Small molecules CK-666 and CK-869 inhibit actin-related protein 2/3 complex by blocking an activating conformational change.

Byron Hetrick, Min Suk Han, Luke A Helgeson, Brad J Nolen

Index: Chem. Biol. 20(5) , 701-12, (2013)

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Abstract

Actin-related protein 2/3 (Arp2/3) complex is a seven-subunit assembly that nucleates branched actin filaments. Small molecule inhibitors CK-666 and CK-869 bind to Arp2/3 complex and inhibit nucleation, but their modes of action are unknown. Here, we use biochemical and structural methods to determine the mechanism of each inhibitor. Our data indicate that CK-666 stabilizes the inactive state of the complex, blocking movement of the Arp2 and Arp3 subunits into the activated filament-like (short pitch) conformation, while CK-869 binds to a serendipitous pocket on Arp3 and allosterically destabilizes the short pitch Arp3-Arp2 interface. These results provide key insights into the relationship between conformation and activity in Arp2/3 complex and will be critical for interpreting the influence of the inhibitors on actin filament networks in vivo.Copyright © 2013 Elsevier Ltd. All rights reserved.