Clinically observed RASA1 missense mutants exhibit diverse RasGAP protein behaviors

The RASA1 gene is mutated in cerebrovascular disorders and cancer, yet how the resulting mutations in the GTPase Activating Protein, RasGAP (p120RasGAP, RASA1) dysregulate signaling remains poorly understood. Here, we catalogue currently reported disease-associated mutations in RASA1 and assess their impact on RasGAP protein in vitro. On mapping these mutations onto experimental structures and structural models of RasGAP we identify regions that suggest functional impact. We assess key mutations within these regions for their effects on protein expression, thermal stability, and their interactions with a known binding partner, p190RasGAP. We then assess Michaelis-Menten kinetics of the mutant RasGAP proteins towards Ras. Together, we find that disease-associated RasGAP mutations classify into a panel of distinct classes based on their mode of dysregulation. We demonstrate that protein stability is necessary but not sufficient for full catalytic activity and that destabilizing mutations across the length of the protein can disrupt this function, but that the C2 domain appears to be unique in its role of regulating GAP activity by mechanisms other than destabilization involving the interactions of specific residues.