How is cryo-EM advancing structural enzymology?

Cryo-EM enables structural enzymology breakthroughs impossible with crystallography. Advantages: no crystallization required (membrane proteins, large complexes), capture of multiple conformational states (3D classification reveals heterogeneity), near-native conditions (avoiding crystal packing artifacts), and smaller sample amounts. Applications: visualizing enzyme catalytic cycles by trapping intermediates, understanding allostery through conformational populations, characterizing macromolecular machines (ribosomes, spliceosome, proteasome), and membrane-bound enzyme complexes (respiratory chain, ATP synthase). Technical considerations: sample preparation (ice thickness, orientation distribution), data collection strategies, image processing for heterogeneous datasets. Limitations include resolution for small proteins (<100 kDa challenging) and dynamic regions. Time-resolved cryo-EM captures millisecond reaction intermediates, approaching real-time enzymology.