Alzheimer paired helical filaments (PHFs) studied by high-resolution TEM: what can vertical Pt-C replication tell us about the organization of the pronase-digested PHF core?
Untreated paired helical filaments (PHFs) and pronase-digested PHF-core filaments were stereoscopically imaged with a freeze-drying vertical platinum-carbon replication preparation method for TEM. The untreated PHF have an average wide region (W) = 22.8 +/- 2.4 nm, a narrow region (T) = 10.6 +/- 1.7 nm, and a helical turn period (L) = 78.6 +/- 13.4. The surfaces of the untreated PHF's fuzzy coat appears disorganized. The widths of the pronase-treated PHF-core filaments were significantly reduced (W(d) = 14.8 +/- 1.2 nm, T(d) = 5.7 +/- 1.0 nm, and L(d) = 75.4 +/- 17 nm). The surfaces of the untreated PHF contained approximately 1.1 nm strands, the same size as tau monomer ( approximately 1.0 nm). The pronase-digested PHF cores mostly contained approximately 1.6 +/- 0.3 nm strands although strand diameters ranged from 0.6-2.5 nm. The strands sometimes appear to be wrapped around the filament axis; less often, they appear to be roughly parallel to the PHF axis, and otherwise appear to be randomly oriented. Images of pronase-digested PHF core images are discussed in relation to the core's biochemical composition, its proposed beta structure, and structural subunit models. Images of the untreated and the pronase-digested PHF support a helical ribbon morphology.
Ruben
George C
GC
Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA. George.C.Ruben@Dartmouth.Edu
Novak
Michal
M
Edwards
Patricia C
PC
Iqbal
Khalid
K
D000544:Alzheimer Disease / Q000473:pathology*; D005612:Freeze Drying; D006801:Humans; D008297:Male; D046529:Microscopy, Electron, Transmission; D008875:Middle Aged; D016874:Neurofibrillary Tangles / Q000737:chemistry / Q000648:ultrastructure*; D011402:Pronase / Q000737:chemistry; D016628:Replica Techniques
D011402:Pronase