Inhibition of Escherichia coli glucosamine-6-phosphate synthase by reactive intermediate analogues. The role of the 2-amino function in catalysis.
Glucosamine-6-phosphate synthase (GlmS) catalyzes the formation of D-glucosamine 6-phosphate from D-fructose 6-phosphate using L-glutamine as the ammonia source. Because N-acetylglucosamine is an essential building block of both bacterial cell walls and fungal cell wall chitin, the enzyme is a potential target for antibacterial and antifungal agents. The most potent carbohydrate-based inhibitor of GlmS reported to date is 2-amino-2-deoxy-D-glucitol 6-phosphate, an analogue of the putative cis-enolamine intermediate formed during catalysis. The interaction of a series of structurally related cis-enolamine intermediate analogues with GlmS is described. Although arabinose oxime 5-phosphate is identified as a good competitive inhibitor of GlmS with an inhibition constant equal to 1. 2 (+/-0.3) mM, the presence of the amino function at the 2-position is shown to be important for potent inhibition. Comparison of the binding affinities of 2-deoxy-D-glucitol 6-phosphate and 2-amino-2-deoxy-D-glucitol 6-phosphate indicates that the amino function contributes -4.1 (+/-0.1) kcal/mol to the free energy of inhibitor binding. Similarly, comparison of the binding affinities of 2-deoxy-D-glucose 6-phosphate and D-glucosamine 6-phosphate indicates that the amino function contributes -3.0 (+/-0.1) kcal/mol to the free energy of product binding. Interactions between GlmS and the 2-amino function of its ligands contribute to the uniform binding of the product and the cis-enolamine intermediate as evidenced by the similar contribution of the amino group to the free energy of binding of D-glucosamine 6-phosphate and 2-amino-2-deoxy-D-glucitol 6-phosphate, respectively.
Bearne
S L
SL
Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada.
Blouin
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D020134:Catalytic Domain; D004926:Escherichia coli / Q000201:enzymology*; D005944:Glucosamine / Q000031:analogs & derivatives / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives / Q000378:metabolism; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000037:antagonists & inhibitors* / Q000737:chemistry; D008958:Models, Molecular; D010091:Oximes / Q000378:metabolism; D013012:Sorbitol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D013403:Sugar Phosphates / Q000737:chemistry / Q000378:metabolism*
C099009:2-deoxy-2-aminoglucitol-6-phosphate; C403168:2-deoxyglucitol 6-phosphate; D010091:Oximes; D013403:Sugar Phosphates; C403169:arabinose oxime 5-phosphate; C001293:glucosamine 6-phosphate; D013012:Sorbitol; D019298:Glucose-6-Phosphate; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D005944:Glucosamine