No Correlation Between Rates of Suicidal Ideation and Completed Suicides in Europe: Analysis of 49,008 Participants (55+ Years) Based on the Survey of Health, Ageing and Retirement in Europe (SHARE)

Background:

Little is known about country-specific variations in suicidal ideation (SID) by sex and how they correspond with completed suicide rate. Therefore, the aim of the present study was to assess variations in SID prevalence rates by sex and its correlation to completed suicide rates across European countries.

Method:

SHARE is a cross-national European survey of individuals over the age of 50 and their spouse of any age. The present study relied on wave 4 conducted in 2010–2012 including 49,008 participants aged 55 to 104 years from 16 countries. SID was evaluated using a single item from the Euro-D. Data on completed suicide rates were taken from the WHO mortality database.

Results:

Of the study population (n = 49,008, 44.3% men, mean age 68.2 ± 9.1 years), a total of 4139 (8.5%, 95% CI 8.2–8.7) reported suicidal ideation within the last month. The women:men ratio in SID prevalence ranged from 1.30 in Estonia to 2.25 in Spain and Portugal. Regarding country-specific variation, the SID prevalence patterns of both men and women did not correspond to the completed suicide rates for males and females aged 55+ reported by the WHO (2013). Correlations were rather moderate in men (r = 0.45) and especially weak in women (r = 0.16).

Conclusion:

The study showed remarkable differences in SID prevalence by sex. The most exciting finding was that SID rates did not correspond with completed suicide rates in each country under investigation. However, the strength of these patterns substantially differs across countries. This unexpected finding need to be further evaluated.

Planctopirus ephydatiae, a novel Planctomycete isolated from a freshwater sponge

The microbiome of freshwater sponges is rarely studied, and not a single novel bacterial species has been isolated and subsequently characterized from a freshwater sponge to date. A previous study showed that 14.4% of the microbiome from Ephydatia fluviatilis belong to the phylum Planctomycetes. Therefore, we sampled an Ephydatia sponge from a freshwater lake and employed enrichment techniques targeting bacteria from the phylum Planctomycetes. The obtained strain spb1^T was subject to genomic and phenomic characterization and found to represent a novel planctomycetal species proposed as Planctopirus ephydatiae sp. nov. (DSM 106606 = CECT 9866). In the process of differentiating spb1^T from its next relative Planctopirus limnophila DSM 3776^T, we identified and characterized the first phage - Planctopirus phage vB_PlimS_J1 - infecting planctomycetes that was only mentioned anecdotally before. Interestingly, classical chemotaxonomic methods would have failed to distinguish Planctopirus ephydatiae strain spb1^T from Planctopirus limnophila DSM 3776^T. Our findings demonstrate and underpin the need for whole genome-based taxonomy to detect and differentiate planctomycetal species.

[Considerations and recommondations for species-appropriate and welfare friendly keeping of ratitae in Germany]

Ostrich farming and keeping in Germany is of increasing interest. Ostrich farming includes keeping the animals as agricultural livestock (production of meat, leather, eggs), for display, hobby farming and keeping in zoological collections. Based on scientific research there is a steady increase in knowledge of keeping ratites according to sophisticated standards in terms of animal welfare legislation. Legislation and recommondations for keeping of ratitae are described.

Detailed analysis of biased histamine H₄ receptor signalling by JNJ 7777120 analogues

BACKGROUND AND PURPOSE

The histamine H₄ receptor, originally thought to signal merely through Gαi proteins, has recently been shown to also recruit and signal via β-arrestin2. Following the discovery that the reference antagonist indolecarboxamide JNJ 7777120 appears to be a partial agonist in β-arrestin2 recruitment, we have identified additional biased hH₄R ligands that preferentially couple to Gαi or β-arrestin2 proteins. In this study, we explored ligand and receptor regions that are important for biased hH₄R signalling.

