Structural basis of human PRPS2 filaments

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• 5-phosphate ribose-1-pyrophosphate (PRPP) is a vital metabolite synthesized by PRPP synthase (PRPS).
• Human PRPS has three isoforms (hPRPS1, hPRPS2, hPRPS3), with hPRPS2 showing distinct regulatory properties and cancer relevance.
• PRPS proteins can polymerize into cytoophidia, a mechanism linked to protein function.

Purpose of the Study:

• To investigate the function and polymerization mechanism of human PRPS2 (hPRPS2).
• To determine the structural basis of hPRPS2 polymerization and its regulation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to solve the polymer structure of hPRPS2.
• Biochemical assays were performed to assess the catalytic activity of wild-type and mutant hPRPS2.
• Structural analysis focused on ADP binding and inter-hexamer interactions.

Main Results:

• The hexameric structure of hPRPS2 was determined at 3.08 Å resolution, revealing polymerization into filaments.
• ADP binding at both allosteric and catalytic sites promotes hPRPS2 hexamer stacking into polymers.
• A specific point mutation disrupting inter-hexamer contacts abolished polymerization and significantly decreased catalytic activity.

Conclusions:

• hPRPS2 polymerization is regulated differently compared to bacterial PRPS (ecPRPS).
• The study provides structural insights into hPRPS2 regulation through polymerization.
• Findings highlight the importance of hPRPS2 polymerization for its enzymatic function.