Overlaid positive and negative feedback loops shape dynamical properties of PhoPQ two-component system
Fig 4
Understanding the biphasic dose-response possible in the two-state model of PhoPQ.
A—Reactions in PhoPQ-MgrB network. Dotted squares enclose 4 sub forms of PhoQ (Qph, Qkin, QBph, QBkin). 4 reactions outside the dotted squares have rates comparable to dilution due to growth. Each sub form dilutes with a rate kpd, while synthesis is only in the Q* form. B—Most significant fluxes at high Mg2+. Steady state [PhoP-P] is approximated by matching phosphorylation and dephosphorylation fluxes. Phosphorylation flux is proportional to 1/k−1, while dephosphorylation flux is approximately constant. C- Most significant fluxes at intermediate Mg2+. Phosphorylation flux is proportional to [B]Total and independent of k−1 while dephosphorylation flux is still approximately constant D- [PhoP-P] as a function of signal showing plateau at intermediate Mg2+. Blue line indicates simulated [PhoP-P] from the model in the previous section. Red dashed line shows approximate [PhoP-P] in the high Mg2+ range, and black dashed line shows the approximate plateau value of [PhoP-P] in the intermediate Mg2+ range. E- Fractions of total Q in the 4 catalytic forms.