11 research outputs found
Exploring cavity dynamics in biomolecular systems
Background The internal cavities of proteins are dynamic structures and their
dynamics may be associated with conformational changes which are required for
the functioning of the protein. In order to study the dynamics of these
internal protein cavities, appropriate tools are required that allow rapid
identification of the cavities as well as assessment of their time-dependent
structures. Results In this paper, we present such a tool and give results
that illustrate the applicability for the analysis of molecular dynamics
trajectories. Our algorithm consists of a pre-processing step where the
structure of the cavity is computed from the Voronoi diagram of the van der
Waals spheres based on coordinate sets from the molecular dynamics trajectory.
The pre-processing step is followed by an interactive stage, where the user
can compute, select and visualize the dynamic cavities. Importantly, the tool
we discuss here allows the user to analyze the time-dependent changes of the
components of the cavity structure. An overview of the cavity dynamics is
derived by rendering the dynamic cavities in a single image that gives the
cavity surface colored according to its time-dependent dynamics. Conclusion
The Voronoi-based approach used here enables the user to perform accurate
computations of the geometry of the internal cavities in biomolecules. For the
first time, it is possible to compute dynamic molecular paths that have a
user-defined minimum constriction size. To illustrate the usefulness of the
tool for understanding protein dynamics, we probe the dynamic structure of
internal cavities in the bacteriorhodopsin proton pump
First PACSâintegrated artificial intelligenceâbased software tool for rapid and fully automatic analysis of body composition from CT in clinical routine
Background: To externally evaluate the first picture archiving communications system (PACS)-integrated artificial intelligence (AI)-based workflow, trained to automatically detect a predefined computed tomography (CT) slice at the third lumbar vertebra (L3) and automatically perform complete image segmentation for analysis of CT body composition and to compare its performance with that of an established semi-automatic segmentation tool regarding speed and accuracy of tissue area calculation.
Methods: For fully automatic analysis of body composition with L3 recognition, U-Nets were trained (Visage) and compared with a conventional image segmentation software (TomoVision). Tissue was differentiated into psoas muscle, skeletal muscle, visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT). Mid-L3 level images from randomly selected DICOM slice files of 20 CT scans acquired with various imaging protocols were segmented with both methods.
Results: Success rate of AI-based L3 recognition was 100%. Compared with semi-automatic, fully automatic AI-based image segmentation yielded relative differences of 0.22% and 0.16% for skeletal muscle, 0.47% and 0.49% for psoas muscle, 0.42% and 0.42% for VAT and 0.18% and 0.18% for SAT. AI-based fully automatic segmentation was significantly faster than semi-automatic segmentation (3 ± 0 s vs. 170 ± 40 s, P < 0.001, for User 1 and 152 ± 40 s, P < 0.001, for User 2).
Conclusion: Rapid fully automatic AI-based, PACS-integrated assessment of body composition yields identical results without transfer of critical patient data. Additional metabolic information can be inserted into the patientâs image report and offered to the referring clinicians
Visuelle Analyse atomarer Strukturen basierend auf dem Modell harter Kugeln
Visualization and Analysis of atomic compositions is essential to understand
the structure and functionality of molecules. There exist versatile areas of
applications, from fundamental researches in biophysics and materials science
to drug development in pharmaceutics. For most applications, the hard-sphere
model is the most often used molecular model. Although the model is a quite
simple approximation of reality, it enables investigating important physical
properties in a purely geometrical manner. Furthermore, large data sets with
thousands up to millions of atoms can be visualized and analyzed. In addition
to an adequate and efficient visualization of the data, the extraction of
important structures plays a major role. For the investigation of
biomolecules, such as proteins, especially the analysis of cavities and their
dynamics is of high interest. Substrates can bind in cavities, thereby
inducing changes in the function of the protein. Another example is the
transport of substrates through membrane proteins by the dynamics of the
cavities. For both, the visualization as well as the analysis of cavities, the
following contributions will be presented in this thesis: 1\. The rendering of
smooth molecular surfaces for the analysis of cavities is accelerated and
visually improved, which allows showing dynamic proteins. On the other hand,
techniques are proposed to interactively render large static biological
structures and inorganic materials up to atomic resolution for the first time.
