P4T-DOTA - a lanthanide chelating tag combining a sterically highly overcrowded backbone with a reductively stable linker

Herein we report a DOTA-based lanthanide chelating tag (LCT) with rigidified backbone and a reduction-stable linker. The newly developed tag induces strong pseudocontact shifts suitable for paramagnetic protein nuclear magnetic resonance spectroscopy and the obtained anisotropic susceptibility parameters are in the range of the best performing LCTs

Localization of ligands within human carbonic anhydrase II using F-19 pseudocontact shift analysis

Unraveling the native structure of protein-ligand complexes in solution enables rational drug design. We report here the use of 19F pseudocontact shift (PCS) NMR as a method to determine fluorine positions of high affinity ligands bound within the drug target human carbonic anhydrase II with high accuracy. Three different ligands were localized within the protein by analysis of the obtained PCS from simple onedimensional 19F spectra with an accuracy of up to 0.8 degrees A. In order to validate the PCS, four to five independent magnetic susceptibility tensors induced by lanthanide chelating tags bound site-specifically to single cysteine mutants were refined. Least-squares minimization and a Monte-Carlo approach allowed the assessment of experimental errors on the intersection of the corresponding four to five PCS isosurfaces. By defining an angle score that reflects the relative isosurface orientation for different tensor combinations, it was established that the ligand can be localized accurately using only three tensors, if the isosurfaces are close to orthogonal. For two out of three ligands, the determined position closely matched the X-ray coordinates. Our results for the third ligand suggest, in accordance with previously reported ab initio calculations, a rotated position for the difluorophenyl substituent, enabling a favorable interaction with Phe-131. The lanthanide-fluorine distance varied between 22 and 38 degrees A and induced 19F PCS ranged from 0.078 to 0.409 ppm, averaging to 0.213 ppm. Accordingly, even longer metal-fluorine distances will lead to meaningful PCS, rendering the investigation of protein-ligand complexes significantly larger than 30 kDa feasible

Near fatal posterior reversible encephalopathy syndrome complicating chronic liver failure and treated by induced hypothermia and dialysis: a case report

<p>Abstract</p> <p>Introduction</p> <p>Posterior reversible encephalopathy syndrome is a clinico-neuroradiological entity characterized by headache, vomiting, altered mental status, blurred vision and seizures with neuroimaging studies demonstrating white-gray matter edema involving predominantly the posterior region of the brain.</p> <p>Case presentation</p> <p>We report a 47-year-old Caucasian man with liver cirrhosis who developed posterior reversible encephalopathy syndrome following an upper gastrointestinal hemorrhage and who was managed with induced hypothermia for control of intracranial hypertension and continuous veno-venous hemodiafiltration for severe hyperammonemia.</p> <p>Conclusion</p> <p>We believe this is the first documented case report of posterior reversible encephalopathy syndrome associated with cirrhosis as well as the first report of the use of induced hypothermia and continuous veno-venous hemodiafiltration in this setting.</p

A Common Ca2+-Driven Interdomain Module Governs Eukaryotic NCX Regulation

Na+/Ca2+ exchanger (NCX) proteins mediate Ca2+-fluxes across the cell membrane to maintain Ca2+ homeostasis in many cell types. Eukaryotic NCX contains Ca2+-binding regulatory domains, CBD1 and CBD2. Ca2+ binding to a primary sensor (Ca3-Ca4 sites) on CBD1 activates mammalian NCXs, whereas CALX, a Drosophila NCX ortholog, displays an inhibitory response to regulatory Ca2+. To further elucidate the underlying regulatory mechanisms, we determined the 2.7 Å crystal structure of mammalian CBD12-E454K, a two-domain construct that retains wild-type properties. In conjunction with stopped-flow kinetics and SAXS (small-angle X-ray scattering) analyses of CBD12 mutants, we show that Ca2+ binding to Ca3-Ca4 sites tethers the domains via a network of interdomain salt-bridges. This Ca2+-driven interdomain switch controls slow dissociation of “occluded” Ca2+ from the primary sensor and thus dictates Ca2+ sensing dynamics. In the Ca2+-bound conformation, the interdomain angle of CBD12 is very similar in NCX and CALX, meaning that the interdomain distances cannot account for regulatory diversity in NCX and CALX. Since the two-domain interface is nearly identical among eukaryotic NCXs, including CALX, we suggest that the Ca2+-driven interdomain switch described here represents a general mechanism for initial conduction of regulatory signals in NCX variants

