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J Biol Chem. 2008 Jun 13;283(24):16950-9. doi: 10.1074/jbc.M800783200. Epub 2008 Mar 31.

Functional surfaces on the p35/ARPC2 subunit of Arp2/3 complex required for cell growth, actin nucleation, and endocytosis.

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  • 1Department of Biochemistry, Brandeis University and the Rosenstiel Basic Medical Sciences Center, Waltham, Massachusetts 02454, USA.

Abstract

The Arp2/3 complex is comprised of seven evolutionarily conserved subunits and upon activation by WASp or another nucleation promoting factor nucleates the formation of actin filaments. These events are critical for driving a wide range of cellular processes, including motility, endocytosis, and intracellular trafficking. However, an in depth understanding of the Arp2/3 complex activation and nucleation mechanism is still lacking. Here, we used a mutagenesis approach in Saccharomyces cerevisiae to dissect the structural and functional roles of the p35/ARPC2 subunit. Using integrated alleles that target conserved and solvent-exposed residues, we identified surfaces on p35/ARPC2 required for cell growth, actin organization, and endocytosis. In parallel, we purified the mutant Arp2/3 complexes and compared their actin assembly activities both in the presence and in the absence of WASp. The majority of alleles with defects mapped to one face of p35/ARPC2, where there was a close correlation between loss of actin nucleation and endocytosis. A second site required for nucleation and endocytosis was identified near the contact surface between p35/ARPC2 and p19/ARPC4. A third site was identified at a more distal conserved surface, which was critical for endocytosis but not nucleation. These findings pinpoint the key surfaces on p35/ARPC2 required for Arp2/3 complex-mediated actin assembly and cellular function and provide a higher resolution view of Arp2/3 structure and mechanism.

PMID:
18381280
[PubMed - indexed for MEDLINE]
PMCID:
PMC2423265
Free PMC Article

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