Non-Equilibrium Phase Transitions in Biomolecular Signal Transduction

Feb 23, 2011, 11:00 AM
45m
FB42 (AlbaNova Main Building)

FB42

AlbaNova Main Building

Speaker

Supriya Krishnamurthy (KTH and Stockholm University)

Description

We study the stochastic switching behavior of a model circuit of multisite phosphorylation and dephosphorylation with feedback. The circuit consists of a kinase and phosphatase acting on multiple sites of a substrate that, contingent on its modification state, catalyzes its own phosphorylation and, in a symmetric scenario, dephosphorylation. The symmetric case is viewed as a cartoon of conflicting feedback that could result from antagonistic pathways impinging on the state of a shared component.
We find that multisite phosphorylation is sufficient for bistable behavior under feedback even when catalysis is linear in substrate concentration. Bistability occurs as either a first-order or second-order non-equilibrium phase transition, depending on the network symmetries and the ratio of phosphatase to kinase numbers. We also find that the number of substrate molecules is a key parameter controlling the onset of the bistable regime, fluctuation intensity, and the residence time in a switched state. We compute the phase diagram, fluctuation spectrum and large-deviation properties related to switch memory using functional integral methods from reaction-diffusion theory.

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