Zinc binding directly regulates tau toxicity independent of tau hyperphosphorylation.
Bottom Line: Tau hyperphosphorylation is thought to underlie tauopathy.Elimination of zinc binding through amino acid substitution of Cys residues has a minimal effect on phosphorylation levels yet essentially eliminates Tau toxicity.These results indicate zinc binding is a substantial contributor to tauopathy and have implications for therapy development.
Affiliation: State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing 100084, China.Show MeSH
Related in: MedlinePlus
Mentions: One caveat associated with mutating Cys to Ala in Tau* is that, in addition to loss of zinc binding, the amino acid substitution might also affect other biological aspects of Tau. To address this question, we made additional Tau* mutants: Tau*C291H and Tau*C2H (C291H and C322H). We reasoned that, if loss of zinc binding is indeed the sole factor attributed to the decrease in toxicity, Tau*C291H (relative to Tau*C291A) or Tau*C2H (relative to Tau*C2A) may regain zinc-binding ability as histidine residues are also often utilized by proteins to bind zinc. If this were the case, we would expect these mutants to restore zinc-responsive toxicity in Tau. When assayed by fluorescence quenching, the two Tau* mutants exhibited better zinc response than the non-zinc binding Tau*C2A, though neither as well as Tau* itself. Tau*C2H, in particular, binds zinc significantly more weakly (Figure 6A). Both exhibited very little toxicity under normal conditions when assayed by longevity (Figures 6B and 6C). However, when the zinc levels were increased, Tau*C291H and to a lesser extent Tau*C2H regained toxicity (Figures 6B and 6C). In fact, in the survival assay, elevated zinc concentrations caused Tau*C291H to exhibit a level of toxicity nearly comparable to that of Tau* under nonelevated zinc concentrations. Brain sectioning revealed similar results (Figures 6D1 and 6D2). These results are in contrast with what was observed with C to A changes, which were relatively insulated from zinc alterations. The correlation between Tau* toxicity and zinc-binding ability, together with the Tau*C2A and dTau results, provide strong support for our model that the toxicity loss associated with mutating cysteine residues results from an attenuation or loss in zinc binding, but not other factors.
Affiliation: State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing 100084, China.