Cover Picture

The cover picture shows an array of several hundred synthetically produced variants of the 44 amino acids comprising the hyAP-WW protein domain. The array was produced by a stepwise SPOT synthesis on a cellulose membrane. At each synthesis site (spot) a WW domain is bound to the membrane through a C-terminal ester bond. The secondary structure of the WW domain is shown in green as a ribbon. The domains of the single spots differ only by a single amino acid. All the domains were tested simultaneously for their ability to bind to a peptide motif (red) common to many proteins. The binding was evident when visualized by chemoluminescence, with the Spots having various intensities. The systematic analysis undertaken here enabled molecular biology to be carried out that would have otherwise have required great effort, or not been done at all. This chemical technique also allows the construction of many non-genetically coded building blocks. Through the use of modern synthetic techniques for the coupling of peptides this method should also allow the synthesis of proteins. The combination of molecular biological and chemical methods opens up opportunities for the preparation of protein chips for diagnostics and drug discovery. More about this can be found in the article by Schneider-Mergener et al. on p. 897ff.     

Silver- and Coomassie-staining protocols: detection limits and compatibility with ESI MS

Staining protocols for PAGE have to be sensitive and should not impair further MS analysis of selected samples. In this study, the MS compatibility of different silver- and Coomassie-staining protocols with a nano-LC-MS/MS system was systematically elucidated. Altogether, 13 different silver-staining, 1 imidazole-staining and 2 Coomassie-staining protocols were used and compared to each other for their achieved sequence coverage and their detection sensitivity. Three proteins were used as model proteins (bovine serum albumin, rabbit L-lactate dehydrogenase, bovine milk beta-lactoglobulin) in decreasing concentration (12 pmol down to 30 fmol) and different staining protocols were applied. The conclusion of this study is that two silver-staining protocols (Blum, H. et al.,. Electrophoresis 1987, 8, 93-99 and Shevchenko, A. et al.,. Anal. Chem. 1996, 68, 850-858) combine good sequence coverage and good sensitivity and are recommended for nano-LC-MS/MS analysis.     

Extractability, stability, and allergenicity of egg white proteins in differently heat-processed foods

Hen's egg white protein is a major cause of food allergy, and a considerable number of countries have introduced labeling directions for processed food products. To control compliance with these regulations, analytical assays for the detection of egg in manufactured foods have been developed. In this study, we have tested the performance of 3 commercially available kits for quantitative egg analysis using 6 model heat-processed foods. The 3 assays worked well under standard conditions with soluble egg white proteins, but only the kit using a denaturing-reducing extraction buffer detected egg in complex heat-treated food matrixes. The differently extracted food samples were further used to evaluate the stability and allergenicity of the egg white allergens ovalbumin, ovomucoid, ovotransferrin, and lysozyme with polyclonal anti-egg antibodies and sera of 6 patients with egg allergy. It could be shown that differences in egg protein extractability have a significant impact on the interpretation of study results.     

Toward mechanical switching of surface-adsorbed [2]catenane by in situ copper complexation

Using scanning tunneling microscopy (STM), electrospray ionization mass spectrometry (ESI-MS), and X-ray photoelectron spectroscopy (XPS), we demonstrate that a free [2]catenane consisting of two interlocking 30-membered rings (cat-30) can be deposited on a Ag(111) surface by vacuum sublimation without decomposition. The deposited cat-30 molecules self-organize as ordered dimer chain structures at the surface, presumably via intermolecular pi-pi stacking. An in situ addition of Cu atoms to the surface-adsorbed catenanes induces a drastic change in the molecular organization, i.e., from the dimer chain structure to isolated species. The nitrogen core level spectra suggest that the cat-30 phenanthroline units coordinate with Cu, indicating that the free catenane has been transformed into a Cu-complexed [2]catenane. Since it is known that the two interlocked macrocyclic rings of the free ligand cat-30 completely rearrange, i.e., circumrotate, upon complexation to copper, our results reveal that when adsorbed on the silver surface, the two macrocyclic rings of the free [2]catenane can glide within one another so as to generate the corresponding copper complex by in situ Cu complexation.     

