Rac1 GTPase activates the WAVE regulatory complex through two distinct binding sites

Elife. 2017 Sep 26;6:e29795. doi: 10.7554/eLife.29795.

Abstract

The Rho GTPase Rac1 activates the WAVE regulatory complex (WRC) to drive Arp2/3 complex-mediated actin polymerization, which underpins diverse cellular processes. Here we report the structure of a WRC-Rac1 complex determined by cryo-electron microscopy. Surprisingly, Rac1 is not located at the binding site on the Sra1 subunit of the WRC previously identified by mutagenesis and biochemical data. Rather, it binds to a distinct, conserved site on the opposite end of Sra1. Biophysical and biochemical data on WRC mutants confirm that Rac1 binds to both sites, with the newly identified site having higher affinity and both sites required for WRC activation. Our data reveal that the WRC is activated by simultaneous engagement of two Rac1 molecules, suggesting a mechanism by which cells may sense the density of active Rac1 at membranes to precisely control actin assembly.

Keywords: Arp2/3 complex; Rho family GTPase; WASP family protein; actin assembly; biophysics; human; signal integration; signal transduction; structural biology.

MeSH terms

  • Actins / metabolism
  • Adaptor Proteins, Signal Transducing / metabolism
  • Binding Sites
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Carrier Proteins / ultrastructure*
  • Cryoelectron Microscopy
  • Cytoskeletal Proteins / metabolism
  • DNA Mutational Analysis
  • Humans
  • Protein Binding
  • Protein Multimerization*
  • Proteins / metabolism
  • Wiskott-Aldrich Syndrome Protein Family / metabolism
  • rac1 GTP-Binding Protein / metabolism*
  • rac1 GTP-Binding Protein / ultrastructure*
  • tRNA Methyltransferases

Substances

  • ABI2 protein, human
  • Actins
  • Adaptor Proteins, Signal Transducing
  • BRK1 protein, human
  • Carrier Proteins
  • Cytoskeletal Proteins
  • Proteins
  • WASF1 protein, human
  • Wiskott-Aldrich Syndrome Protein Family
  • steroid receptor RNA activator, human
  • TRMO protein, human
  • tRNA Methyltransferases
  • rac1 GTP-Binding Protein