Link to Pubmed [PMID] – 24552843
Link to DOI – 10.1016/j.ejcb.2014.01.003S0171-9335(14)00004-1
Eur J Cell Biol ; 93(5-6): 179-83
The primary function of Arp2/3 complex is the generation of free barbed ends by nucleating new filaments from the sides of pre-existing filaments. The pathway of branch formation is complex and involves nucleation promoting factors, actin monomers and nucleotides. A less prominent function of Arp2/3 complex is capping of actin filament pointed ends. Here we show, using electron microscopy, electron tomography, and image reconstruction of negatively-stained samples at ∼2-3nm resolution, that Arp2/3 complex bound to the pointed ends of actin filaments has a conformation similar to that in the branch junction with the Arps arranged in an actin-filament like configuration. This is direct evidence for the existence of two distinct activation pathways for Arp2/3 complex, one in the context of branch formation, one in the context of pointed-end capping, with essentially the same conformational end point.