EXPERIMENTAL APPROACH

We evaluated a series of 48 indolecarboxamides with subtle structural differences for their ability to induce hH₄R-mediated Gαi protein signalling or β-arrestin2 recruitment. Subsequently, a Fingerprints for Ligands and Proteins three-dimensional quantitative structure-activity relationship analysis correlated intrinsic activity values with structural ligand requirements. Moreover, a hH₄R homology model was used to identify receptor regions important for biased hH₄R signalling.

KEY RESULTS

One indolecarboxamide (75) with a nitro substituent on position R7 of the aromatic ring displayed an equal preference for the Gαi and β-arrestin2 pathway and was classified as unbiased hH₄R ligand. The other 47 indolecarboxamides were β-arrestin2-biased agonists. Intrinsic activities of the unbiased as well as β-arrestin2-biased indolecarboxamides to induce β-arrestin2 recruitment could be correlated with different ligand features and hH₄R regions.

CONCLUSION AND IMPLICATIONS

Small structural modifications resulted in diverse intrinsic activities for unbiased (75) and β-arrestin2-biased indolecarboxamides. Analysis of ligand and receptor features revealed efficacy hotspots responsible for biased-β-arrestin2 recruitment. This knowledge is useful for the design of hH₄R ligands with biased intrinsic activities and aids our understanding of the mechanism of H₄R activation.

Design and pharmacological characterization of VUF14480, a covalent partial agonist that interacts with cysteine 98(3.36) of the human histamine H₄ receptor

BACKGROUND AND PURPOSE

The recently proposed binding mode of 2-aminopyrimidines to the human (h) histamine H₄ receptor suggests that the 2-amino group of these ligands interacts with glutamic acid residue E182(5.46) in the transmembrane (TM) helix 5 of this receptor. Interestingly, substituents at the 2-position of this pyrimidine are also in close proximity to the cysteine residue C98(3.36) in TM3. We hypothesized that an ethenyl group at this position will form a covalent bond with C98(3.36) by functioning as a Michael acceptor. A covalent pyrimidine analogue will not only prove this proposed binding mode, but will also provide a valuable tool for H4 receptor research.

EXPERIMENTAL APPROACH

We designed and synthesized VUF14480, and pharmacologically characterized this compound in hH4 receptor radioligand binding, G protein activation and β-arrestin2 recruitment experiments. The ability of VUF14480 to act as a covalent binder was assessed both chemically and pharmacologically.

KEY RESULTS

VUF14480 was shown to be a partial agonist of hH4 receptor-mediated G protein signalling and β-arrestin2 recruitment. VUF14480 bound covalently to the hH₄ receptor with submicromolar affinity. Serine substitution of C98(3.36) prevented this covalent interaction.

CONCLUSION AND IMPLICATIONS

VUF14480 is thought to bind covalently to the hH₄ receptor-C98(3.36) residue and partially induce hH₄ receptor-mediated G protein activation and β-arrestin2 recruitment. Moreover, these observations confirm our previously proposed binding mode of 2-aminopyrimidines. VUF14480 will be a useful tool to stabilize the receptor into an active confirmation and further investigate the structure of the active hH₄ receptor.

Stratification of patients with colorectal cancer of UICC stage II using prognostic mutations signatures obtained by deep amplicon sequencing of cancer genes

