Hyperphosphorylation induces structural modification of tau-protein.

The effect of hyperphosphorylation on the structural properties and conformational stability of bovine tau-protein was studied by means of circular dichroism and fluorescence lifetime techniques. Normal protein contains unusual secondary structure elements: extended left-handed helices. The structure of this protein was assumed to be of a 'tadpole' type - a globular C-terminal part with a long and rigid tail included in the extended left-handed helix. Either a decrease or an increase of pH induced only minor changes of the normal tau-protein surface. Hyperphosphorylation affected the extended part of the protein molecule; the decrease of pH in this case induced considerable structural rearrangements, and the conformation of the C-terminal part of the protein molecule was transformed into a molten globule-like state.