Implementing lattice ultrasensitivity in E. coli chemotaxis

Amplification of weak signals is a vital step in many biological processes. In zero-order ultrasensitivity, described already in 1981, amplification arises through the opposed modifications of two enzymes operating at saturation on a single substrate. The enzymes and substrate are assumed to be reacting in a well-mixed solution. In contrast, the proteins involved in the first steps of E. coli chemosensing and signal amplification exist in a stable lattice in the membrane. Here, we present a mechanism for this signal amplification which is analogous to zero-order ultrasensitivity but emerges through local non-equilibrium interactions on a lattice. Based on known or supposed protein interactions in the lattice, we implement a dynamics where sites of the lattice are either active or inactive, and activity and inactivity can spread through the lattice. This specific molecular implementation of signal amplification makes predictions for experiments and help to illuminate the specific role of dissipation in the signaling process.