(489g) Protein Oscillator Based On Multisite Phosphorylation/Dephosphorylation

Lots of analytical and computational work have been conducted to investigate the design principles underlying molecular and cellular oscillations, but phosphorylation/dephosphorylation (P/D) of a single protein has never been modeled as a potential source of oscillation. In this paper, we investigate the conditions under which a single-level protein P/D could create oscillation.

We consider a hypothetic protein substrate with n phosphorylation sites and assume Mechaelis-Menten kinetics for all phosphorylation and dephosphorylation reaction steps. To create a negative feedback, to return the system to its initial state, we assume that the fully phosphorylated state inhibits the phosphorylation of the unphosphorylated substrate.

Our computational results demonstrate that if the phosphorylated substrate inhibits substrate-kinase association in a cooperative manner, substrates that contain more than one site can show oscillatory behavior. There is an inverse correlation between the number of phosphorylation sites and the minimum cooperativity in the negative feedback required for driving the system into the oscillatory regime. The period and amplitude of oscillation are mainly determined by the initial concentration of the substrate and the number of phosphorylation sites. When the ratio of substrate/enzyme is increased, the period of oscillation increases, but the amplitude does not change significantly. Increasing the number of phosphorylation sites enhances both the period and amplitude.

Theoretical modeling in this work propose that multisite protein phosphorylation/dephosphorylation could be utilized as a potential module in synthetic oscillators. The main advantages of this synthetic oscillator are: (i) The frequency of oscillation could be adjusted easily by adjusting the ratio of enzymes and substrate, and (ii) The amplitude of oscillation can be adjusted by manipulation of the phosphorylation sites.