(p)ppGpp Regulates a Bacterial Nucleosidase by an Allosteric Two-Domain Switch

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The stringent response is crucial for bacterial adaptation to environmental changes.
• Alarmones like guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp) regulate this response.
• PpnN (YgdH) in Escherichia coli is a nucleosidase involved in purine homeostasis and binds (p)ppGpp.

Purpose of the Study:

• To investigate the role of (p)ppGpp in regulating PpnN activity.
• To elucidate the structural basis for (p)ppGpp binding and its effect on PpnN.
• To understand the physiological implications of PpnN activity during stress.

Main Methods:

• In vitro and in vivo enzymatic assays.
• Structural analysis of PpnN.
• Assessment of bacterial fitness and antibiotic tolerance.

Main Results:

• (p)ppGpp was found to stimulate PpnN's catalytic activity.
• The crystal structure of PpnN revealed allosteric (p)ppGpp binding sites and a conformational change upon binding.
• PpnN activity leads to nucleobase accumulation during stress.
• PpnN enhances bacterial fitness and antibiotic tolerance.

Conclusions:

• (p)ppGpp allosterically stimulates PpnN, providing a structural mechanism for enhanced activity.
• PpnN plays a role in bacterial stress adaptation and antibiotic tolerance.
• A model is proposed where PpnN balances nucleotide synthesis and degradation for physiological homeostasis during stress.