The Rel stringent factor from Thermus thermophilus: crystallization and X-ray analysis

Area of Science:

• Bacterial Physiology
• Molecular Biology
• Structural Biology

Background:

• The stringent response, regulated by (p)ppGpp, is essential for bacterial adaptation to stress, influencing survival and virulence.
• RelA/SpoT homologue (RSH) enzymes control (p)ppGpp levels through opposing pyrophosphorylation and pyrophosphatase activities.
• Bifunctional Rel enzymes present crystallization challenges due to instability and aggregation, hindering structural and functional studies.

Purpose of the Study:

• To produce and biochemically characterize the bifunctional catalytic region of the Thermus thermophilus Rel stringent factor (Rel_Tt^NTD).
• To determine the crystal structures of Rel_Tt^NTD in its resting state and bound to nucleotides.
• To overcome the inherent instability of bifunctional Rel enzymes for structural studies.

Main Methods:

• Production and purification of Rel_Tt^NTD.
• Biochemical assays to assess enzyme activity and stability.
• Crystallization screening and X-ray diffraction data collection.
• Structural analysis of crystallized Rel_Tt^NTD.

Main Results:

• Rel_Tt and its catalytic domain (Rel_Tt^NTD) were produced and biochemically analyzed.
• Monomeric Rel_Tt and Rel_Tt^NTD were stabilized by Mn²⁺ and mellitic acid.
• Rel_Tt^NTD crystallized in two different space groups (P4₁22 and P4₁2₁2) at different temperatures (4°C and 20°C, respectively).

Conclusions:

• The study successfully produced and stabilized the Rel stringent factor from Thermus thermophilus, enabling structural determination.
• The findings provide insights into the structural basis of stringent response regulation in bacteria.
• This work facilitates further investigation into the mechanism of Rel enzymes and potential therapeutic targets.