Modeling of Candida antarctica lipase B under non-natural conditions

Candida antarctica Lipase B (CALB) ist ein für die Biokatalyse wichtiges Enzym, das für die Herstellung von Emulgatoren, Körperpflegeprodukten, Kosmetikartikeln, Geschmacksstoffen und Medikamenten verwendet wird. Allerdings wird diese Lipase durch einige organische Lösungsmittel wie z. B. Methanol bereits bei geringen Konzentrationen inaktiviert, während sie bei deutlich höheren Konzentrationen anderer organischer Lösungsmittel wie z. B. Ethanol noch aktiv ist. Dies ist ein Problem bei Reaktionen, bei denen Methanol als Substrat dient und in hohen Konzentrationen zugegeben wird. Im Zuge dieser Arbeit sollte der Einfluss von organischen Lösungsmitteln auf CALB sowie die Inaktivierung und der zugrunde liegende Mechanismus durch molekulardynamische Simulationen untersucht werden.Lipases like Candida antarctica lipase B (CALB) are important enzymes in biocatalysis and widely used for the preparation of emulsifiers, of personal care and cosmetic products, of flavours and pharmaceuticals. However, they are already inactivated by moderate methanol concentrations, while they are able to tolerate much higher ethanol concentrations. This is problematic, when methanol is used as a substrate in the respective reaction and thus added in high concentrations. To study the effect of organic solvents on CALB as well as the molecular mechanism of the inactivation, molecular dynamics simulations of CALB were performed

Verfahren zur Vereinzelung von Fasern sowie Vorrichtung zu seiner Durchfuehrung

Bei einem Verfahren zur Vereinzelung von Fasern aus einem Faserbuendel wird das Faserbuendel als Ganzes zwischen zwei im Abstand voneinander angeordnete Elektroden gebracht und auf einer der Elektroden positioniert. Anschliessend wird ein elektrisches Gleichspannungsfeld an die Elektroden gelegt, dessen Staerke so bemessen ist, dass die das Faserbuendel bildenden Fasern in Richtung auf die zweite Elektrode beschleunigt und von dieser reflektiert werden. Die dadurch vereinzelten Fasern werden in einer Auffangeinrichtung gesammelt. Eine Vorrichtung zur Durchfuehrung dieses Verfahrens besteht aus zwei uebereinander angeordneten flaechigen Elektroden sowie einer unter diesen befindlichen Auffangeinrichtung

Binding of Solvent Molecules to a Protein Surface in Binary Mixtures Follows a Competitive Langmuir Model

The binding of solvent molecules to a protein surface was modeled by molecular dynamics simulations of of <i>Candida antarctica</i> (<i>C. antarctica</i>) lipase B in binary mixtures of water, methanol, and toluene. Two models were analyzed: a competitive Langmuir model which assumes identical solvent binding sites with a different affinity toward water (<i>K</i>_Wat), methanol (<i>K</i>_Met), and toluene (<i>K</i>_Tol) and a competitive Langmuir model with an additional interaction between free water and already bound water (<i>K</i>_WatWat). The numbers of protein-bound molecules of both components of a binary mixture were determined for different compositions as a function of their thermodynamic activities in the bulk phase, and the binding constants were simultaneously fitted to the six binding curves (two components of three different mixtures). For both Langmuir models, the values of <i>K</i>_Wat, <i>K</i>_Met, and <i>K</i>_Tol were highly correlated. The highest binding affinity was found for methanol, which was almost 4-fold higher than the binding affinities of water and toluene (<i>K</i>_Met ≫ <i>K</i>_Wat ≈ <i>K</i>_Tol). Binding of water was dominated by the water–water interaction (<i>K</i>_WatWat). Even for the three protein surface patches of highest water affinity, the binding affinity of methanol was 2-fold higher than water and 8-fold higher than toluene (<i>K</i>_Met > <i>K</i>_Wat > <i>K</i>_Tol). The Langmuir model provides insights into the protein destabilizing mechanism of methanol which has a high binding affinity toward the protein surface. Thus, destabilizing solvents compete with intraprotein interactions and disrupt the tertiary structure. In contrast, benign solvents such as water or toluene have a low affinity toward the protein surface. Water is a special solvent: only few water molecules bind directly to the protein; most water molecules bind to already bound water molecules thus forming water patches. A quantitative mechanistic model of protein–solvent interactions that includes competition and miscibility of the components contributes a robust basis for solvent and protein engineering

Verfahren zur Bestimmung der Qualitaet eines Kristallgemisches, insbesondere von Zucker, sowie Vorrichtung zur Durchfuehrung eines solchen Verfahrens

The process determines the quality of a crystal mixture, especially of sugar. A characteristic of one of the crystals in the two-component mixture is measured to assess the mixture quality. At a computer (8) the measurement is compared with a stored desired value, a yardstick for the required mixture quality. In accordance with the result, the ratio of the components is adjusted. Also claimed is the device for the above process. A line (3) carrying the solution is followed by a crystalliser. Two further supply lines (1,2) for the components, feed the line (3). The supply lines have flow controls (4,5) connected to a computer unit (8), receiving the output of a sensor in the line. USE - Used to determine the quality of a sugar solution. ADVANTAGE - An early and reliable indication of the quality of the crystal mixture can be obtained. Continuous measurement is achieved. Standard control methodology and measurements are used

Molecular modelling of the mass density of single proteins

<div><p>Using molecular dynamics (MD) simulations, the density of single proteins and its temperature dependence was modelled starting from the experimentally determined protein structure and a generic, transferable force field, without the need of prior parameterization. Although all proteins consist of the same 20 amino acids, their density in aqueous solution varies up to 10% and the thermal expansion coefficient up to twofold. To model the protein density, systematic MD simulations were carried out for 10 proteins with a broad range of densities (1.32–1.43 g/cm³) and molecular weights (7–97 kDa). The simulated densities deviated by less than 1.4% from their experimental values that were available for four proteins. Further analyses of protein density showed that it can be essentially described as a consequence of amino acid composition. For five proteins, the density was simulated at different temperatures. The simulated thermal expansion coefficients ranged between 4.3 and 7.1 × 10⁻⁴ K⁻¹ and were similar to the experimentally determined values of ribonuclease-A and lysozyme (deviations of 2.4 and 14.6%, respectively). Further analyses indicated that the thermal expansion coefficient is linked to the temperature dependence of atomic fluctuations: proteins with a high thermal expansion coefficient show a low increase in flexibility at increasing temperature. A low increase in atomic fluctuations with temperature has been previously described as a possible mechanism of thermostability. Thus, a high thermal expansion coefficient might contribute to protein thermostability.</p> </div