Amyloid fibers deriving from the aromatic core of C-terminal domain of nucleophosmin 1

Nucleophosmin (NPM1) is the most frequently mutated gene in Acute Myeloid Leukemia (AML) patients and mutations lead to its aberrant cytoplasmatic accumulation in leukemic cells. Its C-terminal domain (CTD) is endowed with a globular structure consisting of a three-helix bundle in the wild type form that is disrupted by AML mutations. Our recent results demonstrate, unexpectedly and unequivocally, that regions of the CTD of NPM1 are prone to aggregate to amyloid states. Here we present novel studies, at solution as well as fibrillar states of a nonapeptide covering the 264–272 region of NPM1: this small fragment is the most amyloidogenic stretch of the entire protein and its conformational and aggregation properties were investigated through Circular Dichroism, Fluorescence spectroscopies, amyloid seeding assay (ASA), isothermal titration calorimetry (ITC) and electrospray ionization (ESI) mass analyses. Structural features of fibrils were investigated by means of Scanning Electron Microscopy (SEM) and Wide-Angle X-ray Scattering (WAXS). This study deepens the amyloid fibrillization process of a short stretch of the CTD likely involved in the propagative mechanism for NPMc+ cytoplasmatic accumulation in leukemogenesis.