Reaction-based cryo-EM resolves the continuous conformational spectrum of CTP synthase catalysis.

Reaction-based cryo-EM reveals a continuous conformational spectrum of Drosophila melanogaster CTPS during catalysis, capturing dynamic enzyme states with allosteric effectors.

• Why it matters: Understanding enzyme conformational changes under native turnover conditions is a major challenge in structural biology, limiting insights into catalysis mechanisms and regulation.
• What they did: The authors developed a reaction-based cryo-EM approach combined with 3D variability analysis to sample actively catalyzing CTPS with natural substrates and effectors, visualizing the chemical progression and co-occupancy patterns.
• The result: This method uncovers a chemically annotated conformational landscape, demonstrating that UTP phosphorylation by ATP shifts CTPS toward more closed states, enabling detailed insights into enzyme dynamics without trapping specific intermediates.