Fig. 1.

A. Alternative network designs for classical TCS modules.

B. SK denotes the unphosphorylated sensor kinase, and RR the unphosphorylated response regulator; phosphorylated forms of these proteins are denoted as SK∼P and RR∼P, respectively. The left-hand side of the panel represents a monofunctional design, in which SK∼P phosphorylates the RR and the dephosphorylation of the RR∼P is catalysed by an alternative phosphatase. The right-hand side of the panel represents a bifunctional design, in which the SK∼P phosphorylates the RR and the SK dephosphorylates the RR∼P. Schematic representation of graded (monostable, solid line) and hysteretic (bistable, dashed line) responses.

C. Reaction scheme for a generic two-component system. For simplicity, the release of inorganic phosphate is not depicted and the mechanistic details of the alternative phosphatase (Ph) reactions are omitted. See Table 1 for details on how the use of different values for the parameters of this scheme allows us to model the alternative designs shown in (A). Period (.) denotes protein binding complex.