PAIRED HELICAL FILAMENTS ARE TWISTED RIBBONS COMPOSED OF 2 PARALLEL AND ALIGNED COMPONENTS - IMAGE-RECONSTRUCTION AND MODELING OF FILAMENT STRUCTURE USING ATOMIC-FORCE MICROSCOPY

To study the structure of Alzheimer paired helical filaments (PHF) we examined isolated detergent-insoluble PHF using atomic force microscop y with image reconstruction. The reconstructed AFM images of Alzheimer PHF most closely resembled ribbon-like helices with thin edges. The p resence of a conspicuous furrow in the PHF midline indicated that PHF were composed of two distinctive strands. Our present conception of th e overall configuration of PHF is consistent with that proposed by Cro wther and Wischik in 1985 but includes an essential component of the p revailing model: the presence of two strands. Thus, our new model of P HF structure, based on atomic force microscopy-derived data, indicates that the true structure of PHF is actually a hybrid of the prevailing PHF model and a thin helical ribbon.