Tau Complex Inhibition by Prototype Inhibitors

Kinetic Studies of Cdk5/p25 Kinase:

Phosphorylation of Tau and Complex Inhibition by Two Prototype Inhibitors








These studies served as a necessary kinetic backdrop for investigations of the mechanism of inhibition by prototype inhibitors :

N4-(6-aminopyrimidin-4-yl)-sulfanilamide (APS) and 1-(5-cyclobutyl-thiazol-2-yl)-3-isoquinolin-5-yl-urea (CTIU).


We found that the cdk5/p25-catalyzed phosphorylation of tau follows a rapid equilibrium, random kinetic mechanism, as evidenced by initial velocity analysis indicating sequential addition of tau and ATP, and studies of the mechanism of inhibition by substrate analogue AMP, product ADP, and analogues of peptide substrate H1P. Identical mechanistic conclusions were drawn when H1P was the phosphoryl acceptor.



Subsequent studies of inhibition by APS and CTIU revealed that
both compounds can bind to all four steady-state forms of the enzyme,
to form the complexes E:I, E:I:tau, E:I:ATP, and E:I:tau:ATP.



These results contrast with reported claims that APS and CTIU are competitive inhibitors of the binding of ATP.