The Tau protein exhibits protein kinase activity throughout nearly the entire sequence, but it lacks traditional serine/threonine or tyrosine kinase activity, as demonstrated in Table . Rather, it primarily exhibits three kinase activities: HPr(Ser) kinase, pyruvate kinase, and RIO kinase. The tau protein activates its kinase activity by binding to Mg2+-ATP. Tau protein contains two Mg2+-ATP binding sites: one at aspartate (D13) and the other at glycine (G682). Near the downstream of G682, there are two lysines (K). Consequently, the catalytic domain concludes at G682, while the central portion of the domain is D13. After the G682 region binds to it, D13 bonds to Mg2+-ATP, granting Tau protein kinase activity. The D13 region reflects the RIO kinase activity of the Tau protein and also possesses catalytic activity. The D13 region is the only part of the Tau protein's HPr(Ser) kinase domain that is in charge of phosphorylating serine and threonine residues.