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Pathogenic Gram-negative bacteria use a type three secretion system (TTSS) to deliver virulence factors into host cells. Although the order in which proteins incorporate into the growing TTSS is well described, the underlying assembly mechanisms are still unclear. Here we show that the TTSS needle protomer refolds spontaneously to extend the needle from the distal end. We developed a functional mutant of the needle protomer from Shigella flexneri and Salmonella typhimurium to study its assembly in vitro. We show that the protomer partially refolds from α-helix into β-strand conformation to form the TTSS needle. Reconstitution experiments show that needle growth does not require ATP. Thus, like the structurally related flagellar systems, the needle elongates by subunit polymerization at the distal end but requires protomer refolding. Our studies provide a starting point to understand the molecular assembly mechanisms and the structure of the TTSS at atomic level.
The investigation of an ancient Chinese ceramic served to further develop and validate fundamental parameter-based quantitation procedures in reference-free x-ray fluorescence (XRF) analysis. The XRF measurements of this sample were performed at the four-crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt (PTB) at the BESSY II synchrotron radiation facility employing different excitation energies. The parallel processing of the XRF spectra recorded at different excitation energies provides a means to simultaneously evaluate relevant fundamental parameters and secondary enhancement processes such as those induced by photoelectrons. Employing well-characterized and absolutely calibrated instrumentation, all experimental parameters involved in XRF are known for small relative uncertainties allowing for a completely reference-free quantitation. Apart from traces of rare earth elements, the analytical results of the Chinese ceramic achieved by reference-free XRF are in line with target values given within a proficiency test of the International Atomic Energy Agency (IAEA) involving atomic and nuclear methods.
Eine besondere angewandte Fertigungstechnik stellt die Explosivumformung dar. Deren Grundlagen vom Detonationsvorgang, der Energieübertragung und -umsetzung sowie des Werkstoffverhaltens werden beschrieben. Aufgezeigt werden Vorteile des Explosivplattierens von Metallen und Bauteilen gegenüber anderen Fertigungsverfahren und deren Anwendung insbesondere für Motorenbauteile.