2\. A Voronoi-based method is presented to extract molecular cavities. The
procedure comes with a high geometrical accuracy by a comparatively fast
computation time. Additionally, new methods are presented to visualize and
highlight the cavities within the molecular structure. In a further step, the
techniques are extended for dynamic molecular data to trace cavities over time
and visualize topological changes. 3\. To further improve the accuracy of the
approaches mentioned above, a new molecular surface model is presented that
shows the accessibility of a substrate. For the first time, the structure and
dynamics of the substrate as hard-sphere model is considered for the
accessibility computation. In addition to the definition of the surface, an
efficient algorithm for its computation is proposed, which additionally allows
extracting cavities. The presented algorithms are demonstrated on different
molecular data sets. The data sets are either the result of physical or
biological experiments or molecular dynamics simulations.Die Visualisierung und Analyse atomarer Strukturen ist essenziell fĂŒr das
VerstĂ€ndnis des Aufbaus und der Funktionsweise von MolekĂŒlen. Es gibt
vielfÀltige Anwendungsgebiete, angefangen von Grundlagenforschungen in der
Biophysik und den Materialwissenschaften bis hin zur Medikamentenentwicklung
in der Pharmazie. Das Modell harter Kugeln, auch Kalottenmodell genannt, ist
dabei das am hĂ€ufigsten verwendete MolekĂŒlmodell. Obwohl es ein sehr
vereinfachtes Modell ist, ermöglicht es die geometrische Betrachtung wichtiger
physikalischer Eigenschaften und erlaubt zudem, groĂe Daten mit Tausenden bis
hin zu Millionen von Atomen darzustellen und zu analysieren. Neben einer
adequaten und performanten Visualisierung der Daten spielt vor allem die
Extraktion von Strukturen eine groĂe Rolle. Bei der Untersuchung von
BiomolekĂŒlen, wie Proteinen, ist besonders die Analyse und Dynamik der
KavitĂ€ten von groĂem Interesse. In den KavitĂ€ten können Substrate binden, die
damit die Funktionsweise eines Proteins Àndern, oder sie können durch die
Dynamik der KavitĂ€ten durch Membranen transportiert werden. Sowohl fĂŒr die
Visualisierung als auch fĂŒr die Analyse der KavitĂ€ten werden in dieser
Dissertation die folgenden BeitrÀge geleistet: 1\. Zum einen wird die
Darstellung glatter OberflĂ€chen, die sich fĂŒr die Analyse von KavitĂ€ten
eignen, beschleunigt und visuell verbessert, wodurch sie auf dynamische
Proteine angewendet werden können. Zum anderen werden Methoden vorgestellt,
die erstmals erlauben groĂe statische biologische Strukturen und anorganische
Materialien bis auf atomare Auflösung interaktiv darzustellen. 2\. FĂŒr die
Extraktion von KavitÀten wird ein Voronoi-basiertes Verfahren mit einer hohen
geometrischen Genaugkeit bei einer vergleichsweise hohen Geschwindigkeit
vorgestellt. Dazu werden neue Methoden prÀsentiert, welche die KavitÀten
innerhalb der molekularen Struktur darstellen und hervorheben. Des Weiteren
werden die Methoden fĂŒr dynamische Daten erweitert, um KavitĂ€ten ĂŒber die Zeit
verfolgen und topologische VerÀnderungen visualisieren zu können. 3\. Um die
Genauigkeit der oben genannten Verfahren weiter voranzutreiben, wird eine neue
MolekĂŒloberflĂ€che vorgestellt, welche die erreichbaren Regionen eines
Substrates zeigt. Dabei wird erstmals die Struktur und Dynamik des Substrates
in Form des Kalottenmodells berĂŒcksichtigt. Neben der Definition der
OberflĂ€che wird ein effizienter Algorithmus fĂŒr dessen Berechnung prĂ€sentiert,
der es zudem erlaubt KavitÀten zu extrahieren. Die vorgestellten Algorithmen
werde an verschiedenen molekularen Daten demonstriert. Die Daten sind das
Ergebnis physikalischer und biologischer Experimente oder stammen aus
molekularen Simulationen
Where is the West Antarctic Rift System in the Amundsen Sea and Bellingshausen Sea sectors?
