The role of residues outside the active site: structural basis for function of C191 mutants of Escherichia coli aspartate aminotransferase

In previous kinetic studies of Escherichia coli aspartate aminotransferase,it was determined that some substitutions of conserved cysteine191, which is located outside of the active site, altered thekinetic parameters of the enzyme (Gloss,L.M., Spencer,D.E. andKirsch,J.F., 1996, Protein Struct. Funct. Genet., 24, 195–208).The mutations resulted in an alkaline shift of 0.6–0.8pH units for the pK_a of the internal aldimine between the PLPcofactor and Lys258. The change in the pK_a affected the pH dependenceof the k_cat/K_m (aspartate) values for the mutant enzymes. Tohelp to understand these observations, crystal structures offive mutant forms of E.coli aspartate aminotransferase (themaleate complexes of C191S, C191F, C191Y and C191W, and C191Swithout maleate) were determined at about 2 Å resolutionin the presence of the pyridoxal phosphate cofactor. The overallthree-dimensional fold of each mutant enzyme is the same asthat of the wild-type protein, but there is a rotation of themutated side chain around its C     

An evaluation of the impact of SG1 disproportionation and the addition of styrene in NMP of methyl methacrylate

A kinetic modeling study is presented for batch nitroxide mediated polymerization (NMP) of methyl methacrylate (MMA; nitroxide: N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] (SG1)). Arrhenius parameters for SG1 disproportionation (A = 1.4 10⁷ L mol^?1 s^?1; E_a = 23 kJ mol^?1) are reported, based on homopolymerization data accounting for unavoidable temperature variations with increasing time, that is, nonisothermicity. For low targeted chain lengths (TCLs ≤ 300), this nonisothermicity is also relevant for NMP of MMA with a small amount of styrene. Parameter tuning to copolymerization data confirms a penultimate monomer unit effect for activation (s_a2 = k_a12/k_a22=6.7; 363 K; 1: MMA; 2: styrene). To obtain, for a broad TCL range (up to 800), a dispersity well below 1.3 an initial styrene mass fraction of ca. 10% is required. An interpretation of the comonomer incorporation is performed by calculating the fractions of activation‐growth‐deactivation cycles with a given amount of monomer units and the copolymer composition distribution. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2545–2559, 2018     

Defective Lysosomal Lipolysis Causes Prenatal Lipid Accumulation and Exacerbates Immediately after Birth

Cholesterol and fatty acids are essential lipids that are critical for membrane biosynthesis and fetal organ development. Cholesteryl esters (CE) are degraded by hormone-sensitive lipase (HSL) in the cytosol and by lysosomal acid lipase (LAL) in the lysosome. Impaired LAL or HSL activity causes rare pathologies in humans, with HSL deficiency presenting less severe clinical manifestations. The infantile form of LAL deficiency, a lysosomal lipid storage disorder, leads to premature death. However, the importance of defective lysosomal CE degradation and its consequences during early life are incompletely understood. We therefore investigated how defective CE catabolism affects fetus and infant maturation using Lal and Hsl knockout (-/-) mouse models. This study demonstrates that defective lysosomal but not neutral lipolysis alters placental and fetal cholesterol homeostasis and exhibits an initial disease pathology already in utero as Lal-/- fetuses accumulate hepatic lysosomal lipids. Immediately after birth, LAL deficiency exacerbates with massive hepatic lysosomal lipid accumulation, which continues to worsen into young adulthood. Our data highlight the crucial role of LAL during early development, with the first weeks after birth being critical for aggravating LAL deficiency.     

Synthese neuer N-Aroylisothiazol-2-imine und N-Aroylamino-isothiazoliumsalze durch Cyclisierung von thiocyanato-substituierten Hydrazonen

Synthesis of New N-Aroylisothiazole-2-imines and N-Aroylaminoisothiazolium Salts by Cyclisation of Thiocyanato-substituted Hydrazones The synthesis of new N-aroylisothiazole-2-imines ( 4g-n ) as well as the corresponding acceptor-substituted 2-amino-isothiazolium salts ( 6f-n ) by cyclocondensation of thiocyanatovinylaldehyde hydrazones ( 3 ) is reported. The structure of these N-imines was proved by spectroscopic methods. The alternative cyclization route to 1,2,3-thiadiazines ( 8 ) is not observed. The hydrazones ( 3a-e ) could not be cyclized to N-imines, only sulfides ( 5a-c ) were obtained. The reaction of 2-thiocyanatomethylen-cycloheptan-2-one ( 9 ) with benzhydrazides gave the same ring closure to the salts ( 10a,b ). The structure of the N-imine 11b has been confirmed unequivocally by X-ray structure analysis.     

