Structural basis for membrane-dependent positive feedback regulation of DOCK11 by activated Cdc42.

The guanine nucleotide exchange factor DOCK11 is widely expressed across tissues and activates Cdc42, a Rho family GTPase that regulates cytoskeletal remodeling and cell polarity. Loss-of-function mutations in DOCK11 have recently been linked to inborn errors of immunity. DOCK11 has also been implicated in facilitating hepatitis B virus infection in hepatocytes and has emerged as a potential target for therapeutic interventions. A positive feedback mechanism has been proposed for DOCK11-mediated Cdc42 activation; however, the structural basis for this regulation has remained unclear. Here we report the cryoelectron microscopy structures of full-length DOCK11 as an apo dimer, a binary complex with nucleotide-free Cdc42, and a ternary complex containing both nucleotide-free and activated Cdc42. DOCK11 predominantly adopts a U-shaped dimer that binds to nucleotide-free Cdc42 via the catalytic domain, whereas activated Cdc42 engages a distal site within the armadillo-repeat domain. Biochemical and cellular analyses demonstrate that binding of activated Cdc42 is critical for enhancing the membrane-dependent nucleotide exchange activity of DOCK11, promoting its localization to the plasma membrane, and facilitating intracellular activation of Cdc42. We also determined the structure of the membrane-bound ternary complex using membrane-coated grids. Strikingly, the ternary complex adopts an extended conformation that aligns multiple membrane-contact elements, revealing how activated Cdc42 stabilizes DOCK11 membrane binding for efficient exchange activity. Collectively, these findings provide a structural framework for the coordinated mechanism underlying membrane-dependent positive feedback in Rho GTPase signaling.