τ Self‐Association: Stabilization with a Chemical Cross‐Linker and Modulation by Phosphorylation and Oxidation State

τ is a major component of paired helical filaments found in the neurofibrillary tangles of Alzheimer's diseased brain. However, the mechanism or mechanisms responsible for the association of τ to form these aggregates remains unknown. In this study, the role of intermolecular disulfide bonds in the formation of higher order oligomers of bovine τ and the human recombinant τ isoform T3 was examined using the chemical cross‐linking agent disuccinimidylsuberate (DSS). In addition, the role of phosphorylation and oxidation state on the in vitro self‐association of τ was studied using this experimental model. Stabilization of τ‐τ interactions with DSS indicated that intermolecular disulfide bonds probably play a predominant role in dimer formation, but the formation of higher order oligomers of τ cannot be attributed to these bonds alone. τ‐τ interactions were significantly decreased either by blocking Cys residues or by exposing the τ to a reducing (nitrogen and dithiothreitol), instead of an oxidizing, environment. τ self‐association was also significantly decreased by prior phosphorylation with calcium/calmodulin‐dependent protein kinase II. Phosphorylation by cyclic AMP‐dependent protein kinase or dephosphorylation by alkaline phosphatase did not alter τ self‐assembly. These data suggest a role for several factors that may modulate τ self‐association in vivo.