Marta Carroni-Abstract

Conformational changes of Neurofibromin highlight the mechanism of Ras regulation

Abstract

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Mutations on the protein Neurofibromin (Nf) cause the autosomal disease neurofibromatosis type 1 and are related to up to 10% of the randomly occurring cancers. Neurofibromin works by enhancing GTP hydrolysis by the oncogenic protein Ras, resulting in Ras downregulation. While structural information of the GTPase-activating protein-related domain (GRD) and the lipid-binding Sec14-PH domain of Nf was available from X-ray crystallography studies, the overall molecular assembly of Nf was not known. We have determined the cryo-EM structure of the human Nf isoform 2 dimer at an overall resolution of 3.3 Å. The cryo-EM structure shows the presence of a scaffold domain made of N-HEAT/ARM repeats that harbor the functional GRD and Sec14-PH regions. More interestingly, 3D classification reveals the presence of two functionally different Nf states. In one state, that we call closed, Nf is in a self-inhibited and Zn-stabilized conformation with the HEAT/ARM core domains shielding the GRD so that Ras binding is sterically inhibited. In a second state, that we call open, one Nf protomer undergoes a large-scale movement of the GRD, which is necessary for Ras binding. The transition between the closed, self-inhibited and the open Nf states provides guidance for targeted studies for deciphering the complex molecular mechanism behind neurofibromatosis and Nf dysfunction in carcinogenesis.