AMPylation is involved in bacterial homeostasis. The most famous example is AMPylator GS-ATase (GlnE), which contributes in complex regulation of nitrogen metabolism through AMPylation of glutamine synthetase that was introduced in the AMPylation and DeAMPylation parts.
Another example of AMPylators that play a role in bacterial homeostasis is the class I Fic AMPylators (FicT), which modifies the GyrB subunit of DNA gyrase, the conserved tyrosine residue for ATP binding of ParE subunit at Topoisomerase IV. This DNA gyrase inactivation by AMPylation leads to the activation of SOS response, which is the cellular response to DNA damage. The activity of FicT AMPylation is reversible and only leads to growth arrest, but not cell death. Therefore, FicT AMPylation plays a role in regulating cell stress, which is shown in the Wolbachia bacteria that the level of FicT increases in response to doxycycline.
A Class III Fic AMPylator NmFic of N. meningtidis is also found to modify AMPylate GyrB at the conserved tyrosine for ATP binding. This shows that Fic domains are highly conserved that indicates the important role of AMPylation in regulating cellular stress in bacteria. The regulation of NmFic involves the concentration-dependent monomerization and autoAMPylation for activation of NmFic activity.