Structure and catalytic mechanism of glucosamine 6-phosphate deaminase from Escherichia coli at 2.1 A resolution.
BACKGROUND
Glucosamine 6-phosphate deaminase from Escherichia coli is an allosteric hexameric enzyme which catalyzes the reversible conversion of D-glucosamine 6-phosphate into D-fructose 6-phosphate and ammonium ion and is activated by N-acetyl-D-glucosamine 6-phosphate. Mechanistically, it belongs to the group of aldoseketose isomerases, but its reaction also accomplishes a simultaneous amination/deamination. The determination of the structure of this protein provides fundamental knowledge for understanding its mode of action and the nature of allosteric conformational changes that regulate its function.


RESULTS
The crystal structure of glucosamine 6-phosphate deaminase with bound phosphate ions is presented at 2.1 A resolution together with the refined structures of the enzyme in complexes with its allosteric activator and with a competitive inhibitor. The protein fold can be described as a modified NAD-binding domain.


CONCLUSIONS
From the similarities between the three presented structures, it is concluded that these represent the enzymatically active R state conformer. A mechanism for the deaminase reaction is proposed. It comprises steps to open the pyranose ring of the substrate and a sequence of general base-catalyzed reactions to bring about isomerization and deamination, with Asp72 playing a key role as a proton exchanger.
Oliva
G
G
Instituto de Fisica de São Carlos, Universidade de São Paulo, Brazil.
Fontes
M R
MR
Garratt
R C
RC
Altamirano
M M
MM
Calcagno
M L
ML
Horjales
E
E
D019747:Aldose-Ketose Isomerases; D000494:Allosteric Regulation; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D002238:Carbohydrate Epimerases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology*; D005636:Fructosephosphates / Q000096:biosynthesis; D005944:Glucosamine / Q000031:analogs & derivatives / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives*; D005958:Glucosephosphates / Q000378:metabolism; D046911:Macromolecular Substances; D008958:Models, Molecular; D009243:NAD / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D011487:Protein Conformation; D013012:Sorbitol / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D013403:Sugar Phosphates / Q000737:chemistry / Q000494:pharmacology
C099009:2-deoxy-2-aminoglucitol-6-phosphate; D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D005636:Fructosephosphates; D005958:Glucosephosphates; D046911:Macromolecular Substances; D010710:Phosphates; D013403:Sugar Phosphates; D009243:NAD; C001293:glucosamine 6-phosphate; D013012:Sorbitol; D019298:Glucose-6-Phosphate; C027618:fructose-6-phosphate; C020582:glucosamine-6-phosphate isomerase; D002238:Carbohydrate Epimerases; D019747:Aldose-Ketose Isomerases; D005944:Glucosamine