Enzyme structure with two catalytic sites for double-sieve selection of substrate

High-fidelity transfers of genetic information in the central dogma can be achieved by a reaction called editing. The crystal structure of an enzyme with editing activity in translation is presented here at 2.5 angstroms resolution. The enzyme, isoleucyl-transfer RNA synthetase, activates not only the cognate substrate L-isoleucine but also the minimally distinct L-valine in the first, aminoacylation step. Then, in a second, "editing" step, the synthetase itself rapidly hydrolyzes only the valylated products. For this two-step substrate selection, a "double-sieve" mechanism has already been proposed. The present crystal structures of the synthetase in complexes with L-isoleucine and L-valine demonstrate that the first sieve is on the aminoacylation domain containing the Rossmann fold, whereas the second, editing sieve exists on a globular beta-barrel domain that protrudes from the aminoacylation domain.     

Acute effect of inorganic iodide after 131I therapy for hyperthyroidism

Patients treated with inorganic iodide weeks to years following 131I therapy for hyperthyroidism do not adapt to its antithyroid effect. To determine whether such adaptation occurs soon after 131I therapy, serum thyroxine (T4) and triiodothyronine (T3) concentrations were measured daily for 9-14 days following 131I therapy in seventeen hyperthyroid patients. Nine patients received 150 mg KI daily starting 48 h after 131I administration; eight received only 131I. Serum T4 and T3 concentrations did not change significantly in the patients who received only 131I. In the patients who received 131I and KI, serum T4 and T3 concentrations fell promptly, reaching nadir values 2-10 days after initiation of iodide, and then increased despite continuation of KI therapy. The mean maximal fall in serum T4 was 34% and in serum T3 42%. These results show that "escape" from the acute anti-thyroid effect of iodide occurs when it is given immediately after 131I therapy, thus limiting the utility of iodide as a therapeutic agent at this time.     

Influence of Pasteurella multocida and Pasteurella-multocida endotoxin on the blood-coagulation-analytic parameter after experimental administration in calves

Experimental administration to calves of Pasteurella multocida or the application of an endotoxin preparation of the strain produced continuous decline of thrombocytes, disorders in thrombocytic functions, and the development of hypofibrinogenaemia. The changes recorded as well as the clinical symptoms and pathologico-anatomic findings are interpreted as endotoxin shock.     

The depolarization near-field scanning optical microscope: comparison of experiment and theory

The depolarization near-field scanning optical microscope allows for sub-wavelength optical resolution with uncoated optical fibre tips. We show by a simple thought experiment, by numerical solution of the Maxwell equations for a realistic geometry, and by direct experiments, that this novel apparatus images gradients of the dielectric function of a sample in the direction of the incident electric field vector. The near-field images obtained from experiment and theory agree well.     

Study on the Microstructure of Internally Oxidized Ag–Sn–In Alloys

The microstructures of five internally oxidized Ag–Sn–In materials were investigated using ion polishing, field emission scanning electron microscopy and electron backscatter diffraction. The ion polished sections showed a subtle material contrast in the oxide particles that could be attributed to different oxide phases generated during internal oxidation. The phases could be identified as tetragonal SnO₂ that surrounds the cubic In₂O₃ core of the combined oxide particles. It is shown that In₂O₃ exhibits an orientation relationship to the Ag matrix and for SnO₂ and Ag another orientation relationship is likely. Interrupted internal oxidation experiments were applied to identify the growth mechanism of the oxide particles. A consistent view on the role of In during the internal oxidation of Ag–Sn–In alloys as heterogeneous nucleation agent of SnO₂ is presented.     

SCALING IN SITU BIOREMEDIATION PROBLEMS BY APPLICATION OF MULTIPHASE, MULTICOMPONENT TRANSPORT THEORY

A methodology for scaling in situ bioremediation problems is presented. This methodology is based on multiphase, muiticomponent transport theory and employs inspectional analysis and numerical sensitivity studies. A general mathematical model that describes subsurface aerobic biotransformation of organic chemical species in a multiphase setting is first presented. This general model is applied to the specific case of microbial enhanced vapor-vacuum extraction (MEVVE) in a one-dimensional zone of immobile liquids. The resulting simplified MEVVE model considers rate-dependent interphase mass transfer, a flowing gaseous phase, a single hydrocarbon pseudo-component, and either oxygen or hydrocarbon limited microbial activity. By inspectional analysis a set of dimensionless groups are derived that represent the various model parameters. A scries of numerical sensitivity studies are presented that examine the impact of selected dimensionless groups on overall system biotransformation rates. This analysis demonstrates that overall biotranformation rates can be significantly limited not only by insufficient transport of oxygen in the gaseous phase, but also by interfacial mass transfer resistance between nonaqueous phase liquid globules and adjacent fluids. Finally, an examination of the selected dimensionless groups reveals the parameter requirements for properly scaled MEVVE tests. These results indicate the need for further investigation of the importantance of fluid distributions in the pore space and their impact on the design of laboratory and field tests.     

Reconstruction of quaternary structures of class II tRNA synthetases by rational mutagenensis of a conserved domain

Class II tRNA synthetases have long been known to have quaternary structures of alpha, alpha2, alpha2beta2, and alpha4, depending on the amino acid specificity and the organism from which the synthetase was isolated. Even the quaternary structures of enzymes for the same amino acid show variations in evolution. The basis for these variations has not been understood. We report here that sequence manipulations of a structural motif (motif 1) characteristic of all class II tRNA synthetases can generate most of the evolutionary diversity of quaternary forms of class II synthetases. Thus, the principles elucidated here for quaternary structure assembly may be general.     

Nanofur for Biomimetic Applications

Many plants and insects possess multi‐functional surfaces covered by dense nanohair. Such a nanofur is of high interest for various biomimetic applications like self‐healing, air retention, and oil/water separation. Here, we introduce a highly scalable and competitive molding technique for the fabrication of biomimetic nanofur. With this method, we pull nanofur out of flat polycarbonate and tune its wettability from hydrophilic to superhydrophobic. By mechanically structuring these samples we create various devices suitable for microfluidics. The nanofur can be also used for the fabrication of self‐healing surfaces inspired by pitcher plants as well as for air‐retaining surfaces mimicking the water fern Salvinia minima. Finally, we utilize the nanofur for oil/water separation and the cleaning of oil spills.     

Maintaining genetic code through adaptations of tRNA synthetases to taxonomic domains

The universal genetic code is determined by the aminoacylation of tRNAs. In spite of the universality of the code, there are barriers to aminoacylation across taxonomic domains. These barriers are thought to correlate with the co-segregation of sequences of synthetases and tRNAs into distinct taxonomic domains. By contrast, we show here examples of eukaryote-like synthetases that are found in certain prokaryotes. The associated tRNAs have retained their prokaryote-like character in each instance. Thus, co-segregation of domain-specific synthetases and tRNAs does not always occur. Instead, synthetases make adaptations of tRNA-protein contacts to cross taxonomic domains.     

Functional analysis of peptide motif for RNA microhelix binding suggests new family of RNA-binding domains

RNA microhelices that recreate the acceptor stems of transfer RNAs are charged with specific amino acids. Here we identify a two-helix pair in alanyl-tRNA synthetase that is required for RNA microhelix binding. A single point mutation at an absolutely conserved residue in this motif selectively disrupts RNA binding without perturbation of the catalytic site. These results, and findings of similar motifs in the proximity of the active sites of other tRNA synthetases, suggest that two-helix pairs are widespread and provide a structural framework important for contacts with bound RNA substrates.