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Background: Assignment of patients (pts) with UICC-stage II colorectal cancer (CRC) to adjuvant therapy remains controversial. The clinical utility of histo-pathological parameters (pT4, L+, V+) as well as tumor RNA expression signatures like Oncotype Dx Colon Cancer Assay, ColoPrint, or Predictor C is low given their positive predictive value (PPV) of 0.13, 0.22, 0.19, and 0.33, respectively, when adjusted to an incidence of 10% for occurrence of metastatic disease (mets) within 3 years after diagnosis. Methods: We applied deep amplicon sequencing of 48 well-known cancer genes to DNA samples of primary tumors from 173 pts with UICC-stage II CRC using the Illumina MiSeq technology. Patients were selected from a prospective, multicenter clinical diagnostic study named MSKK. More than 6,500 patients with CRC have been recruited into this study conducted by 39 hospitals in Germany. 79 of the 173 pts had progression of disease events within 3 years after R0 resection including 40 pts with mets, 12 pts with local recurrences, and 27 pts with secondary malignancies. 94 pts remained progression-free. Results: Deep sequencing revealed a total of 2,221 sequence variations (SV) including missense, stop, InDel, noncoding, nonsense SV. 401 SV were in COSMIC, 750 SV in normal tissue. The remaining 1471 SV served as basis for development of SV-signatures (SVS) for prediction of progression events in a classical double-nested bootstrap approach in order to generate second order unbiased estimates of performance of SVS, namely sensitivity(S+), specificity (S-), PPV, and negative predictive value (NPV). The best SVS for prediction of metastases contained SV in less than 15 genes and has a S+ of 0.41, S- of 0.93, PPV of 0.40, and NPV of 0.93 (incidence of metastasis: 10%). The best SVS for prediction any progression event has a S+ of 0.33, S- of 0.93, PPV of 0.54, and NPV of 0.84 (incidence for any progression = 20.5%). Conclusions: This deep sequencing based prognostic tissue test with a PPV of 40% and a NPV of 93% represents a milestone over prognostic tests based on RNA expression. The increased PPV leads to more patients being treated correctly with adjuvant therapy.

[Successful treatment of secondary aortoesophageal fistula after thoracic endovascular aortic repair]

HISTORY AND CLINICAL SYMPTOMS: A 58-year-old man was admitted to our hospital with acute chest pain and subfebrile temperatures. Two years ago, endovascular aortic stent-graft placement had been performed for acute type B aortic dissection complicated by malperfusion syndrome.

DIAGNOSTIC ASSESSMENT

CT angiography showed a discrete soft-tissue attenuation mass between the aorta and esophagus. The patient developed progressive swallow disorder and esophago-gastro-duodenoscopy demonstrated deep esophageal ulcerations at the level of the implanted aortic stent-graft. Intravenous treatment with broad spectrum antibiotics was started. The FDG-PET/CT scan showed increased FDG uptake and air entrapment in the affected region establishing the diagnosis of aortoesophageal fistula formation.

THERAPY AND OUTCOME

Given the generally poor condition of the patient and the high risk of any aggressive surgical intervention, a new limited surgical approach was chosen consisting of open transthoracic esophageal resection, blind closure of the stomach and cervical esophagostomy. A percutaneous endoscopic gastrostomy tube was placed. After three months, esophageal continuity was restored by retrosternal colon interposition. The presented therapeutic management resulted in a full recovery of the patient.

CONCLUSION

Aortoesophageal fistula is a rare complication of thoracic aortic stent-graft placement. Patient may present with unspecific symptoms such as fever and rised inflammatory markers, but may also present with massive upper gastrointestinal bleeding. The herein presented limited therapy with esophageal resection represents a promising to the otherwise difficult therapy of aortoesophageal fistula.

Satellite radar interferometry for monitoring ice sheet motion: application to an antarctic ice stream

Satellite radar interferometry (SRI) provides a sensitive means of monitoring the flow velocities and grounding-line positions of ice streams, which are indicators of response of the ice sheets to climatic change or internal instability. The detection limit is about 1.5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction. The grounding line, detected by tidal motions where the ice goes afloat, can be mapped at a resolution of approximately 0.5 kilometer. The SRI velocities and grounding line of the Rutford Ice Stream, Antarctica, agree fairly well with earlier ground-based data. The combined use of SRI and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior.

