Structure of the TSC2 GAP Domain: Mechanistic Insight into Catalysis and Pathogenic Mutations

The TSC complex is the cognate GTPase-activating protein (GAP) for the small GTPase Rheb and a crucial regulator of the mechanistic target of rapamycin complex 1 (mTORC1). Mutations in the TSC1 and TSC2 subunits of the complex cause tuberous sclerosis complex (TSC). We present the crystal structure of the catalytic asparagine-thumb GAP domain of TSC2. A model of the TSC2-Rheb complex and molecular dynamics simulations suggest that TSC2 Asn1643 and Rheb Tyr35 are key active site residues, while Rheb Arg15 and Asp65, previously proposed as catalytic residues, contribute to the TSC2-Rheb interface and indirectly aid catalysis. The TSC2 GAP domain is further stabilized by interactions with other TSC2 domains. We characterize TSC2 variants that partially affect TSC2 functionality and are associated with atypical symptoms in patients, suggesting that mutations in TSC1 and TSC2 might predispose to neurological and vascular disorders without fulfilling the clinical criteria for TSC. [Display omitted] •Crystal structure of TSC2 GAP domain and model of human Rheb-TSC2 GAP complex•Key residues for activity are required for catalysis and specificity•Partial loss of function of TSC2 patient variants without definite diagnosis of TSC•TSC2 GAP domain interacts with additional domains in TSC2 Hansmann et al. report the crystal structure of the catalytic GAP domain of the tumor suppressor TSC2, providing novel insight into the enzyme mechanism and pathogenic mutations that cause the genetic disease tuberous sclerosis complex.