University of Konstanz

About: University of Konstanz is a education organization based out in Konstanz, Baden-Württemberg, Germany. It is known for research contribution in the topics: Population & Membrane. The organization has 12115 authors who have published 27401 publications receiving 951162 citations. The organization is also known as: University of Constance & Universität Konstanz.

Systematic study of insulator-metal transitions in perovskites RNiO3 (R=Pr,Nd,Sm,Eu) due to closing of charge-transfer gap.

Abstract: The detailed behavior of the phase transitions was mapped out for the series R${\mathrm{NiO}}_{3}$ as a function of the rare earth (R). A sharp insulator-metal transition is observed, which depends strongly on R.Forsmall$R it occurs at a higher temperature than the antiferromagnetic ordering (measured by muon-spin relaxation). By increasing either the temperature or the size of R, an insulator-metal transition is observed, most probably caused by the closing of the charge-transfer gap, induced by increase in the electronic bandwidth.

Functional Aptamers and Aptazymes in Biotechnology, Diagnostics, and Therapy

Abstract: Aptamers are single-stranded nucleic acid molecules that possess properties comparable to those of protein monoclonal antibodies, and thus are clear alternatives to long established antibody-based diagnostic or biotechnological products for research, diagnostics, and therapy. 1-4 This class of functional nucleic acids can fold into complex three-dimensional shapes, 5-7 forming binding pockets and clefts for the specific recognition and tight binding of any given molecular target, 8-10 from metal ions and small chemicals to large proteins and higher order protein complexes, whole cells, viruses, or parasites. Aptamers can be isolated in Vitro from vast combinatorial libraries that comprise trillions of different sequences, by a process called “ in Vitro selection”, or “SELEX”, an acronym for “systematic evolution of ligands by exponential enrichment”. An in Vitro selection experiment comprises a number of sequential steps, the first of which is the generation of a nucleic acid library of random sequences. This starting pool of mainly nonfunctional RNA or DNA sequences is generated using a standard DNA-oligonucleotide synthesizer. 11 The design of such libraries involves the synthesis of a short defined sequence, followed by a random region of variable length and another defined sequence at the 5 ′-end. This pool of synthetic single-stranded DNA (ssDNA) is amplified in the polymerase chain reaction (PCR), generating several copies of each DNA in its double-stranded form. By in Vitro transcription, a corresponding library of RNA molecules can be generated which can then be used for the in Vitro selection. If the transcription reaction contains nucleoside triphosphate derivatives that are chemically modified but still are substrates for RNA polymerases, libraries of modified RNAs can be generated in which sequences are equipped with a broad variety of additional chemical functionalities, normally not present in natural nucleic acids. 12-14 Aptamers selected from chemically modified libraries can, in some cases, be completely resistant toward degradation by nucleases. The additional functional groups can lead to ligands with novel * To whom correspondence should be addressed: telephone, +49-228735661; fax,+49-228-735388; e-mail, m.famulok@uni-bonn.de. † LIMES Institute. ‡ University of Konstanz. Volume 107, Number 9

Siderophore-mediated iron transport: crystal structure of FhuA with bound lipopolysaccharide.

Abstract: FhuA, the receptor for ferrichrome-iron in Escherichia coli, is a member of a family of integral outer membrane proteins, which, together with the energy-transducing protein TonB, mediate the active transport of ferric siderophores across the outer membrane of Gram-negative bacteria. The three-dimensional structure of FhuA is presented here in two conformations: with and without ferrichrome-iron at resolutions of 2.7 and 2.5 angstroms, respectively. FhuA is a β barrel composed of 22 antiparallel β strands. In contrast to the typical trimeric arrangement found in porins, FhuA is monomeric. Located within the β barrel is a structurally distinct domain, the “cork,” which mainly consists of a four-stranded β sheet and four short α helices. A single lipopolysaccharide molecule is noncovalently associated with the membrane-embedded region of the protein. Upon binding of ferrichrome-iron, conformational changes are transduced to the periplasmic pocket of FhuA, signaling the ligand-loaded status of the receptor. Sequence homologies and mutagenesis data are used to propose a structural mechanism for TonB-dependent siderophore-mediated transport across the outer membrane.