Regulation of (p)ppGpp hydrolysis by a conserved archetypal regulatory domain

Sensory and regulatory domains allow bacteria to adequately respond to environmental changes. The regulatory ACT (Aspartokinase, Chorismate mutase and TyrA) domains are mainly found in metabolicrelated proteins as well as in long (p)pp Gpp synthetase/hydrolase enzymes. Here, we investigate the functional role of the ACT domain of SpoT, the only (p)pp Gpp synthetase/hydrolase of Caulobacter crescentus. We show that SpoT requires the ACT domain to efficiently hydrolyze (p)pp Gpp. In addition, our in vivo and in vitro data show that the phosphorylated version of EIIANtr (EIIANtr∼P) interacts directly with the ACT and inhibits the hydrolase activity of SpoT. Finally, we highlight the conservation of the ACT-dependent interaction between EIIANtr∼P and SpoT/Rel along with the phosphotransferase system (PTSNtr)-dependent regulation of (p)pp Gpp accumulation upon nitrogen starvation in Sinorhizobium meliloti, a plant-associated α-proteobacterium. Thus, thiswork suggests that α-proteobacteria might have inherited from a common ancestor, a PTSNtr dedicated to modulate (p)pp Gpp levels in response to nitrogen availability.SCOPUS: ar.j