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"Schröder, R."
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Shifting forms of continental colonialism : unfinished struggles and tensions
This book explores shifting forms of continental colonialism in Asia, Africa, Europe, and the Americas, from the early modern period to the present. It offers an interdisciplinary approach bringing together historians, anthropologists, and sociologists to contribute to a critical historical anthropology of colonialism. Though focused on the modern era, the volume illustrates that the colonial paradigm is a framework of theories and concepts that can be applied globally and deeply into the past. The chapters engage with a wide range of topics and disciplinary approaches from the theoretical to the empirical, deepening our understanding of under-researched areas of colonial studies and providing a cutting edge contribution to the study of continental and internal colonialism for all those interested in the global impact of colonialism on continents.
Book
Dimer ribbons of ATP synthase shape the inner mitochondrial membrane
ATP synthase converts the electrochemical potential at the inner mitochondrial membrane into chemical energy, producing the ATP that powers the cell. Using electron cryo‐tomography we show that the ATP synthase of mammalian mitochondria is arranged in long ∼1‐μm rows of dimeric supercomplexes, located at the apex of cristae membranes. The dimer ribbons enforce a strong local curvature on the membrane with a 17‐nm outer radius. Calculations of the electrostatic field strength indicate a significant increase in charge density, and thus in the local pH gradient of ∼0.5 units in regions of high membrane curvature. We conclude that the mitochondrial cristae act as proton traps, and that the proton sink of the ATP synthase at the apex of the compartment favours effective ATP synthesis under proton‐limited conditions. We propose that the mitochondrial ATP synthase organises itself into dimer ribbons to optimise its own performance.
Journal Article
The Relevance of Background Odor in Resource Location by Insects: A Behavioral Approach
Insects live in a highly complex odorant world. Within a variety of odor blends, they need to locate potential food sources, mates, and oviposition sites to gain reproductive success. In nature, volatile cues leading to a resource are always present with numerous other volatiles—here referred to as background odor—which may affect the parasitoid's response to resource-indicating cues. Three different types of background odor are discussed in this article: (a) irrelevant background odor, (b) background odor that may mask the resource-indicating signals, and (c) background odorants that may “sharpen the view” for resource-indicating odor and enhance the response to these. Odor orientation to resources especially in herbivorous and parasitic insects are addressed.
Journal Article
Force-producing ADP state of myosin bound to actin
Molecular motors produce force when they interact with their cellular tracks. For myosin motors, the primary force-generating state has MgADP tightly bound, whereas myosin is strongly bound to actin. We have generated an 8-Å cryoEM reconstruction of this state for myosin V and used molecular dynamics flexed fitting for model building. We compare this state to the subsequent state on actin (Rigor). The ADP-bound structure reveals that the actin-binding cleft is closed, even though MgADP is tightly bound. This state is accomplished by a previously unseen conformation of the β-sheet underlying the nucleotide pocket. The transition from the force-generating ADP state to Rigor requires a 9.5° rotation of the myosin lever arm, coupled to a β-sheet rearrangement. Thus, the structure reveals the detailed rearrangements underlying myosin force generation as well as the basis of strain-dependent ADP release that is essential for processive myosins, such as myosin V.
Journal Article
Proton gradients from light-harvesting E. coli control DNA assemblies for synthetic cells
Bottom-up and top-down approaches to synthetic biology each employ distinct methodologies with the common aim to harness living systems. Here, we realize a strategic merger of both approaches to convert light into proton gradients for the actuation of synthetic cellular systems. We genetically engineer
E. coli
to overexpress the light-driven inward-directed proton pump xenorhodopsin and encapsulate them in artificial cell-sized compartments. Exposing the compartments to light-dark cycles, we reversibly switch the pH by almost one pH unit and employ these pH gradients to trigger the attachment of DNA structures to the compartment periphery. For this purpose, a DNA triplex motif serves as a nanomechanical switch responding to the pH-trigger of the
E. coli
. When DNA origami plates are modified with the pH-sensitive triplex motif, the proton-pumping
E. coli
can trigger their attachment to giant unilamellar lipid vesicles (GUVs) upon illumination. A DNA cortex is formed upon DNA origami polymerization, which sculpts and deforms the GUVs. We foresee that the combination of bottom-up and top down approaches is an efficient way to engineer synthetic cells.
Controlled actuation is an important aspect of synthetic cellular systems. Here, the authors combine pH responsive DNA origami structures with light triggered proton pump engineered
E. coli
to trigger a change in pH and control the deformation of giant unilamellar vesicles by simple illumination.
