaments to form branches at a distinct 70 degrees angle from the mother filament; ATP, an actin monomer, a mother filament and a nucleation promoting-factor needed to activate the complex which is intrinsically inactive. Several factors are known to interact with the Arp2/3 complex, most notably WASp. Structural features of the complex as a whole and particular subunits reveal clues about the mechanism of action of the Arp2/3-complex in the process of actin filament formation.

The structural images are based on a crystallized structure of the residues of the bovine Arp2/3 complex, at an 2.0 Angstrom resolution, as published by Robinson and colleagues [1], and retrieved from the Protein Database (PDB). 86% of the 1980 residues are included, with the major missing regions being subdomains 1 and 2 of the Arp2-subunit which showed a very weak electron density and steric clashing with Arp3 [2], indicating these subdomains are highly flexible. The complex is crystallized in its inactive form, with the Arp2 and Arp3 at a considerable distance from each other: earlier mentioned promoting factors are presumably involved in bringing Arp2 in closer proximity to Arp3, to allow nucleation to occur.

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