Stoichiometric model of the photosynthetic unit of Ectothiorhodospira halochloris

A stoichiometric model of the photosynthetic unit of Ectothiorhodospira halochloris has been obtained by means of scanning transmission electron microscope mass determination and mass mapping in conjunction with polyacrylamide gel electrophoresis. One reaction center, consisting of four single polypeptides, including one cytochrome, is surrounded by six identical light-harvesting complexes, each containing three polypeptides with 2:2:2 stoichiometry. This stoichiometric model was incorporated into the three-dimensional structure of the photosynthetic unit as derived from surface relief reconstructions of the two surfaces of shadowed membranes. The reaction center protrudes substantially from both membrane surfaces and has the cytochrome attached to the periplasmic face in a noncentrosymmetric fashion. The reaction center may assume various orientations within the photosynthetic complexes.

Comparative study of the intestinal mucus barrier in normal and inflamed colon

AIM

To study the role of mucus in the spatial separation of intestinal bacteria from mucosa.

PATIENTS AND METHODS

Mucus barrier characteristics were evaluated using histological material obtained by biopsy from purged colon, colon prepared with enema and material from untreated appendices fixed with non-aqueous Carnoy solution. Bacteria were evaluated using fluorescence in situ hybridization, with bacterial 16S RNA probes and related to the periodic acid Schiff alcian blue stain. Biopsies from controls (n = 20), patients with self-limiting colitis (SLC; n = 20), ulcerative colitis (n = 20) and 60 randomly selected appendices were investigated.

RESULTS

The mucosal surface beneath the mucus layer was free of bacteria in > or =80% of the normal appendices and biopsies from controls. The thickness of the mucus layer and its spread decreased with increasing severity of the inflammation; the epithelial surface showed bacterial adherence, epithelial tissue defects and deep mucosal infiltration with bacteria and leucocytes. Bacteria and leucocytes were found within mucus in all biopsy specimens from patients with ulcerative colitis, SLC, and acute appendicitis. The concentration of bacteria within mucus was inversely correlated to the numbers of leucocytes.

CONCLUSIONS

The large bowel mucus layer effectively prevents contact between the highly concentrated luminal bacteria and the epithelial cells in all parts of the normal colon. Colonic inflammation is always accompanied by breaks in the mucus barrier. Although the inflammatory response gradually reduces the number of bacteria in mucus and faeces, the inflammation itself is not capable of preventing bacterial migration, adherence to and invasion of the mucosa.

Nano-structured support materials, their characterisation and serum protein profiling through MALDI/TOF-MS

In the bioanalytical era, novel nano-materials for the selective extraction, pre-concentration and purification of biomolecules prior to analysis are vital. Their application as affinity binding in this regard is needed to be authentic. We report here the comparative application of derivatised materials and surfaces on the basis of nano-crystalline diamond, carbon nanotubes and fullerenes for the analysis of marker peptides and proteins by material enhanced laser desorption ionisation mass spectrometry MELDI-MS. In this particular work, the emphasis is placed on the derivatization, termed as immobilised metal affinity chromatography (IMAC), with three different support materials, to show the effectiveness of MELDI technique. For the physicochemical characterisation of the phases, near infrared reflectance spectroscopy (NIRS) is used, which is a well-established method within the analytical chemistry, covering a wide range of applications. NIRS enables differentiation between silica materials and different fullerenes derivatives, in a 3-dimensional factor-plot, depending on their derivatizations and physical characteristics. The method offers a physicochemical quantitative description in the nano-scale level of particle size, specific surface area, pore diameter, pore porosity, pore volume and total porosity with high linearity and improved precision. The measurement takes only a few seconds while high sample throughput is guaranteed.

