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Arp2/3 complex is bound and activated by two WASP proteins.

Shae B Padrick¹, Lynda K Doolittle, Chad A Brautigam

¹Howard Hughes Medical Institute and Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.

Proceedings of the National Academy of Sciences of the United States of America

|June 17, 2011

Summary

The Arp2/3 complex initiates actin filament formation, guided by WASP proteins. This study reveals that two VCA domains, not one, activate the Arp2/3 complex at distinct sites, refining our understanding of this crucial cellular process.

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Area of Science:

Cell Biology
Biochemistry
Molecular Biology

Background:

The Arp2/3 complex is essential for nucleating actin filaments in eukaryotic cells.
Activation is signaled by Wiskott-Aldrich syndrome protein (WASP) family proteins, specifically their VCA domain.
Previous models proposed a single VCA interaction for Arp2/3 complex activation.

Purpose of the Study:

To investigate the mechanism of Arp2/3 complex activation by WASP VCA domains.
To elucidate the specific binding sites and roles of VCA domains in activation.
To resolve conflicting literature regarding VCA-mediated Arp2/3 complex activation.

Main Methods:

Experimental investigation of VCA domain interactions with the Arp2/3 complex.
Analysis of conformational changes induced by VCA binding.
Characterization of actin monomer delivery by VCA domains.

Main Results:

Arp2/3 complex activation involves two VCA molecules engaging two distinct sites.
One VCA site is on Arp3, while the second involves ARPC1 and Arp2.
VCAs at these distinct sites play different roles in the activation process.

Conclusions:

A new model for Arp2/3 complex activation by WASP VCA domains is proposed.
This model involves dual VCA engagement and distinct functional roles at each site.
The findings reconcile previous disparate observations on VCA-Arp2/3 complex interactions.