Journal Article
Repetitive ultramicrotome trimming and SEM imaging for characterizing printed multilayer structures
Ultramicrotomy is a well-established technique that has been applied in biology and medical research to produce thin sections or a blockface of an embedded sample for microscopy. Recently, this technique has also been applied in materials science or micro- and nanotechnology as a sample preparation method for subsequent characterization. In this work, an application of ultramicrotomy for the cross-section preparation of an inkjet-printed multilayer structure is demonstrated. The investigated device is a capacitor consisting of three layers. The top and bottom electrodes are printed with silver nanoparticle ink and the dielectric layer with a ceramic nanoparticle/polymer ink. A 3D profilometer is initially used to study the surface morphology of the printed multilayer. The measurements show that both electrodes exhibit a coffee-ring effect, which results in an inhomogeneous layer structure of the device. To obtain precise 3D information on the multilayer, cross-sections must be prepared. Argon ion beam milling is the current gold standard to produce a single cross-section in good quality, however, the cross-section position within the multilayer volume is poorly defined. Moreover, the milling process requires a significant investment of time and resources. Herein, we develop an efficient method to realize repetitive cross-section preparation at well-defined positions in the multilayer volume. Repetitive cross-sections are exposed by trimming with an ultramicrotome (UM) and this blockface is subsequently transferred into a scanning electron microscope (SEM) for imaging. A combination of custom-modified UM and SEM specimen holders allows repeated transfer of the clamped multilayer sample between instruments without damage and with high positioning accuracy. This novel approach enhances the combination of an established ultramicrotome and a SEM for multilayer sample volume investigation. Thus, a comprehensive understanding of printed multilayer structures can be gained, to derive insights for optimization of device architecture and printing process.
Journal Article
Electron cryo-microscopy shows how strong binding of myosin to actin releases nucleotide
Muscle contraction involves the cyclic interaction of the myosin cross-bridges with the actin filament, which is coupled to steps in the hydrolysis of ATP
1
. While bound to actin each cross-bridge undergoes a conformational change, often referred to as the “power stroke”
2
, which moves the actin filament past the myosin filaments; this is associated with the release of the products of ATP hydrolysis and a stronger binding of myosin to actin. The association of a new ATP molecule weakens the binding again, and the attached cross-bridge rapidly dissociates from actin. The nucleotide is then hydrolysed, the conformational change reverses, and the myosin cross-bridge reattaches to actin. X-ray crystallography has determined the structural basis of the power stroke, but it is still not clear why the binding of actin weakens that of the nucleotide and vice versa. Here we describe, by fitting atomic models of actin and the myosin cross-bridge into high-resolution electron cryo-microscopy three-dimensional reconstructions, the molecular basis of this linkage. The closing of the actin-binding cleft when actin binds is structurally coupled to the opening of the nucleotide-binding pocket.
Journal Article
3D Printing Hierarchically Nano‐Ordered Structures
Natural materials are composed of a limited number of molecular building blocks and their exceptional properties are governed by their hierarchical structure. However, this level of precision is unattainable with current state‐of‐the‐art materials for 3D printing. Herein, new self‐assembled printable materials based on block copolymers (BCPs) enabling precise control of the nanostructure in 3D are presented. In particular, well‐defined BCPs consisting of poly(styrene) (PS) and a polymethacrylate‐based copolymer decorated with printable units are selected as suitable self‐assembled materials and synthesized using controlled radical polymerization. The synthesized library of BCPs are utilized as printable formulations for the fabrication of complex 3D microstructures using two‐photon laser printing. By fine‐tuning the BCP composition and solvent in the formulations, the fabrication of precise 3D nano‐ordered structures is demonstrated for the first time. A key point of this work is the achievement of controlled nano‐order within the entire 3D structures. Thus, imaging of the cross‐sections of the 3D printed samples is performed, enabling the visualization also from the inside. The presented versatile approach is expected to create new avenues for the precise design of functional polymer materials suitable for high‐resolution 3D printing exhibiting tailor‐made nanostructures.
Journal Article
Two-step absorption instead of two-photon absorption in 3D nanoprinting
The quadratic optical nonlinearity arising from two-photon absorption provides the crucial spatial concentration of optical excitation in three-dimensional (3D) laser nanoprinting, with widespread applications in technical and life sciences. Femtosecond lasers allow for obtaining efficient two-photon absorption but are accompanied by a number of issues, including higher-order processes, cost, reliability and size. Here we introduce two-step absorption replacing two-photon absorption as the primary optical excitation process. Under suitable conditions, two-step absorption shows the same quadratic optical nonlinearity as two-photon absorption. We present a photoresist system based on a photoinitiator supporting two-step absorption, a scavenger and a well-established triacrylate. We show that this system allows for printing state-of-the-art 3D nanostructures and beyond. In these experiments, we use ~100 μW optical power from an inexpensive, compact continuous-wave semiconductor laser diode emitting at 405 nm wavelength. Our work opens the door to drastic miniaturization and cost reduction of 3D laser nanoprinters.As an alternative to high-resolution fabrication by two-photon absorption, researchers demonstrate a two-step absorption process that employs inexpensive light sources.
Journal Article