Switch of flow direction in an Antarctic ice stream

Fast-flowing ice streams transport ice from the interior of West Antarctica to the ocean, and fluctuations in their activity control the mass balance of the ice sheet. The mass balance of the Ross Sea sector of the West Antarctic ice sheet is now positive--that is, it is growing--mainly because one of the ice streams (ice stream C) slowed down about 150 years ago. Here we present evidence from both surface measurements and remote sensing that demonstrates the highly dynamic nature of the Ross drainage system. We show that the flow in an area that once discharged into ice stream C has changed direction, now draining into the Whillans ice stream (formerly ice stream B). This switch in flow direction is a result of continuing thinning of the Whillans ice stream and recent thickening of ice stream C. Further abrupt reorganization of the activity and configuration of the ice streams over short timescales is to be expected in the future as the surface topography of the ice sheet responds to the combined effects of internal dynamics and long-term climate change. We suggest that caution is needed when using observations of short-term mass changes to draw conclusions about the large-scale mass balance of the ice sheet.

Application of carboxymethyl-beta-cyclodextrin as a chiral selector in capillary electrophoresis for enantiomer separation of selected neurotransmitters

The aim of this work was to optimize conditions for capillary electrophoresis separation of different neurotransmitters (serotonin, phenylalanine, dopamine, adrenaline, ephedrine, propranolol and DOPA) in a single run, including separation of existing enantiomers. As chiral selectors added to the borate background, electrolyte unsubstituted alpha-, beta- and -gamma-cyclodextrins (CDs), methyl-, dimethyl-, and trimethyl-substituted beta-CDs, and hydroxypropyl-substituted alpha-, beta- and gamma-CDs were examined. Also carboxymethyl-beta-CD and succinyl-beta-CD were used for this purpose. In addition to the kind and concentration of chiral selector, some other experimental factors also have been optimized, such as concentration of borate buffer, content of methanol, pH of electrolyte, method of sample introduction into the capillary and washing procedure between consecutive runs. The best results were obtained using 20 mM carboxymethyl-beta-CD in borate buffer of pH 7.5 as running electrolyte and hydrostatic injection. The obtained sensitivity of response (peak height) varied from 0.4 for adrenalines to 2.3 mAU mM(-1) for propranolols. The concentration detection limits (S/N=3) were in the range from 0.04 mM for propranolols to 0.2 mM for adrenalines. The resolution obtained in optimized conditions in a single run was from 0.75 for adrenalins and 1.0 for propranolols up to 2.0 for ephedrines. The developed method was employed for determination of these analytes in brain tissue extracts.

The fla gene cluster is involved in the biogenesis of flagella in Halobacterium salinarum

In this study, a flagella-related protein gene cluster is described for Halobacterium salinarum. The fla gene cluster is located upstream of the flagellin genes flgB1-3 and oriented in the opposite direction. It consists of nine open reading frames (ORFs): htpIX, a member of the halobacterial transducer protein gene family, and the genes flaD-K. The genes flaD, E, G, H, I and J share high homologies with genes from other Archaea. Interestingly, flaK shows similarities to bacterial genes involved in the regulation of flagellar synthesis. The ORFs of flaH, flaI and flaK contain sequences coding for nucleotide binding sites. Furthermore, flaI contains a motif called the bacterial type II secretion protein E signature, indicating a functional relation to members of the bacterial pili type IV-type II secretion protein superfamily. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that the genes flaE to flaK are transcribed into one polycistronic message. In frame deletion mutants of flaI were generated by gene replacement. The deletion strain lacks motility and belongs to the fla(-) mutant class, indicating that it is deficient in flagellar biogenesis. The overall amount of flagellin protein in Delta flaI cells is reduced, although transcription of the flagellin genes is unaffected. Therefore, the flaI gene product is involved in the biosynthesis, transport or assembly of flagella in H. salinarum.

Summary of the first round analyses of the Third International Workshop on Swine Leukocyte Differentiation Antigens

The reactivity of 155 monoclonal antibodies submitted to the Third International Workshop on Swine Leukocyte Differentiation Antigens, together with 41 internal standards, was analysed by flow cytometry on 29 different pig cell targets as well as two human cell targets as a means of establishing suitable panels of monoclonal antibodies for more detailed clustering analyses by the various subsections of the workshop. Results were collected either without further gating, with gating based on FS/SS characteristics or with gating based on the co-expression of a reference antibody in two-colour flow cytometry. The CD or SWC reactivity of the internal standards had been established in previous workshops. Data sets were subsequently analysed by statistical clustering using the Leucocyte Typing Database IV software. The resulting 18 cluster groups were allocated to the appropriate second round sections of the workshop, after reviewing the overall cellular reactivity of each cluster as well as the specificity of known standards which clustered in a group.

