The nucleotide-binding site of Aquifex aeolicus LpxC

The structure of recombinant Aquifex aeolicus UDP-3-O-acyl-N-acetylglucosamine deacetylase (LpxC) in complex with UDP has been determined to a resolution of 2.2 angstrom. Previous studies have characterized the binding sites of the fatty-acid and sugar moieties of the substrate, UDP-(3-O-hydroxymyristoyl)-N--acetylglucosamine, but not that of the nucleotide. The uracil-binding site is constructed from amino acids that are highly conserved across species. Hydrophobic associations with the Phe155 and Arg250 side chains in combination with hydrogen-bonding interactions with the main chain of Glu154 and the side chains of Tyr151 and Lys227 position the base. The phosphate and ribose groups are directed away from the active site and interact with Arg137, Lys156, Glu186 and Arg250. The orientation of the phosphate-ribose tail is not conducive to catalysis, perhaps owing to the position of an inhibitory Zn2+. However, based on the position of uracil revealed in this study and on the previously reported complex of LpxC with an inhibitor, a model is proposed for substrate binding.