Low CyaA expression and anti-cooperative binding of cAMP to CRP frames the scope of the cognate regulon of Pseudomonas putida

Although the soil bacterium Pseudomonas putida KT2440 bears a bona fide adenylate cyclase gene (cyaA), intracellular concentrations of 3 ',5 '-cyclic adenosine monophosphate (cAMP) are barely detectable. By using reporter technology and direct quantification of cAMP under various conditions, we show that such low levels of the molecule stem from the stringent regulation of its synthesis, efflux and degradation. Poor production of cAMP was the result of inefficient translation of cyaA mRNA. Moreover, deletion of the cAMP-phosphodiesterase pde gene led to intracellular accumulation of the cyclic nucleotide, exposing an additional cause of cAMP drain in vivo. But even such low levels of the signal sustained activation of promoters dependent on the cAMP-receptor protein (CRP). Genetic and biochemical evidence indicated that the phenomenon ultimately rose from the unusual binding parameters of cAMP to CRP. This included an ultratight cAMP-Crp(P. putida) affinity (K-D of 45.0 +/- 3.4 nM) and an atypical 1:1 effector/dimer stoichiometry that obeyed an infrequent anti-cooperative binding mechanism. It thus seems that keeping the same regulatory parts and their relational logic but changing the interaction parameters enables genetic devices to take over entirely different domains of the functional landscape.

Automated summary

The soil bacterium Pseudomonas putida KT2440 has low intracellular levels of 3',5'-cyclic adenosine monophosphate (cAMP) due to stringent regulation of its synthesis, efflux, and degradation. Despite this, the low levels of cAMP sustain activation of certain promoters dependent on the cAMP-receptor protein (CRP) through unusual binding parameters of cAMP to CRP. This suggests that altering interaction parameters can enable genetic devices to take over different domains of the functional landscape while retaining the same regulatory parts and logic.