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

Devastating chest wall necrotizing fasciitis following pigtail catheter drainage

SummaryPigtail catheter for drainage of pleural effusion has gained popularity. Complication related to the insertion of these small-bore catheter is low. In this report, we highlight two cases with devastating necrotizing fasciitis of chest wall following pigtail catheter insertion

Adaptor protein Shc acts as an immune-regulator for the LPS-stimulated maturation of bone marrow-derived dendritic cells

<p>Abstract</p> <p>Background</p> <p>The Shc isoforms is known to mediate immune responses and has been indicated as a negative regulator of autoimmunity and lymphocyte activation. We aimed to evaluate the immune-regulatory role of Shc in rat bone marrow-derived DCs in the maturation process triggered by LPS.</p> <p>Results</p> <p>We found that, in response to LPS, expression of Shc proteins was induced and that neutralization of Shc inhibited the LPS-induced transient phosphorylation of p52Shc on pTyr239/240 in DCs of Lewis (LEW; RT1^l) rats. Moreover, the significantly enhanced expression of IL-10 and the surface level of costimulatory molecule CD80, as well as suppressed expression of IL-6 and IL-12 in the Shc-silenced DCs were also observed. Similar IκB phosphorylation occurred in Shc-silenced DCs primed by LPS, indicating Shc is not associated with NF-κB pathway. We further demonstrate that Shc blockade on LPS-treated DCs results in significant increase of the overall STAT3 phosphorylation and the relative levels of phospho-STAT3 in the nuclear fraction. STAT3 activation by LPS with or without Shc blockade was totally abolished by SU6656, a selective Src family kinases inhibitor, underscoring the critical role of Src-mediated activation.</p> <p>Conclusions</p> <p>We conclude that Shc blockade in LPS-primed DC leads to the development of tolerogenic DC via Src-dependent STAT3 activation and that adaptor protein Shc might play a pivotal role in mediating immunogenic and tolerogenic properties of DCs.</p

Deactivation of TBP contributes to SCA17 pathogenesis

Spinocerebellar ataxia type 17 (SCA17) is an autosomal dominant cerebellar ataxia caused by the expansion of polyglutamine (polyQ) within the TATA box-binding protein (TBP). Previous studies have shown that polyQexpanded TBP forms neurotoxic aggregates and alters downstream genes. However, how expanded polyQ tracts affect the function of TBP and the link between dysfunctional TBP and SCA17 is not clearly understood. In this study, we generated novel Drosophila models for SCA17 that recapitulate pathological features such as aggregate formation, mobility defects and premature death. In addition to forming neurotoxic aggregates, we determined that polyQ-expanded TBP reduces its own intrinsic DNA-binding and transcription abilities. Dysfunctional TBP also disrupts normal TBP function. Furthermore, heterozygous dTbp amorph mutant flies exhibited SCA17-like phenotypes and flies expressing polyQ-expanded TBP exhibited enhanced retinal degeneration, suggesting that loss of TBP function may contribute to SCA17 pathogenesis. We further determined that the downregulation of TBP activity enhances retinal degeneration in SCA3 and Huntington&apos;s disease fly models, indicating that the deactivation of TBP is likely to play a common role in polyQ-induced neurodegeneration

Chronic Kidney Disease Stage Is a Modulator on the Association between High-Sensitivity C-Reactive Protein and Coronary Vasospastic Angina

The prevalence of coronary vasospasm and also the factors associated with coronary vasospasm in CKD is still unclear. In this cross-sectional study of 859 consecutive CKD patients with angina pectoris received coronary catheterization, we evaluated the factors associated with coronary vasospasm. Patients with vasospasm were older and had higher peripheral blood white cell counts, higher peripheral blood monocyte cell counts, higher haemoglobin levels, higher hs-CRP levels, and lower levels of serum creatinine than patients without vasospasm. The results of multivariate logistic regression analysis revealed that peripheral blood monocyte count and hs-CRP level were independently associated with coronary vasospasm in patients with stage 1 CKD. Only peripheral blood monocyte count but not hs-CRP was independently associated with coronary vasospasm in patients with stages 2 and 3 of CKD. In conclusion, peripheral blood monocyte count is independently associated with coronary vasospasm in patients with stage 1–3 CKD, whereas hs-CRP is only independently associated with coronary vasospasm in patients with stage 1 CKD

Trypanosoma cruzi CYP51 Inhibitor Derived from a Mycobacterium tuberculosis Screen Hit

