Global hairpin folding of tau in solution.
The microtubule-associated protein tau stabilizes microtubules in its physiological role, whereas it forms insoluble aggregates (paired helical filaments) in Alzheimer's disease. Soluble tau is considered a natively unfolded protein whose residual folding and intramolecular interactions are largely undetermined. In this study, we have applied fluorescence resonance energy transfer (FRET) and electron paramagnetic resonance (EPR) to examine the proximity and flexibility of tau domains and the global folding. FRET pairs spanning the tau molecule were created by inserting tryptophans (donor) and cysteines (labeled with IAEDANS as an acceptor) by site-directed mutagenesis. The observed FRET distances were significantly different from those expected for a random coil. Notably, the C-terminal end of tau folds over into the vicinity of the microtubule-binding repeat domain, the N-terminus remains outside the FRET distance of the repeat domain, yet both ends of the molecule approach one another. The interactions between the domains were obliterated by denaturation in GdnHCl. Paramagnetic spin-labels attached in various domains of tau were analyzed by EPR and exhibited a high mobility throughout. The data indicate that tau retains some global folding even in its "natively unfolded" state, combined with the high flexibility of the chain.
Max Planck Unit for Structural Molecular Biology, Notkestrasse 85, D-22607 Hamburg, Germany.
Sadasivam
S
Jeganathan
Martin
M
von Bergen
Henrik
H
Brutlach
Heinz-Jürgen
HJ
Steinhoff
Eckhard
E
Mandelkow
D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D031541:Fluorescence Resonance Energy Transfer; D016297:Mutagenesis, Site-Directed; D009282:Naphthalenesulfonates / Q000737:chemistry; D017510:Protein Folding; D012996:Solutions; D016875:tau Proteins / Q000737:chemistry* / Q000235:genetics
D009282:Naphthalenesulfonates; D012996:Solutions; D016875:tau Proteins; C006421:1,5-I-AEDANS