Nucleation-dependent tau filament formation: the importance of dimerization and an estimation of elementary rate constants.
Filamentous inclusions composed of the microtubule-associated protein tau are found in Alzheimer disease and other tauopathic neurodegenerative diseases, but the mechanisms underlying their formation from full-length protein monomer under physiological conditions are unclear. To address this issue, the fibrillization of recombinant full-length four-repeat human tau was examined in vitro as a function of time and submicromolar tau concentrations using electron microscopy assay methods and a small-molecule inducer of aggregation, thiazine red. Data were then fit to a simple homogeneous nucleation model with rate constant constraints established from filament dissociation rate, critical concentration, and mass-per-unit length measurements. The model was then tested by comparing the predicted time-dependent evolution of length distributions to experimental data. Results indicated that once assembly-competent conformations were attained, the rate-limiting step in the fibrillization pathway was tau dimer formation. Filament elongation then proceeded by addition of tau monomers to nascent filament ends. Filaments isolated at reaction plateau contained approximately 2 tau protomers/beta-strand spacing on the basis of mass-per-unit length measurements. The model suggests four key steps in the aggregation pathway that must be surmounted for tau filaments to form in disease.
Congdon
Erin E
EE
Center for Molecular Neurobiology, Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA.
Kim
Sohee
S
Bonchak
Jonathan
J
Songrug
Tanakorn
T
Matzavinos
Anastasios
A
Kuret
Jeff
J
D001703:Biophysics / Q000379:methods; D019281:Dimerization; D006801:Humans; D007700:Kinetics; D008870:Microtubules / Q000737:chemistry; D008954:Models, Biological; D008956:Models, Chemical; D015233:Models, Statistical; D016011:Normal Distribution; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D013696:Temperature; D013843:Thiazines / Q000494:pharmacology; D013997:Time Factors; D016875:tau Proteins / Q000737:chemistry*
D011994:Recombinant Proteins; D013843:Thiazines; D016875:tau Proteins