Journal Article

Selective Disactivation of Neurofibromin GAP Activity in Neurofibromatosis Type 1 (NF1)

Anja Klose, M. Reza Ahmadian, Markus Schuelke, Klaus Scheffzek, Sven Hoffmeyer, Andreas Gewies, Frank Schmitz, Dieter Kaufmann, Hartmut Peters, Alfred Wittinghofer and Peter Nürnberg

in Human Molecular Genetics

Volume 7, issue 8, pages 1261-1268
Published in print August 1998 | ISSN: 0964-6906
Published online August 1998 | e-ISSN: 1460-2083 | DOI:
Selective Disactivation of Neurofibromin GAP Activity in Neurofibromatosis Type 1 (NF1)

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Neurofibromatosis type 1 (NF1) is a common familial tumour syndrome with multiple clinical features such as neurofibromas, café-au-lait spots (CLS), iris Lisch nodules, axillary freckling, optic glioma, specific bone lesions and an increased risk of malignant tumours. It is caused by a wide spectrum of mutations affecting the NF1 gene. Most mutations result in the loss of one allele at the DNA, mRNA or protein level and thus in the loss of any function of the gene product neurofibromin. The idea of the simultaneous loss of several different neurofibromin functions has been postulated to explain the pleiotropic effects of its loss. However, we have identified a novel missense mutation in a family with a classical multi-symptomatic NF1 phenotype, including a malignant schwannoma, that specifically abolishes the Ras·GTPase-activating function of neu-rofibromin. In this family, Arg1276 had mutated into proline. Based on complex biochemical studies as well as the analysis of the crystal structure of the GTPase-activating protein (GAP) domain of p120GAP in the presence of Ras, we unequivocally identified this amino acid as the arginine finger of the neurofibromin GAP-related domain (GRD)—the most essential catalytic element for RasGAP activity. Here, we present data demonstrating that the mutation R1276P, unlike previously reported missense mutations of the GRD region, does not impair the secondary and tertiary protein structure. It neither reduces the level of cellular neurofibromin nor influences its binding to Ras substantially, but it does completely disable GAP activity. Our findings provide direct evidence that failure of neurofibromin GAP activity is the critical element of NF1 pathogenesis. Thus, therapeutic approaches aimed at the reduction of RasGTP levels in neural crest-derived cells can be expected to relieve most of the NF1 symptoms.

Journal Article.  5261 words.  Illustrated.

Subjects: Genetics and Genomics

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