Aldol reactions in water using a beta-cyclodextrin-binding proline derivative

The aldol reaction of various arom. aldehydes with cyclohexanone catalyzed by the inclusion complex of a proline deriv. and beta-cyclodextrin in water is described.  A series of hydroxyketones was obtained using this method in good yields with anti/syn ratio of up to 99:1 and ee values well above 90%

Assembly of [2]Rotaxanes in Water

Two [2]rotaxanes have been assembled in water from modular subunits through Cu-I-catalyzed azide-alkyne click chemistry. For this purpose, 2,6-disubstituted naphthalene axles with solubilizing oligo(ethylene glycol) (OEG) chains (n = 1-5) and propargyl terminal groups were synthesized and examined for their propensity to form inclusion complexes with a dicationic Diederich-type cyclophane host. The dependence of pseudorotaxane formation on the linkers between the naphthalene core and OEG chains, and in the case of ester linkers on different spacer lengths, was analyzed by titration experiments. In addition, the inclusion complexes of two [2]rotaxanes were trapped by using a water-soluble azide-functionalized stopper. Repetitive chromatography finally enabled the isolation of both mechanically interlocked [2]rotaxanes

Donor-Acceptor Molecular Triangles

The synthesis and Pt electr nic properties of five donoracceptor molecules, featuring an electron-acceptor unit made of six fused benzenoid rings that resembles an equilateral triangle, are described. These molecular 'triangles' were synthesized in eight steps from simple building blocks such that the electron-donor substituents could be installed in the last step by means of the Suzuki cross-coupling reaction. All molecules absorb and emit visible light in the region of around 450-650 and 550-850 nm, respectively, exhibit solvatochromism, and possess up to four redox states

An Artificial Metalloenzyme Based on a Copper Heteroscorpionate Enables sp³ C-H Functionalization via Intramolecular Carbene Insertion

The selective functionalization of sp³ C–H bonds is a versatile tool for the diversification of organic compounds. Combining attractive features of homogeneous and enzymatic catalysts, artificial metalloenzymes offer an ideal means to selectively modify these inert motifs. Herein, we report on a copper(I) heteroscorpionate complex embedded within streptavidin that catalyzes the intramolecular insertion of a carbene into sp³ C–H bonds. Target residues for genetic optimization of the artificial metalloenzyme were identified by quantum mechanics/molecular mechanics simulations. Double-saturation mutagenesis yielded detailed insight on the contribution of individual amino acids on the activity and the selectivity of the artificial metalloenzyme. Mutagenesis at a third position afforded a set of artificial metalloenzymes that catalyze the enantio- and regioselective formation of β- and γ-lactams with high turnovers and promising enantioselectivities

Atropisomerization of di-para-substituted propyl-bridged biphenyl cyclophanes

The influence of electron donors and electron acceptors of variable strength in the 4 and 4' position of 2 and 2' propyl-bridged axial chiral biphenyl cyclophanes on their atropisomerization process was studied. Estimated free energies [capital Delta]G[double dagger](T) of the rotation around the central biphenyl bond which were obtained from 1H-NMR coalescence measurements were correlated to the Hammett parameters [sigma]p as a measure for electron donor and acceptor strength. It is demonstrated that the resulting nice linear correlation is mainly based on the influence of the different substituents on the [small pi]-system of the biphenyl cyclophanes. By lineshape analysis the rate constants were calculated and by the use of the Eyring equation the enthalpic and entropic contributions were evaluated. Density functional theory calculations show a planar transition state of the isomerization process and the calculated energy barriers based on this reaction mechanism are in good agreement with the experimentally obtained free energies