The Structural Basis of Rho Effector Recognition Revealed by the Crystal Structure of Human RhoA Complexed with the Effector Domain of PKN/PRK1

The small G protein Rho has emerged as a key regulator of cellular events involving cytoskeletal reorganization. Here we report the 2.2 Å crystal structure of RhoA bound to an effector domain of protein kinase PKN/PRK1. The structure reveals the antiparallel coiled-coil finger (ACC finger) fold of the effector domain that binds to the Rho specificity-determining regions containing switch I, β strands B2 and B3, and the C-terminal α helix A5, predominantly by specific hydrogen bonds. The ACC finger fold is distinct from those for other small G proteins and provides evidence for the diverse ways of effector recognition. Sequence analysis based on the structure suggests that the ACC finger fold is widespread in Rho effector proteins.