Overview of the Third International Workshop on Swine Leukocyte Differentiation Antigens

The aim of the Third International Workshop on Swine Leukocyte Differentiation Antigens (CD workshop), supported by the Veterinary Immunology Committee (VIC) of the International Union of Immunological Societies (IUIS), was to standardize the assignment of monoclonal antibodies (mAb) reactive with porcine leukocyte differentiation antigens and to define new antibody clusters, using nomenclature in accordance with human and ruminant CD nomenclature, as agreed at the summary meeting of the Second International Swine CD Workshop in Davis, 1995: only mAb with proven reactivity for the orthologous porcine gene product or cross-reactivity for the human gene products, were given the full CD nomenclature, all other allocations were prefixed with "w". As in previous workshops, the overall organization was entrusted to the chair and first author, with support by the chair of the previous workshop and second author. In addition to the existing 26 pig leukocyte CD/SWC determinants established in previous workshops, this workshop established/confirmed another 11 CDs for pig leukocytes, identified by a total of 21 mAb: CD11R1 (2 mAb), CD11R2 (1 mAb), CD11R3 (4 mAb), wCD40 (1 mAb), wCD46 (4 mAb), wCD47 (3 mAb), wCD49d (1 mAb), CD61 (1 mAb), wCD92 (1 mAb), wCD93 (1 mAb) and CD163 (2 mAb).

MspA provides the main hydrophilic pathway through the cell wall of Mycobacterium smegmatis

MspA is an extremely stable, oligomeric porin from Mycobacterium smegmatis that forms water-filled channels in vitro. Immunogold electron microscopy and an enzyme-linked immunosorbent assay demonstrated that MspA is localized in the cell wall. An mspA deletion mutant did not synthesize detectable amounts of mspA mRNA, as revealed by amplification using mspA-specific primers and reverse-transcribed RNA. Detergent extracts of the DeltamspA mutant exhibited a significantly lower porin activity in lipid bilayer experiments and contained about fourfold less porin than extracts of wild-type M. smegmatis. The chromosome of M. smegmatis encodes three proteins very similar to MspA. Sequence analysis of the purified porin revealed that mspB or mspC or both genes are expressed in the DeltamspA mutant. The properties of this porin, such as single channel conductance, extreme stability against denaturation, molecular mass and composition of 20 kDa subunits, are identical to those of MspA. Deletion of mspA reduced the cell wall permeability towards cephaloridine and glucose nine- and fourfold respectively. These results show that MspA is the main general diffusion pathway for hydrophilic molecules in M. smegmatis and was only partially replaced by fewer porins in the cell wall of the DeltamspA mutant [corrected] This is the first experimental evidence that porins are the major determinants of the exceptionally low permeability of mycobacteria to hydrophilic molecules.

Simultaneous determination of alkali, alkaline earth and transition metal ions by capillary electrophoresis with indirect UV detection

Determination of metal ions in aqueous samples using capillary electrophoresis can be accomplished with indirect UV detection. For optimal determination of alkali, alkaline earth, and transition metal ions, several electrolyte systems were studied. Detection at 214 nm was performed with a background electrolyte containing reagents with inherent absorbance in the UV range: imidazole, 4-methylbenzylamine and 4-aminopyridine. Glycolic acid and alpha-hydroxyisobutyric acid were used as complexing reagents. A mixture of 16 metal ions was successfully separated. The detection limits were between 92 ppb for Ca and 454 ppb for Cu with hydrostatic injection. All peaks were completely resolved and well separated. A separation efficiency of about 650,000 theoretical plates per meter was achieved for the Mg ion. The described methods can be used successfully in routine analysis of real samples. One of the methods was applied to an environmental water sample from the Georgian river Kasretula.

