Comparative study of the prereactive protein kinase A Michaelis complex with kemptide substrate.

In the present work we have modeled the Michaelis complex of the cyclic-Adenosine Monophosphate Dependent (cAMD) Protein Kinase A (PKA) with Mg(2)ATP and the heptapeptide substrate Kemptide by classical molecular dynamics. The chosen synthetic substrate is relevant for its high efficiency and small size, and it has not been used in previous theoretical studies. The structural analysis of the data generated along the 6 ns simulation indicates that the modeled substrate-enzyme complex mimics the substrate binding pattern known for PKA. The values of the average prereactive distances obtained from the simulation do not exclude any of the two limiting situations proposed as mechanisms in the literature for the phosphorylation reaction (dissociative and associative) because the system oscillates between configurations compatible with each of them. Furthermore, the results obtained for the average interaction distances between active site residues concord in suggesting the plausibility of an alternative third reaction mechanism.