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Berlin, Germany

The Humboldt University of Berlin is one of Berlin's oldest universities, founded in 1810 as the University of Berlin by the liberal Prussian educational reformer and linguist Wilhelm von Humboldt, whose university model has strongly influenced other European and Western universities. From 1828 it was known as the Frederick William University , and later also as the Universität unter den Linden after its location. In 1949, it changed its name to Humboldt-Universität in honour of both its founder Wilhelm and his brother, geographer Alexander von Humboldt.In 2012, the Humboldt University of Berlin was one of eleven German universities to win in the German Universities Excellence Initiative, a national competition for universities organized by the German Federal Government. The university has educated 29 nobel prize winners and is considered one of the most prestigious universities in Europe overall as well as one of the most prestigious universities worldwide for arts and humanities. Wikipedia.

Dobbek H.,Humboldt University of Berlin
Coordination Chemistry Reviews | Year: 2011

This review provides an overview of the contributions of protein X-ray crystallography to the field of pyranopterin-containing W/Mo-enzymes. Several crystal structures for all of the four different families of pyranopterin-containing enzymes have been determined in recent years allowing one to compare overall folds and active site architectures. Especially within the dimethylsulfoxide reductase family and the Mo-containing hydroxylases a diversity of Mo/W-ligands has been discovered, challenging the earlier proposed functions of individual active site components. Reinterpretations of structures and the use of enzyme variants and complexes with inhibitors and slow substrate provided further insights, which will be discussed for the individual enzymes. © 2010 Elsevier B.V. Source

Brettschneider C.,Humboldt University of Berlin
Molecular systems biology | Year: 2010

The circadian rhythm of the cyanobacterium Synechococcus elongatus is controlled by three proteins, KaiA, KaiB, and KaiC. In a test tube, these proteins form complexes of various stoichiometry and the average phosphorylation level of KaiC exhibits robust circadian oscillations in the presence of ATP. Using mathematical modeling, we were able to reproduce quantitatively the experimentally observed phosphorylation dynamics of the KaiABC clockwork in vitro. We thereby identified a highly non-linear feedback loop through KaiA inactivation as the key synchronization mechanism of KaiC phosphorylation. By using the novel method of native mass spectrometry, we confirm the theoretically predicted complex formation dynamics and show that inactivation of KaiA is a consequence of sequestration by KaiC hexamers and KaiBC complexes. To test further the predictive power of the mathematical model, we reproduced the observed phase synchronization dynamics on entrainment by temperature cycles. Our model gives strong evidence that the underlying entrainment mechanism arises from a temperature-dependent change in the abundance of KaiAC and KaiBC complexes. Source

Rudiger S.,Humboldt University of Berlin
Physics Reports | Year: 2014

Cellular signaling operates in a noisy environment shaped by low molecular concentrations and cellular heterogeneity. For calcium release through intracellular channels-one of the most important cellular signaling mechanisms-feedback by liberated calcium endows fluctuations with critical functions in signal generation and formation. In this review it is first described, under which general conditions the environment makes stochasticity relevant, and which conditions allow approximating or deterministic equations. This analysis provides a framework, in which one can deduce an efficient hybrid description combining stochastic and deterministic evolution laws. Within the hybrid approach, Markov chains model gating of channels, while the concentrations of calcium and calcium binding molecules (buffers) are described by reaction-diffusion equations. The article further focuses on the spatial representation of subcellular calcium domains related to intracellular calcium channels. It presents analysis for single channels and clusters of channels and reviews the effects of buffers on the calcium release. For clustered channels, we discuss the application and validity of coarse-graining as well as approaches based on continuous gating variables (Fokker-Planck and chemical Langevin equations). Comparison with recent experiments substantiates the stochastic and spatial approach, identifies minimal requirements for a realistic modeling, and facilitates an understanding of collective channel behavior. At the end of the review, implications of stochastic and local modeling for the generation and properties of cell-wide release and the integration of calcium dynamics into cellular signaling models are discussed. © 2013. Source

Hoare B.,Humboldt University of Berlin
Nuclear Physics B | Year: 2015

We construct a two-parameter deformation of the Metsaev-Tseytlin action for supercosets with isometry group of the form Ĝ×Ĝ. The resulting action is classically integrable and is Poisson-Lie symmetric suggesting that the symmetry of the model is q-deformed, uqL(Ĝ) × uqR(Ĝ). Focusing on the cases relevant for strings moving in AdS3×S3×T4 and AdS3×S3×S3×S1, we analyze the corresponding deformations of the AdS3 and S3 metrics. We also construct a two-parameter q-deformation of the u(1) ∈ psu(1|1)2⋉u(1)⋉ℝ3-invariant R-matrix and closure condition, which underlie the light-cone gauge S-matrix and dispersion relation of the aforementioned string theories. With the appropriate identification of parameters, the near-BMN limit of the dispersion relation is shown to agree with that found from the deformed supercoset sigma model. © 2014 The Author. Published by Elsevier B.V. All rights reserved. Source

Sierka M.,Humboldt University of Berlin
Progress in Surface Science | Year: 2010

In this paper, I review recent progress in joint theoretical and experimental studies aiming at atomic structure determination of low-dimensional metal oxides. Low-dimensional systems can be generally defined as materials of unusual structure that extend to less than three dimensions. In recent years low-dimensional systems have attracted increasing attention of physicists and chemists, and the interest is expected to rise in the near future. Two- and one-dimensional structures in form of thin oxide films or elongated oxide chains have many potential applications including model supports for heterogeneous catalysts and insulating layers in semiconductor industry. The interest in zero-dimensional gas-phase oxide clusters ranges from astrophysics to studies of elementary steps in catalysis. The key prerequisite for understanding physical and chemical properties of low-dimensional systems is a detailed knowledge of their atomic structures. However, such systems frequently present complex structures to solve. Only in a few cases experimental data can provide some information about possible arrangement of atoms, but data interpretation relies to a large extent on intuition. Therefore, in the recent years quantum chemical calculations became an indispensable tool in structure identification of low-dimensional systems, yet the accuracy of theoretical tools is often limited. The results reviewed here demonstrate that often the only way of an unambiguous atomic structure determination of low-dimensional systems are experimental studies combined with theoretical calculations. Particularly the global optimization methods such as genetic algorithm in combination with the density functional theory prove very useful in automatic structure determination of the observed surface structures and gas-phase clusters. © 2010 Elsevier Ltd. All rights reserved. Source

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