Characterization of synthetic polyelectrolytes by capillary electrophoresis

Capillary electrophoresis in entangled polymer solutions was applied to determine the molecular mass and polydispersity of polyelectrolytes. The separation selectivities of different polyethylene glycols as buffer additive can be correlated to their average molecular mass. A universal curve correlating the selectivity and the molecular mass could be obtained by using the instrinsic viscosity of the polyethylene glycol. The separation of poly(2-vinylpyridine) standards was compared to the separation of poly(4-vinylpyridine) standards. An indirect detection system was developed to characterize the cationic polyelectrolyte polydiallyldimethyl ammonium chloride. Various polymers with oppositely charged groups (polycarboxybetaines) were investigated with respect to structure dependence, pH dependence and molecular mass dependence of interand intramolecular association.

Crystal structure of Omp32, the anion-selective porin from Comamonas acidovorans, in complex with a periplasmic peptide at 2.1 A resolution

BACKGROUND

Porins provide diffusion channels for salts and small organic molecules in the outer membrane of bacteria. In OmpF from Escherichia coli and related porins, an electrostatic field across the channel and a potential, originating from a surplus of negative charges, create moderate cation selectivity. Here, we investigate the strongly anion-selective porin Omp32 from Comamonas acidovorans, which is closely homologous to the porins of pathogenic Bordetella and Neisseria species.

RESULTS

The crystal structure of Omp32 was determined to a resolution of 2.1 A using single isomorphous replacement with anomalous scattering (SIRAS). The porin consists of a 16-stranded beta barrel with eight external loops and seven periplasmic turns. Loops 3 and 8, together with a protrusion located within beta-strand 2, narrow the cross-section of the pore considerably. Arginine residues create a charge filter in the constriction zone and a positive surface potential at the external and periplasmic faces. One sulfate ion was bound to Arg38 in the channel constriction zone. A peptide of 5.8 kDa appeared bound to Omp32 in a 1:1 stoichiometry on the periplasmic side close to the symmetry axis of the trimer. Eight amino acids of this peptide could be identified, revealing specific interactions with beta-strand 1 of the porin.

CONCLUSIONS

The Omp32 structure explains the strong anion selectivity of this porin. Selectivity is conferred by a positive potential, which is not attenuated by negative charges inside the channel, and by an extremely narrow constriction zone. Moreover, Omp32 represents the anchor molecule for a peptide which is homologous to proteins that link the outer membrane to the cell wall peptidoglycan.

Expression, two-dimensional crystallization, and three-dimensional reconstruction of the beta8 outer membrane protein Omp21 from Comamonas acidovorans

The Omp21 protein from the proteobacterium Comamonas (Delftia) acidovorans belongs to the recently described beta8 family of outer membrane proteins, characterized by eight antiparallel beta-strands which form a beta-barrel. This family includes virulence proteins, OmpA and OmpX from Escherichia coli, and other related molecules. After we established an expression system, recombinant Omp21 was purified by Ni(2+) chelation affinity chromatography and refolded in situ while bound to resin. The native state of refolded protein was proven by FTIR spectroscopy and monitored with denaturing PAGE (heat modification). Both native and recombinant Omp21 were reconstituted in lipid membranes and crystallized two-dimensionally by controlled dialysis. Recombinant Omp21 crystallized as dimer and formed a p22(1)2(1) lattice with constants of a = 11.1 nm, b = 12.2 nm, gamma = 89.5 degrees. The 3-D structure of negatively stained, recombinant Omp21 was determined at a resolution of 1.8 nm by means of electron crystallography. Comparison with 3-D maps of OmpX and the transmembrane domain of OmpA revealed a high similarity between the mass distribution of exoplasmic loops of Omp21 and OmpA.