Speciation of uranyl complexes in ionic liquids by optical spectroscopy

Uranyl complexes dissolved in room-temperature ionic liquids have diagnostic absorption and emission spectra which reflect the molecular symmetry and geometry. In particular, the characteristic vibrational fine structure of the absorption spectra allows identification of the molecular symmetry of a uranyl complex. The concept of speciation of uranyl complexes is illustrated for the hydrated uranyl ion, the tetrachloro complex [UO2Cl4]2-, the trinitrato complex [UO2(NO3)3]-, the triacetato complex [UO2(CH3COO)3]-, and the crown ether complex [UO2(18-crown-6)]2+ in imidazolium and pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids. The competition between 18-crown-6 and small inorganic ligands for coordination to the uranyl ion was investigated. The crystal structures of the hydrolysis product [(UO2)2(mu2-OH)2(H2O)6] [UO2Br4](18-crown-6)4 and imidazolium salt [C6mim]2[UO2Br4] are described.     

Synthesis of the tricyclic core of vinigrol via an intramolecular Diels-Alder reaction

[reaction: see text] Herein, we present a successful synthesis of the tricyclic core of vinigrol (1). Our approach takes advantage of a highly regioselective intramolecular Diels-Alder reaction of the diene 11 to construct two rings of the tricyclic vinigrol skeleton 12.     

Efficient nucleophilic aromatic substitution between aryl nitrofluorides and alkynes

The nucleophilic aromatic substitution reaction between electron-deficient aryl fluorides and terminal alkynes is shown to be efficiently promoted by sodium bis(trimethylsilyl)amide as a base. Moderate to excellent yields of 2-ethynylnitrobenzene products can be obtained under mild conditions.     

Glutathione reductase-catalyzed cascade of redox reactions to bioactivate potent antimalarial 1,4-naphthoquinones--a new strategy to combat malarial parasites

Our work on targeting redox equilibria of malarial parasites propagating in red blood cells has led to the selection of six 1,4-naphthoquinones, which are active at nanomolar concentrations against the human pathogen Plasmodium falciparum in culture and against Plasmodium berghei in infected mice. With respect to safety, the compounds do not trigger hemolysis or other signs of toxicity in mice. Concerning the antimalarial mode of action, we propose that the lead benzyl naphthoquinones are initially oxidized at the benzylic chain to benzoyl naphthoquinones in a heme-catalyzed reaction within the digestive acidic vesicles of the parasite. The major putative benzoyl metabolites were then found to function as redox cyclers: (i) in their oxidized form, the benzoyl metabolites are reduced by NADPH in glutathione reductase-catalyzed reactions within the cytosols of infected red blood cells; (ii) in their reduced forms, these benzoyl metabolites can convert methemoglobin, the major nutrient of the parasite, to indigestible hemoglobin. Studies on a fluorinated suicide-substrate indicate as well that the glutathione reductase-catalyzed bioactivation of naphthoquinones is essential for the observed antimalarial activity. In conclusion, the antimalarial naphthoquinones are suggested to perturb the major redox equilibria of the targeted infected red blood cells, which might be removed by macrophages. This results in development arrest and death of the malaria parasite at the trophozoite stage.     

In vitro phase I metabolism of the depsipeptide enniatin B

The enniatins are a group of more than 20 cyclic depsipeptides from fungi with numerous biological effects. Enniatin B is commonly one of the principal analogues in species of the genus Fusarium, known to have ionophoric, antibiotic and insecticidal activity. In the present study, enniatin B was incubated with rat, dog and human liver microsomes. The compound was extensively metabolised, and 12 biotransformation products (M1–M12) were detected and their structures tentatively identified using a combination of mass spectrometric techniques and chemical derivatisation. Ion trap mass spectrometry, multiple-stage MS ⁿ fragmentation and high-resolution mass spectrometry were the instrumental backbone for structural determination, while acetylation, methylation and Jones oxidation were useful derivatisation techniques for the localisation of the site of biotransformation. Comparison of mass spectrometric data of the metabolism products with that of enniatin B suggested that M1–M5 are monohydroxylated species, while M8–M12 are the result of multiple oxidations (oxygenation and dehydrogenation). Metabolites M6 and M7 appeared to be enniatin B homologues and are the result of N-demethylation. Our findings show that oxidation and N-demethylation are the principal metabolic pathways in enniatin B phase I metabolism.