Interaction of WASP/Scar proteins with actin and vertebrate Arp2/3 complex

Abstract

The Wiskott–Aldrich-syndrome protein (WASP) regulates polymerization of actin by the Arp2/3 complex. Here we show, using fluorescence anisotropy assays, that the carboxy-terminal WA domain of WASP binds to a single actin monomer with a Kd of 0.6 μM in an equilibrium with rapid exchange rates. Both WH-2 and CA sequences contribute to actin binding. A favourable ΔH of −10 kcal mol−1 drives binding. The WA domain binds to the Arp2/3 complex with a Kd of 0.9 μM; both the C and A sequences contribute to binding to the Arp2/3 complex. Wiskott–Aldrich-syndrome mutations in the WA domain that alter nucleation by the Arp2/3 complex over a tenfold range without affecting affinity for actin or the Arp2/3 complex indicate that there may be an activation step in the nucleation pathway. Actin filaments stimulate nucleation by producing a fivefold increase in the affinity of WASP-WA for the Arp2/3 complex.

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Marchand, JB., Kaiser, D., Pollard, T. et al. Interaction of WASP/Scar proteins with actin and vertebrate Arp2/3 complex. Nat Cell Biol 3, 76–82 (2001). https://doi.org/10.1038/35050590

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