Journal
NATURE CHEMICAL BIOLOGY
Volume 7, Issue 12, Pages 950-958Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NCHEMBIO.693
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Funding
- US National Institutes of Health (NIH) [GM54403, P41 RR001081]
- Swedish Research Council
- Swedish Cancer Society
- Wenner-Gren Foundations
- Swedish Foundation for Strategic Research
- National Science Foundation, Division of Biological Infrastructure [DBI-0100085]
- Canadian Institutes for Health Research
- Canadian Foundation for Innovation, Genome Canada through the Ontario Genomics Institute
- GlaxoSmithKline
- Karolinska Institutet
- Knut and Alice Wallenberg Foundation
- Ontario Innovation Trust
- Ontario Ministry for Research and Innovation
- Merck Co., Inc.
- Novartis Research Foundation
- Swedish Agency for Innovation Systems
- Wellcome Trust
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Inosine monophosphate dehydrogenase (IMPDH) and guanosine monophosphate reductase (GMPR) belong to the same structural family, share a common set of catalytic residues and bind the same ligands. The structural and mechanistic features that determine reaction outcome in the IMPDH and GMPR family have not been identified. Here we show that the GMPR reaction uses the same intermediate E-XMP star as IMPDH, but in this reaction the intermediate reacts with ammonia instead of water. A single crystal structure of human GMPR type 2 with IMP and NADPH fortuitously captures three different states, each of which mimics a distinct step in the catalytic cycle of GMPR. The cofactor is found in two conformations: an 'in' conformation poised for hydride transfer and an 'out' conformation in which the cofactor is 6 angstrom from IMP. Mutagenesis along with substrate and cofactor analog experiments demonstrate that the out conformation is required for the deamination of GMP. Remarkably, the cofactor is part of the catalytic machinery that activates ammonia.
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