The West Antarctic Rift System (WARS) is one of the largest continental rifts globally, but its lateral extent, distribution of local rifts, timing of rifting phases, and mantle processes are still largely enigmatic. It has been presumed that the rift and its crustal extensional processes have widely controlled the history and development of West Antarctic glaciation with an ice sheet of which most is presently based at sub-marine level and which is, therefore, likely to be highly sensitive to ocean warming. While the western domain of the WARS in the Ross Sea has been studied in some detail, only recently have various geophysical and geochemical/thermochronological analyses revealed indications for its eastern extent in the Amundsen Sea and Bellingshausen Sea sectors of the South Pacific realm. The current model, based on these studies and additional data, suggests that the WARS activity included tectonic translateral, transtensional and extensional processes from the Amundsen Sea Embayment to the Bellingshausen Sea region of the southern Antarctic Peninsula. We present the range of existing hypotheses regarding the extent of the eastern WARS as well as published and yet unpublished data that support a conceptual WARS model for the eastern West Antarctica with implications for glacial onset and developments
The extent of the West Antarctic Rift System in the Amundsen Sea and Bellingshausen Sea sectors
The West Antarctic Rift System (WARS) is one of the largest continental rifts globally, but its lateral extent, distribution of local rifts, timing of rifting phases, and mantle processes are still largely enigmatic. It has been presumed that the rift and its crustal extensional processes have widely controlled the history and development of West Antarctic glaciation with an ice sheet of which most is presently based at sub-marine level and which is, therefore, likely to be highly sensitive to ocean warming. While the western domain of the WARS in the Ross Sea has been studied in some detail, only recently have various geophysical and geochemical/thermochronological analyses revealed indications for its eastern extent in the Amundsen Sea and Bellingshausen Sea sectors of the South Pacific realm and in the eastern Marie Byrd Land, Ellsworth Land, Thurston Island and Antarctic Peninsula crustal blocks. One of the current models, based on these studies and additional data, suggests that the WARS activity included tectonic translateral, transtensional and extensional processes from the Amundsen Sea Embayment to the Bellingshausen Sea region of the southern Antarctic Peninsula, basically following the eastward migrating collision of the Phoenix Plate with the Antarctic Plate. We present the range of existing and novel hypotheses regarding the extent of the eastern WARS as well as published and yet unpublished data that support a conceptual WARS model for West Antarctica with implications for glacial onset and developments
Virtual unfolding of folded papyri
The historical importance of ancient manuscripts is unique since they provide information about the heritage of ancient cultures. Often texts are hidden in rolled or folded documents. Due to recent improvements in sensitivity and resolution, spectacular disclosures of rolled hidden texts were possible by X-ray tomography. However, revealing text on folded manuscripts is even more challenging. Manual unfolding is often too risky in view of the fragile condition of fragments, as it can lead to the total loss of the document. X-ray tomography allows for virtual unfolding and enables non-destructive access to hidden texts. We have recently demonstrated the procedure and tested unfolding algorithms on a mockup sample. Here, we present results on unfolding ancient papyrus packages from the papyrus collection of the MusĂ©e du Louvre, among them objects folded along approximately orthogonal folding lines. In one of the packages, the first identification of a word was achieved, the Coptic word for âLordâ
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Membrane Protein Structure, Function, and Dynamics: a Perspective from Experiments and Theory
Membrane proteins mediate processes that are fundamental for the flourishing of biological cells. Membrane-embedded transporters move ions and larger solutes across membranes; receptors mediate communication between the cell and its environment and membrane-embedded enzymes catalyze chemical reactions. Understanding these mechanisms of action requires knowledge of how the proteins couple to their fluid, hydrated lipid membrane environment. We present here current studies in computational and experimental membrane protein biophysics, and show how they address outstanding challenges in understanding the complex environmental effects on the structure, function, and dynamics of membrane proteins