MS09-P15 Helicobacter pylori Urease Structures by Cryo-EM and X-ray Crystallography Eva Cunha (Structural Biology and Drug Discovery Group, Norwegian Centre for Molecular Medicine (NCMM), Nordic EMBL Partnership, University of Oslo, Oslo, Norway) Xiaorui Chen (University of California, Irvine, Irvine, United States of America) Hartmut Luecke (Structural Biology and Drug Discovery Group, Norwegian Centre for Molecular Medicine (NCMM), Nordic EMBL Partnership, University of Oslo, Oslo, Norway)email: eva.cunha@ncmm.uio.noHalf the world’s population is chronically infected with Helicobacter pylori, causing gastritis, gastric ulcers and being the major risk factor for gastric adenocarcinoma.  H. pylori’s urease and proton-gated inner-membrane urea channel, HpUreI, are essential for pathogen survival in the acidic environment of the stomach.  The channel is closed at neutral pH and opens at acidic pH to allow the rapid access of urea to cytoplasmic urease.  Urease produces NH3 and CO2, neutralizing entering protons and thus buffering the periplasm to a pH of roughly 6.1 even in gastric juice at a pH near 2.  The urease crystal structures show a 1.1 MDa dodecameric assembly composed of two different subunits, α and β, 61.7 kDa and 26.5 kDa, respectively. The dodecamer is arranged in four copies of the trimeric (α,β)3 unit, resulting in a tetrahedral complex.  Superposition of uninhibited and acetohydroxamic acid-inhibited crystal structures reveals a flap motion of a helix-turn-helix motif at residues α313–α346.  When the inhibitor is bound, the flap moves outwards, creating an opening to the active site, whereas in the absence of the inhibitor the flap is closed, preventing access to the active site.
The recent “resolution revolution” in cryo­EM, driven by developments in instrumentation such as direct detectors, coupled with major improvements in data analysis, has put Cryo-EM at the forefront of structural biology for attaining high-resolution models in close-to-native conditions.  Since 2015, several records have been achieved with the highest resolution structure reported so far for glutamate dehydrogenase (soluble protein, 1.8 Å), anthrax toxin (membrane protein, 2.9 Å) and hemoglobin (only 64 kDa, 3 Å).  We have determined the structure of H. pylori urease using cryo-EM to a resolution of 3.1 Å and we compare it with the previously determined crystal structures.

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Keywords: Helicobacter pylori, Urease, Cryo-EM