Enzyme sterol 14α-demethylase (CYP51) is a well-established target for anti-fungal therapy and is a prospective target for Chagas' disease therapy. We previously identified a chemical scaffold capable of delivering a variety of chemical structures into the CYP51 active site. In this work the binding modes of several second generation compounds carrying this scaffold were determined in high-resolution co-crystal structures with CYP51 of Mycobacterium tuberculosis. Subsequent assays against CYP51 in Trypanosoma cruzi, the agent of Chagas' disease, demonstrated that two of the compounds bound tightly to the enzyme. Both were tested for inhibitory effects against T. cruzi and the related protozoan parasite Trypanosoma brucei. One of the compounds had potent, selective anti–T. cruzi activity in infected mouse macrophages. This compound is currently being evaluated in animal models of Chagas' disease. Discrimination between T. cruzi and T. brucei CYP51 by the inhibitor was largely based on the variability of a single amino acid residue at a critical position in the active site. Our work is aimed at rational design of potent and highly selective CYP51 inhibitors with potential to become therapeutic drugs. Drug selectivity to prevent host–pathogen cross-reactivity is pharmacologically important, because CYP51 is present in human host

Structural Characterization of CYP51 from Trypanosoma cruzi and Trypanosoma brucei Bound to the Antifungal Drugs Posaconazole and Fluconazole

Chagas Disease is caused by kinetoplastid protozoa Trypanosoma cruzi, whose sterols resemble those of fungi, in both composition and biosynthetic pathway. Azole inhibitors of sterol 14α-demethylase (CYP51), such as fluconazole, itraconazole, voriconazole, and posaconazole, successfully treat fungal infections in humans. Efforts have been made to translate anti-fungal azoles into a second-use application for Chagas Disease. Ravuconazole and posaconazole have been recently proposed as candidates for clinical trials with Chagas Disease patients. However, the widespread use of posaconazole for long-term treatment of chronic infections may be limited by hepatic and renal toxicity, a requirement for simultaneous intake of a fatty meal or nutritional supplement to enhance absorption, and cost. To aid our search for structurally and synthetically simple CYP51 inhibitors, we have determined the crystal structures of the CYP51 targets in T. cruzi and T. brucei, both bound to the anti-fungal drugs fluconazole or posaconazole. The structures provide a basis for a design of new drugs targeting Chagas Disease, and also make it possible to model the active site characteristics of the highly homologous Leishmania CYP51. This work provides a foundation for rational synthesis of new therapeutic agents targeting the three kinetoplastid parasites

Scanning Chimeragenesis: The Approach Used to Change Monoxygenase Cytochrome P450 BM3 into ω-Hydroxylase CYP4C7

It is believed that the specificity of cytochrome P450 is determined by a specific set of protein fragments that form the Substrate Recognition Site (SRS-1) and are responsible for a particular orientation of the bound substrate relative to the activated oxygen atom. Cytochrome P450 BM3 (CYP102A1) from Bacillus megaterium, is known for its high catalytic activity. Wild type BM3 catalyzes the oxidation of medium and long chain fatty acids (C12-18), and of farnesol, but the two form different metabolites, forms 9-hydroxyfarnesol and 10,11- and 2,3-epoxyfarnesol in a ratio of 3:3:2 and 12-hydroxyfarnesol, respectively. CYP102A1 and CYP4C7 share a common substrate, farnesol. Therefore, CYP4C7 has become the target for homologous replacements in CYP102A1. CYP4C7 from Diploptera Punctata (Pacific Beetle Cockroach) only catalyzes farnesol to produce 12-hydroxyfarnesol as its primary metabolite, with no activity towards fatty acids. By using the technique of scanning chimeragenesis, in this work three generations of chimeras have created twenty chimeric proteins. By starting with CYP102A1 as the experimental model and employing sequential rounds of selective mutagenesis, the third generation mutant C(78-82,F87L,328-330) was produced, which catalyzed the 12- and 15-hydroxylation of farnesol as its major products in a 3:1 ratio with a hundred-fold increase in catalytic activity compared to the wild type CYP4C7, and a two-fold increase over CYP102A1. Based on the activity assay results for the chimeric proteins with substrates geranyl-geraniol, 10,11-epoxymethylfarnesoate (JH III), methylfarnesoate, farnesol, geraniol, 3,7-dimethyl-1-octanol, and lauric and palmitic acids, most chimeric proteins showed a change in substrate selectivity and/or regiospecificity. Scanning chimeragenesis can be used as a tool to not only study the relationship between the protein fragments that form the substrate binding site, but also to help elucidate the roles of substrate selectivity and regiospecificity among any two cytochromes P450. Furthermore, this investigation has resulted in the production of highly efficient chimeric enzymes that have previously evaded other methods of sequence modification by mutagenesis or directed evolution and chemical synthesis