Is PrP(106-126) fragment involved in the membrane activity of the Prion protein?

Prion diseases are a class of fatal neurodegenerative disorders that affect mammals and are characterized by their unique transmissibility and the nature of the infectious agent. When the physiological prion protein (PrP(C)) become corrupted (PrP(Sc)) it accumulates in the brain, promoting infection and self-propagation via recruitment of PrP(C). Although with identical sequence, PrP(C) and PrP(Sc) differ in their physicochemical properties: PrP(C) is soluble, has an alpha-helical structure and is sensitive to enzymatic degradation, whereas PrP(Sc) is insoluble, forms beta-aggregates and is resistant to proteolysis. The fragment PrP(16-126) possess similar physicochemical and pathological properties to PrP(sc), and therefore is commonly used as a model to study pathogenic effects. Although the pathogenicity of prion diseases is still unclear, strong evidences suggest that the cell membrane is relevant not only in infection and propagation of the disease but also in the manifestation of the clinical symptoms. In particular, the fragment PrP(106-126) has been implicated in the perturbation of the membranes and in the manifestation of Prion diseases. However, this is controversial. This review will discuss the effect of PrP(106-126) on the cell membrane based on its effect on model phospholipid bilayers. Different conditions were studied, including membrane charge, viscosity, lipid composition, pH, and ionic strength, revealing that PrP(106-126) only interacts with lipid membranes at conditions with no physiological relevance. Such findings are here reviewed and correlated with the full-length protein effect.