Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
Hui-Ting Chou
Department of Cell Biology, Harvard Medical School, Boston, United States
Chad A Brautigam
Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States; Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, United States
Wenmin Xing
Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
Sheng Yang
Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, United States
Lisa Henry
Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
Lynda K Doolittle
Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, United States; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, United States
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.
