Polypeptide composition of paired helical filaments

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Immunocytochemical studies on paired helical filaments (PHF) yielded conflicting data due to antibody cross-reactivity.
• A protein chemical approach was developed to unambiguously identify PHF components.

Purpose of the Study:

• To identify the definitive protein components of paired helical filaments (PHF).
• To resolve ambiguities in PHF composition arising from immunological cross-reactivities.

Main Methods:

• Paired helical filaments (PHF) were treated with formic acid and digested with lysylendopeptidase.
• Resultant peptides were separated using High-Performance Liquid Chromatography (HPLC).
• Amino acid composition and sequences of major peptide peaks were analyzed.

Main Results:

• Proteolytic fragments of ubiquitin, tau, and beta-protein were sequenced from the PHF digest.
• Ubiquitin was identified in a conjugated form within PHF, with its target protein unidentified.
• Tau protein was found integrated into PHF at its carboxyl third.
• Beta-protein fragments were attributed to contamination from amyloid filaments.

Conclusions:

• Ubiquitin and tau are confirmed as the two definite components of paired helical filaments (PHF).
• This protein chemical approach provides a reliable method for identifying PHF constituents.