Tertiary and Quaternary Structure Organization in GMP Synthetases: Implications for Catalysis

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• Glutamine amidotransferases (GATases) are modular enzymes essential for nitrogen transfer in metabolic pathways.
• Guanosine monophosphate synthetase (GMPS) utilizes GATase activity for de novo purine nucleotide biosynthesis.
• PfGMPS structure reveals large-scale domain rotation linked to catalysis and ammonia channeling.

Purpose of the Study:

• To investigate the structural consequences of mutations in Plasmodium falciparum GMPS.
• To elucidate the relationship between domain rotation, dimer stability, and catalytic activity.
• To identify novel catalytic motifs in GMPS.

Main Methods:

• X-ray crystallography of a C89A/C113A PfGMPS double mutant.
• Structural analysis of domain movement and dimer interface.
• Identification and characterization of conserved sequence motifs.

Main Results:

• An unusual structural variation was observed in the C89A/C113A PfGMPS mutant, exhibiting increased domain rotation.
• This enhanced domain rotation led to the dissociation of the dimeric GMPS structure.
• A previously unrecognized catalytic signature motif was identified.

Conclusions:

• Domain rotation in PfGMPS is a critical factor influencing both its catalytic mechanism and quaternary structure.
• Mutations can disrupt GMPS dimerization and alter catalytic function through significant domain rearrangements.
• The identified motif offers new insights into the catalytic intricacies of glutamine amidotransferases.