[Amyloidosis, protein conformation dynamics and neurologic diseases].

The abnormal protein which accumulates in the extracellular space in the central nervous system in Alzheimer's disease and prion diseases could result from similar mechanisms. Many studies have demonstrated that the abnormal protein is resistant to proteolytic agents. This resistance is correlated with a modification in the conformation of the protein, inverting the ratio of alpha and beta helix structures. This change in conformation could be the cause of the central nervous system lesions. The mechanism of the modification in conformation could be related to a process of hydrophobisation of the protein resulting from mutation. A hydrophilic amino acid would be replaced by a hydrophobic amino acid or in sporadic forms, modifications in the environment of the peptide may lead to physical and chemical aggressions. Hydrophobisation of the two proteins could later lead to formation of polymers and then insoluble aggregates with the physical and chemical characteristics of the amyloid substance. Polymerisation could be triggered by the formation of protein dimers which would be, in one case, an endogenous protein, PrP, and in the other exogenous proteins coming from the environment.