914 research outputs found
Microtubule dynamics are defined by conformations and stability of clustered protofilaments
No full textMicrotubules are dynamic cytoskeletal polymers that add and lose tubulin dimers at their ends. Microtubule growth, shortening and transitions between them are linked to GTP hydrolysis. Recent evidence suggests that flexible tubulin protofilaments at microtubule ends adopt a variety of shapes, complicating structural analysis using conventional techniques. Therefore, the link between GTP hydrolysis, protofilament structure and microtubule polymerization state is poorly understood. Here, we investigate the conformational dynamics of microtubule ends using coarse-grained modeling supported by atomistic simulations and cryo-electron tomography. We show that individual bent protofilaments organize in clusters, transient precursors to a straight
microtubule lattice, with GTP-bound ends showing elevated and more persistent cluster formation. Differences in the mechanical properties of GTP- and GDP-protofilaments result in differences in intra-cluster tension, determining both clustering propensity and protofilament length. We propose that conformational selection at microtubule ends favors long-lived clusters of short GTP-protofilaments that are more prone to form a straight microtubule lattice and accommodate new tubulin dimers. Conversely, microtubule ends trapped in states with
unevenly long and stiff GDP-protofilaments are more prone to shortening. We conclude that protofilament clustering is a key phenomenon that links the hydrolysis state of single tubulins to the polymerization state of the entire microtubule
Kinetics, statistics, and energetics of lipid membrane electroporation studied by molecular dynamics simulations
No full textBoeckmann RA, de Groot BL, Kakorin S, Neumann E, Grubmueller H. Kinetics, statistics, and energetics of lipid membrane electroporation studied by molecular dynamics simulations. BIOPHYSICAL JOURNAL. 2008;95(4):1837-1850.Membrane electroporation is the method to directly transfer bioactive substances such as drugs and genes into living cells, as well as preceding electrofusion. Although much information on the microscopic mechanism has been obtained both from experiment and simulation, the existence and nature of possible intermediates is still unclear. To elucidate intermediates of electropore formation by direct comparison with measured prepore formation kinetics, we have carried out 49 atomistic electroporation simulations on a palmitoyl-oleoyl-phosphatidylcholine bilayer for electric field strengths between 0.04 and 0.7 V/nm. A statistical theory is developed to facilitate direct comparison of experimental (macroscopic) prepore formation kinetics with the (single event) preporation times derived from the simulations, which also allows us to extract an effective number of lipids involved in each pore formation event. A linear dependency of the activation energy for prepore formation on the applied field is seen, with quantitative agreement between experiment and simulation. The distribution of preporation times suggests a four-state pore formation model. The model involves a first intermediate characterized by a differential tilt of the polar lipid headgroups on both leaflets, and a second intermediate (prepore), where a polar chain across the bilayer is formed by 3-4 lipid headgroups and several water molecules, thereby providing a microscopic explanation for the polarizable volume derived previously from the measured kinetics. An average pore radius of 0.47 +/- 0.15 nm is seen, in favorable agreement with conductance measurements and electrooptical experiments of lipid vesicles
From Helmut Jürgensen’s former students: The game of informatics
No full textPersonal reflections are given on being students of Helmut Jürgensen. Then, we attempt
to address his hypothesis that informatics follows trend-like behaviours through the
use of a content analysis of university job advertisements, and then via simulation
techniques from the area of quantitative economics
Smalltalk Interpreter in Java
No full textAuthor Helmut Rohregger, BSc.Kurzfassungen in deutscher und englischer SpracheMasterarbeit Universität Linz 201
Smalltalk Interpreter in Java
No full textAuthor Helmut Rohregger, BSc.Kurzfassungen in deutscher und englischer SpracheMasterarbeit Universität Linz 201
HELMUT E. LUCK JAKO HISTORYK PSYCHOLOGII
No full textThe article presents the figure of Helmut E. Luck, well-known scientist in the world of historians of psychology. Helmut E. Luck also is well-known in Poland, as the author or the scientific editor of several books in the field of history of psychology. In the first part of the article the short presentation of his scientific career and his scientific achievements are demonstrated. The second part comprises the analysis of his opinions in the scope of social psychology. Helmut E. Luck was the one of pioneers in psychology, who paid attention to social positive phenomena or social positive behaviors. In the field of history of psychology, H.E.Luck made the contribution to methodological analysis of psychological ideas in history, preferring the model which underlines connection of psychology with culture and at the same time creates the opportunity to analysis of biographical plots. The article also shows unquestionable and unusually merits of Luck’s in popularization of knowledge about history of psychology.The article presents the figure of Helmut E. Luck, well-known scientist in the world of historians of psychology. Helmut E. Luck also is well-known in Poland, as the author or the scientific editor of several books in the field of history of psychology. In the first part of the article the short presentation of his scientific career and his scientific achievements are demonstrated. The second part comprises the analysis of his opinions in the scope of social psychology. Helmut E. Luck was the one of pioneers in psychology, who paid attention to social positive phenomena or social positive behaviors. In the field of history of psychology, H.E.Luck made the contribution to methodological analysis of psychological ideas in history, preferring the model which underlines connection of psychology with culture and at the same time creates the opportunity to analysis of biographical plots. The article also shows unquestionable and unusually merits of Luck’s in popularization of knowledge about history of psychology
Conformational Dynamics and Functional Asymmetry of ABCE1, a Ribosome Recycling Protein
No full textDie IPrA, Helmut und ich
No full textThis contribution describes the beginning and the development of the professional and personal relationship between Helmut and the author which has been highly influenced by our joint membership in the International Pragmatics Association and by our activities in and for the IPrA
- …
