 Through its NF1-GRD domain, neurofibromin increases the rate of GTP hydrolysis of Ras, and acts as a tumor suppressor by reducing Ras activity.When the Ras-Nf1 complex assembles, active Ras binds in a groove that is present in the neurofibromin catalytic domain.This binding occurs through Ras switch regions I and II, and an arginine finger present in neurofibromin.