Interaction of the Proline-Rich Domain of Fission Yeast WASp (Ws1p1) with Actin Filaments

BackgroundThe Wiskott-Aldrich Syndrome protein (WASp) family of proteins plays a crucial role in the activation of the Arp2/3 (actin-related protein 2/3) complex to promote the branching of actin filaments. The proline-rich domain (PRD) of WASp is known to contribute to branching nucleation but was overlooked, until experiments showed that the PRD of budding yeast Las17 can bind actin filaments (1). MethodsWe purified recombinant proline-rich domains from fission yeast S. pombe Wsp1 and budding yeast S. cerevisiae Las17 to test in biochemical assays of actin binding and polymerization. ResultsThe PRD of the S. pombe Wsp1 binds actin filaments with micromolar affinity. The PRDs of both Wsp1 and Las17 slowed the rate of actin filament elongation by Mg-ATP-actin monomers by half and slowed the spontaneous polymerization of Mg-ATP-actin monomers modestly. ConclusionThe affinity of PRDs of WASp-family proteins for actin filaments is high enough to contribute to the reported stimulation of actin filament branching by Arp2/3 complex.