TY - JOUR T1 - Using cryo-EM to map small ligands on dynamic metabolic enzymes: Studies with glutamate dehydrogenase JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.116.103382 SP - mol.116.103382 AU - Mario J. Borgnia AU - Soojay Banerjee AU - Alan Merk AU - Doreen Matthies AU - Alberto Bartesaghi AU - Prashant Rao AU - Jason Pierson AU - Lesley A. Earl AU - Veronica Falconieri AU - Sriram Subramaniam AU - Jacqueline L. S. Milne Y1 - 2016/01/01 UR - http://molpharm.aspetjournals.org/content/early/2016/04/04/mol.116.103382.abstract N2 - Cryo-EM methods are rapidly being used to determine structures at near-atomic resolution, and have great promise in molecular pharmacology, especially in the context of mapping the binding of small molecule ligands to protein complexes that display conformational flexibility. We illustrate this here using glutamate dehydrogenase (GDH), a 330 kDa metabolic enzyme that catalyzes the oxidative deamination of glutamate. Dysregulation of GDH leads to a variety of metabolic and neurological disorders. Here, we report near-atomic resolution cryo-EM structures, at resolutions ranging from 3.2 Å to 3.6 Å for GDH complexes, including complexes for which crystal structures are not available. We show that the binding of the coenzyme NADH alone or in concert with GTP results in a binary mixture in which the enzyme is in either an "open" or "closed" state. While the structure of NADH in the active site is similar between the open and closed states, it is unexpectedly different at the regulatory site. Our studies thus demonstrate that even in instances where there is considerable structural information available from X-ray crystallography, cryo-EM methods can provide useful complementary insights into regulatory mechanisms for dynamic protein complexes. ER -