title: Neutron structure of the cyclic glucose-bound xylose isomerase E186Q mutant.
abstract: Ketol-isomerases catalyze the reversible isomerization between aldoses and ketoses. D-Xylose isomerase carries out the first reaction in the catabolism of D-xylose, but is also able to convert D-glucose to D-fructose. The first step of the reaction is an enzyme-catalyzed ring opening of the cyclic substrate. The active-site amino-acid acid/base pair involved in ring opening has long been investigated and several models have been proposed. Here, the structure of the xylose isomerase E186Q mutant with cyclic glucose bound at the active site, refined against joint X-ray and neutron diffraction data, is reported. Detailed analysis of the hydrogen-bond networks at the active site of the enzyme suggests that His54, which is doubly protonated, is poised to protonate the glucose O5 position, while Lys289, which is neutral, promotes deprotonation of the glucose O1H hydroxyl group via an activated water molecule. The structure also reveals an extended hydrogen-bonding network that connects the conserved residues Lys289 and Lys183 through three structurally conserved water molecules and residue 186, which is a glutamic acid to glutamine mutation.
authors: Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors: Parthapratim
authors: P
authors: Munshi
authors: Department of Structural Biology, SUNY Buffalo, Hauptman-Woodward Medical Research Institute, Buffalo, NY 14203, USA.
authors: Edward H
authors: EH
authors: Snell
authors: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA.
authors: Mark J
authors: MJ
authors: van der Woerd
authors: Structural Biology, AbbVie Inc., North Chicago, IL 60064, USA.
authors: Russell A
authors: RA
authors: Judge
authors: Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors: Dean A A
authors: DA
authors: Myles
authors: Renz Research Inc., Westmont, IL 60559, USA.
authors: Zhong
authors: Z
authors: Ren
authors: Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors: Flora
authors: F
authors: Meilleur
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D020134:Catalytic Domain; D005947:Glucose / Q000031:analogs & derivatives / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009154:Mutation; D033363:Neutron Diffraction; D011485:Protein Binding; D011487:Protein Conformation; D011522:Protons; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D053838:Scattering, Small Angle; D013302:Streptomyces / Q000737:chemistry* / Q000201:enzymology; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D011522:Protons; D011994:Recombinant Proteins; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase; D005947:Glucose
keywords: E186Q mutant; cyclic glucose; neutron diffraction; xylose isomerase