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Paired helical filaments (PHFs) are a family of single filament structures with a common helical turn period: Negatively stained PHF imaged by TEM and measured before and after sonication, deglycosylation, and dephosphorylation
Author(s) -
Ruben George C.,
Wang Jianzhi,
Iqbal Khalid,
GrundkeIqbal Inge
Publication year - 2005
Publication title -
microscopy research and technique
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.536
H-Index - 118
eISSN - 1097-0029
pISSN - 1059-910X
DOI - 10.1002/jemt.20197
Subject(s) - chemistry , sonication , dephosphorylation , protein filament , biophysics , crystallography , analytical chemistry (journal) , chromatography , phosphorylation , biochemistry , biology , phosphatase
Isolated paired helical filaments (PHFs) were visualized on glutaraldehyde vapor‐treated thin ∼10‐nm thick indirect carbon films using high‐resolution transmission electron microscopy (TEM) and the negative stain, phosphotungstate acid (PTA) at near neutral pH of 6.8. PHF preparations were prepared with and without 1 minute of sonication. These same PHF were also deglycosylated with endoglycosidase F/N‐glycosidase F for 1 hour or the PHF were dephosphorylated with PP‐2A for 1 hour. The negatively stained PHF filaments were quantitatively studied by measuring their wide regions (W) their thin regions (T) and their helical turn period (L) and these separate parameters were averaged for each filament. In the unsonicated PHF preparation there were PHF, cylindrical filaments with periodic thin regions (CF‐PT), cylindrical filaments (CF), as well as 2.0‐nm tau polymer‐like filaments. The CF‐PT were characterized by W, T, and L measurements and the CF were characterized by diameter measurements. The paired helical filament model proposed by Kidd (1963, Nature 197:192–193) of two ∼10 nm filaments twisting around each other every ∼80 nm with a thin region of 10 nm and a wide region of 25 nm does not correspond to the PHF structures found. None of the PHF we observed were composed of a pair of filaments and all of the PHF appear to be a single filament. The wide regions ranged from 12.5–27 nm and the thin regions ranged from 4.5–12.3 nm. The helical turn periods ranged from 76–85 nm and were generally about 80 nm. Only the helical turn period of ∼80 nm was a common property of the whole family of PHF structures. The CF‐PT appear to be a PHF precursor filament. Deglycosylation of the PHF and CF‐PT reduced their sizes by 0.5–0.6 nm and 0.7–1.0 nm, respectively, and the right‐hand helicity of the PHF was lost after deglycosylation. Dephosphorylation with PP‐2A reduced the PHF wide regions by 6.0 nm and the thin regions by 2.6 nm. Microsc. Res. Tech. 67:175–195, 2005. © 2005 Wiley‐Liss, Inc.