Acylierung von Heterocyclen mit Kohlensäurederivaten. II. Endo- und exo-Carbamoylierung von 2-Amino-benzimidazol-Derivaten mit Isocyanaten. Mechanismus der Acylgruppenwanderung

Acylation of Heterocycles with Carbonic Acid Derivatives. II. Endo and Exo Carbamoylation of 2-Amino-benzimidazole Derivatives with Isocyanates. Mechanism of the Acyl Group Migration 2-Amino-benzimidazoles react with isocyanates with good yields to give 2-amino-1-carbamoyl-aminobenzimidazoles 1 at −30°C and the corresponding 2-carbamoyl isomeres 2 at room temperature, respectively. The isomerization mechanism was studied by crossover experiments and kinetic measurements and has been found to consist of inter- and monomolecular acyl transfer.     

Surface Design Options in Polymer- and Lipid-Based siRNA Nanoparticles Using Antibodies

The mechanism of RNA interference (RNAi) could represent a breakthrough in the therapy of all diseases that arise from a gene defect or require the inhibition of a specific gene expression. In particular, small interfering RNA (siRNA) offers an attractive opportunity to achieve a new milestone in the therapy of human diseases. The limitations of siRNA, such as poor stability, inefficient cell uptake, and undesired immune activation, as well as the inability to specifically reach the target tissue in the body, can be overcome by further developments in the field of nanoparticulate drug delivery. Therefore, types of surface modified siRNA nanoparticles are presented and illustrate how a more efficient and safer distribution of siRNA at the target site is possible by modifying the surface properties of nanoparticles with antibodies. However, the development of such efficient and safe delivery strategies is currently still a major challenge. In consideration of that, this review article aims to demonstrate the function and targeted delivery of siRNA nanoparticles, focusing on the surface modification via antibodies, various lipid- and polymer-components, and the therapeutic effects of these delivery systems.     

Cost-efficient modeling of distributed molar mass and topological variations in graft copolymer synthesis by upgrading the method of moments

Cost-efficient deterministic method of moments solvers, as widely used to calculate average characteristics of chemical processes driven by population variations (e.g., average chain lengths), can be a posteriori extended with approximated solutions delivering distributed properties (e.g., chain length distributions). However, these solutions are rarely verified, specifically for complex systems with many population members and strong coupling, as is the case for industrially relevant free-radical-induced grafting (FRIG) toward graft copolymer (GC) synthesis with monomer unit dependent reactions. FRIG, as studied in the present work with polybutadiene at low styrene conversions, is an important chemical process, for example, the production of compatibilizers and high-impact materials. Deterministic model validation is uniquely performed by benchmarking the low to medium molar mass (MM) results (29 topologies) in the log-molar mass distribution with detailed matrix-based kinetic Monte Carlo simulation output, inherently capable of mapping distributions. The GC product is identified to be a heterogeneous mixture in MM, chemical composition, and molecular topology at any styrene conversion. The molecular structural evolution during GC synthesis is further theoretically related to both one-dimensional size-exclusion chromatography (1D-SEC) and two-dimensional liquid chromatography (2D-LC) analysis. It is shown that conventional SEC—even in the absence of broadening—is insufficient for GC separation, mainly due to the unavoidable coelution of topologically different GC species. In any case, the parallel running of advanced modeling tools allows for detailed molecular interpretation.     

Human control of complex objects: towards more dexterous robots

Manipulation of objects with underactuated dynamics remains a challenge for robots. In contrast, humans excel at ‘tool use’ and more insight into human control strategies may inform robotic control architectures. We examined human control of objects that exhibit complex – underactuated, nonlinear, and potentially chaotic dynamics, such as transporting a cup of coffee. Simple control strategies appropriate for unconstrained movements, such as maximizing smoothness, fail as interaction forces have to be compensated or preempted. However, predictive control based on internal models appears daunting when the objects have nonlinear and unpredictable dynamics. We hypothesized that humans learn strategies that make these interactions predictable. Using a virtual environment subjects interacted with a virtual cup and rolling ball using a robotic visual and haptic interface. Two different metrics quantified predictability: stability or contraction, and mutual information between controller and object. In point-to-point displacements subjects exploited the contracting regions of the object dynamics to safely navigate perturbations. Control contraction metrics showed that subjects used a controller that exponentially stabilized trajectories. During continuous cup-and-ball displacements subjects developed predictable solutions sacrificing smoothness and energy efficiency. These results may stimulate control strategies for dexterous robotic manipulators and human–robot interaction.     

Participation of all Employee Categories in Innovation Processes in Slovak Organisations

Mobile Networks and Applications - Dynamically changing environment and the coming fourth industrial revolution represent a great challenge for businesses not only in Slovakia; and increasing...