pH-dependent gating mechanism of the Helicobacter pylori urea channel revealed by cryo-EM.

The urea channel of Helicobacter pylori (HpUreI) is an ideal drug target for preventing gastric cancer but incomplete understanding of its gating mechanism has hampered development of inhibitors for the eradication of H. pylori. Here, we present the cryo-EM structures of HpUreI in closed and open conformations, both at a resolution of 2.7 Å. Our hexameric structures of this small membrane protein (~21 kDa/protomer) resolve its periplasmic loops and carboxyl terminus that close and open the channel, and define a gating mechanism that is pH dependent and requires cooperativity between protomers in the hexamer. Gating is further associated with well-resolved changes in the channel-lining residues that modify the shape and length of the urea pore. Site-specific mutations in the periplasmic domain and urea pore identified key residues important for channel function. Drugs blocking the urea pore based on our structures should lead to a new strategy for H. pylori eradication

Structure of the proton-gated urea channel from the gastric pathogen Helicobacter pylori.

Half the world's population is chronically infected with Helicobacter pylori, causing gastritis, gastric ulcers and an increased incidence of gastric adenocarcinoma. Its proton-gated inner-membrane urea channel, HpUreI, is essential for 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 NH(3) and CO(2), neutralizing entering protons and thus buffering the periplasm to a pH of roughly 6.1 even in gastric juice at a pH below 2.0. Here we report the structure of HpUreI, revealing six protomers assembled in a hexameric ring surrounding a central bilayer plug of ordered lipids. Each protomer encloses a channel formed by a twisted bundle of six transmembrane helices. The bundle defines a previously unobserved fold comprising a two-helix hairpin motif repeated three times around the central axis of the channel, without the inverted repeat of mammalian-type urea transporters. Both the channel and the protomer interface contain residues conserved in the AmiS/UreI superfamily, suggesting the preservation of channel architecture and oligomeric state in this superfamily. Predominantly aromatic or aliphatic side chains line the entire channel and define two consecutive constriction sites in the middle of the channel. Mutation of Trp 153 in the cytoplasmic constriction site to Ala or Phe decreases the selectivity for urea in comparison with thiourea, suggesting that solute interaction with Trp 153 contributes specificity. The previously unobserved hexameric channel structure described here provides a new model for the permeation of urea and other small amide solutes in prokaryotes and archaea

Microwave Spin-Pumping from an Antiferromagnet FeBO3

Recently, canted antiferromagnets offer great potential for fundamental research and applications due to their unique properties. The presence of the Dzyaloshinskii-Moriya interaction leads to the existence of a weak ferromagnetic moment at room temperature. We study both theoretically and experimentally microwave spin pumping by the quasi-ferromagnetic mode from a canted easy plane antiferromagnet with weak ferromagnetism FeBO3. The conversion of a microwave signal into the constant voltage is realized using the inverse spin Hall effect in an iron borate/heavy metal heterostructure. We use an additional bias magnetic field to selectively tune the resonance frequency of such a microwave detector over a wide range up to 43.5 GHz with potential sensitivity near 2.5 microV/W. We confirm the pure spin current nature by changing polarity of the detected via inverse spin Hall effect voltage by switching the direction of the bias magnetic field. We believe that our results will be useful for the development of highly tunable, portable and sensitive microwave antiferromagnet-based functional devices.Comment: 7 pages, 3 figures, 3 pages supplementary informatio

Structure of human cytomegalovirus virion reveals host tRNA binding to capsid-associated tegument protein pp150.

Under the Baltimore nucleic acid-based virus classification scheme, the herpesvirus human cytomegalovirus (HCMV) is a Class I virus, meaning that it contains a double-stranded DNA genome-and no RNA. Here, we report sub-particle cryoEM reconstructions of HCMV virions at 2.9 Å resolution revealing structures resembling non-coding transfer RNAs (tRNAs) associated with the virion's capsid-bound tegument protein, pp150. Through deep sequencing, we show that these RNA sequences match human tRNAs, and we built atomic models using the most abundant tRNA species. Based on our models, tRNA recruitment is mediated by the electrostatic interactions between tRNA phosphate groups and the helix-loop-helix motif of HCMV pp150. The specificity of these interactions may explain the absence of such tRNA densities in murine cytomegalovirus and other human herpesviruses

Structure of human cytomegalovirus virion reveals host tRNA binding to capsid-associated tegument protein pp150.

