Understanding the Kinetic Roles of 14-3-3ζ during Tau Filament Formation

Abstract

The microtubule associated protein tau and 14-3-3ζ protein are two proteins highly expressed in the central nervous system. Tau protein promotes microtubule assembly and aberrant accumulation of tau and formation of amyloid fibrils are pathological hallmarks of neurodegenerative tauopathies including Alzheimer's disease. Extensive studies have suggested that polyanionic inducers, such as heparin, interact with tau directly and induce specific conformational changes within tau, accelerating the amyloidogenesis process. 14-3-3ζ proteins form homodimers and bind their targets through specific pSer/pThr motifs. It has been found that tau protein contains two 14-3-3ζ-binding motifs, i.e., pSer214 and pSer324, and tau protein interacts with 14-3-3ζ protein directly. Furthermore, 14-3-3ζ is able to induce tau aggregation, although it's still controversial whether this process depends on tau phosphorylation. Here, we investigated the kinetic roles of 14-3-3ζ during tau filament formation. We used the K18 constructs of tau that consists of the four microtubule repeats and the pSer324 14-3-3ζ-binding motifs. Our results showed that 14-3-3ζ induced tau K18 aggregation at a rate much larger than that from full-length tau. Kinetics analyses showed that the lag time and rate of aggregation were dependent on the stoichiometry of tau to 14-3-3ζ. Although phosphorylation at Ser324 increased the binding affinity of tau K18 to 14-3-3ζ, phosphorylation only showed marginal effect on 14-3-3ζ mediated tau aggregation. Our results suggest that the formation of the 2:1 complex of tau monomer and 14-3-3ζ dimer plays an important role in the 14-3-3ζ mediated tau aggregation process.