Steve Ealick's Research Group


ADP-L-glycero-D-mannoheptose 6-epimerase


PDB file: 1EQ2

Description:

ADP-L-glycero-D-mannoheptose 6-epimerase (AGME) is required for lipopolysaccharide (LPS) biosynthesis in most genera of pathogenic and non-pathogenic Gram-negative bacteria. It catalyzes the interconversion of ADP-D-glycero-D-mannoheptose and ADP-L-glycero-D-mannoheptose, a precursor of the seven-carbon sugar L-glycero-D-mannoheptose (heptose). The structure of AGME, in complex with NADP and the catalytic inhibitor ADP-glucose, has been determined at 2.0 Å resolution by multiwavelength anomalous diffraction (MAD) phasing methods.

 

Each monomer comprises two domains: a large N-terminal domain, consisting of a modified seven-stranded Rossmann fold that is associated with NADP binding; and a smaller C-terminal domain which consists of a small αβ domain that is involved in the substrate binding. NADP and ADP-glucose are modeled in the ball-and-stick representations.

 

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AGME is a homopentameric enzyme, which crystallizes with two pentamers in the asymmetric unit. The location of 70 crystallographically independent selenium sites was a key step in the structure determination process. Each monomer comprises two domains: a large N-terminal domain, consisting of a modified seven-stranded Rossmann fold that is associated with NADP binding; and a smaller C-terminal domain which is involved in substrate binding.

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The NADP-binding site of AGME is located at the topological switch point of the N-terminal domain modified fold. The ADP glucose-binding-site is characterized by strong hydrophobic interactions at the adenine base. Stacking interactions sandwich the base between Phe201 and Phe243. In each of these figures, shaded boxes represent hydrophobic contacts. Potential hydrogen bonds are indicated by dashed lines with distances given in Å.

References:

Deacon AM, Ni YS, Coleman WG Jr., and Ealick SE. The Crystal Structure of ADP-L-glycero-D-mannoheptose 6-epimerase: Catalysis with a Twist. Structure 8:453-462 (2000).

Ding L, Zhang Y, Deacon AM, Ealick SE, Ni Y, Sun P, and Coleman WG Jr. Crystallization and preliminary X-ray diffraction studies of the lipopolysaccharide core biosynthetic enzyme ADP-L-glycero-D-mannoheptose 6-epimerase from Escherichia coli K-12. Acta Crystallogr. D 55:685-688 (1999).

Ni Y, McPhie P, Deacon AM, Ealick S, and Coleman WG, Jr. Evidence that NADP+ is the physiological cofactor of ADP-L-glycero-D-mannoheptose 6-epimerase. J. Biol. Chem. 276:27329-27334 (2001).



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