Under the Baltimore nucleic acid-based virus classification scheme, the herpesvirus human cytomegalovirus (HCMV) is a Class I virus, meaning that it contains a double-stranded DNA genome-and no RNA. Here, we report sub-particle cryoEM reconstructions of HCMV virions at 2.9 Å resolution revealing structures resembling non-coding transfer RNAs (tRNAs) associated with the virion's capsid-bound tegument protein, pp150. Through deep sequencing, we show that these RNA sequences match human tRNAs, and we built atomic models using the most abundant tRNA species. Based on our models, tRNA recruitment is mediated by the electrostatic interactions between tRNA phosphate groups and the helix-loop-helix motif of HCMV pp150. The specificity of these interactions may explain the absence of such tRNA densities in murine cytomegalovirus and other human herpesviruses

pH-dependent gating mechanism of the Helicobacter pylori urea channel revealed by cryo-EM.

The urea channel of Helicobacter pylori (HpUreI) is an ideal drug target for preventing gastric cancer but incomplete understanding of its gating mechanism has hampered development of inhibitors for the eradication of H. pylori. Here, we present the cryo-EM structures of HpUreI in closed and open conformations, both at a resolution of 2.7 Å. Our hexameric structures of this small membrane protein (~21 kDa/protomer) resolve its periplasmic loops and carboxyl terminus that close and open the channel, and define a gating mechanism that is pH dependent and requires cooperativity between protomers in the hexamer. Gating is further associated with well-resolved changes in the channel-lining residues that modify the shape and length of the urea pore. Site-specific mutations in the periplasmic domain and urea pore identified key residues important for channel function. Drugs blocking the urea pore based on our structures should lead to a new strategy for H. pylori eradication

Structure of the proton-gated urea channel from the gastric pathogen Helicobacter pylori.

Half the world's population is chronically infected with Helicobacter pylori, causing gastritis, gastric ulcers and an increased incidence of gastric adenocarcinoma. Its proton-gated inner-membrane urea channel, HpUreI, is essential for 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 NH(3) and CO(2), neutralizing entering protons and thus buffering the periplasm to a pH of roughly 6.1 even in gastric juice at a pH below 2.0. Here we report the structure of HpUreI, revealing six protomers assembled in a hexameric ring surrounding a central bilayer plug of ordered lipids. Each protomer encloses a channel formed by a twisted bundle of six transmembrane helices. The bundle defines a previously unobserved fold comprising a two-helix hairpin motif repeated three times around the central axis of the channel, without the inverted repeat of mammalian-type urea transporters. Both the channel and the protomer interface contain residues conserved in the AmiS/UreI superfamily, suggesting the preservation of channel architecture and oligomeric state in this superfamily. Predominantly aromatic or aliphatic side chains line the entire channel and define two consecutive constriction sites in the middle of the channel. Mutation of Trp 153 in the cytoplasmic constriction site to Ala or Phe decreases the selectivity for urea in comparison with thiourea, suggesting that solute interaction with Trp 153 contributes specificity. The previously unobserved hexameric channel structure described here provides a new model for the permeation of urea and other small amide solutes in prokaryotes and archaea

In Search of Small Molecules That Selectively Inhibit MBOAT4.

Ghrelin is a 28-residue peptide hormone produced by stomach P/D1 cells located in oxyntic glands of the fundus mucosa. Post-translational octanoylation of its Ser-3 residue, catalyzed by MBOAT4 (aka ghrelin O-acyl transferase (GOAT)), is essential for the binding of the hormone to its receptor in target tissues. Physiological roles of acyl ghrelin include the regulation of food intake, growth hormone secretion from the pituitary, and inhibition of insulin secretion from the pancreas. Here, we describe a medicinal chemistry campaign that led to the identification of small lipopeptidomimetics that inhibit GOAT in vitro. These molecules compete directly for substrate binding. We further describe the synthesis of heterocyclic inhibitors that compete at the acyl coenzyme A binding site