Cofactor mobility determines reaction outcome in the IMPDH and GMPR (β-α)8 barrel enzymes.
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* 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 Å 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.
Department of Biology, Brandeis University, Waltham, Massachusetts, USA.
Gregory C
GC
Patton
Pål
P
Stenmark
Deviprasad R
DR
Gollapalli
Robin
R
Sevastik
Petri
P
Kursula
Susanne
S
Flodin
Herwig
H
Schuler
Colin T
CT
Swales
Hans
H
Eklund
Fahmi
F
Himo
Pär
P
Nordlund
Lizbeth
L
Hedstrom
D055162:Biocatalysis; D018360:Crystallography, X-Ray; D050899:GMP Reductase / Q000737:chemistry / Q000378:metabolism*; D006157:Guanosine Monophosphate / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007168:IMP Dehydrogenase / Q000737:chemistry / Q000378:metabolism*; D007291:Inosine Monophosphate / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D009249:NADP / Q000737:chemistry / Q000378:metabolism; D011789:Quantum Theory; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism
D013438:Sulfhydryl Compounds; D007291:Inosine Monophosphate; D009249:NADP; D006157:Guanosine Monophosphate; D007168:IMP Dehydrogenase; D050899:GMP Reductase; C469406:GMPR2 protein, human