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 & Visualization. The organization has 12115 authors who have published 27401 publications receiving 951162 citations. The organization is also known as: University of Constance & Universität Konstanz.

Identification and characterization of a new conserved motif within the presequence of proteins targeted into complex diatom plastids

Abstract: Several groups of algae evolved by secondary endocytobiosis, which is defined as the uptake of a eukaryotic alga into a eukaryotic host cell and the subsequent transformation of the endosymbiont into an organelle. Due to this explicit evolutionary history such algae possess plastids that are surrounded by either three or four membranes. Protein targeting into plastids of these organisms depends on N-terminal bipartite presequences consisting of a signal and a transit peptide domain. This suggests that different protein targeting systems may have been combined during establishment of secondary endocytobiosis to enable the transport of proteins into the plastids. Here we demonstrate the presence of an apparently new type of transport into diatom plastids. We analyzed protein targeting into the plastids of diatoms and identified a conserved amino acid sequence motif within plastid preprotein targeting sequences. We expressed several diatom plastid presequence:GFP fusion proteins with or without modifications within that motif in the diatom Phaeodactylum tricornutum and found that a single conserved phenylalanine is crucial for protein transport into the diatom plastids in vivo, thus indicating the presence of a so far unknown new type of targeting signal. We also provide experimental data about the minimal requirements of a diatom plastid targeting presequence and demonstrate that the signal peptides of plastid preproteins and of endoplasmic reticulum-targeted preproteins in diatoms are functionally equivalent. Furthermore we show that treatment of the cells with Brefeldin A arrests protein transport into the diatom plastids suggesting that a vesicular transport step within the plastid membranes may occur.

Nitrous oxide reductase from denitrifying Pseudomonas perfectomarina. Purification and properties of a novel multicopper enzyme.

Abstract: Nitrous oxide reductase from the denitrifying bacterium Pseudomonas perfectomarina has been isolated and purified to homogeneity The enzyme contained about eight copper atoms/120 kDa and was composed of two presumably identical subunits The isoelectric point was 51 Several spectroscopically distinct forms of the enzyme were identified A 'pink' form of the enzyme was obtained when the purification was done aerobically The specific activity of this species was around 30 nkat/mg protein as measured by the nitrous-oxide-dependent oxidation of photochemically reduced benzyl viologen A 'purple' form of the enzyme, whose catalytic activity was 2-5-fold higher, was obtained when the purification was done anaerobically The activity of both forms of the enzyme was substantially increased by dialyzing the protein against 2-(N-cyclohexylamino)ethanesulfonate buffer at pH approximately equal to 10 A maximal activity of 1000 nkat/mg protein has been obtained for the purple form using this procedure A 'blue', enzymatically inactive form of the enzyme resulted when either the pink or the purple species was exposed to excess dithionite or ascorbate Anaerobic, potentiometric titrations of both the purple and the pink form of the enzyme gave a Nernst factor, n540, of 095 and a midpoint potential, E'0,540 of +260 mV (vs SHE, 25 degrees C, Tris/HCl buffer, pH 75) Electron paramagnetic resonance (EPR) and optical spectra of N2O reductase suggested the presence of an unusual type 1 copper center Type 2 copper was absent The hyperfine splitting in the g parallel region consisted of a seven-line pattern In the presence of excess of reductant, a broad EPR signal with g values at 218 and 206 was observed The EPR spectra of the pink and purple forms of the enzyme were similar; however, the spectrum of the purple form was better resolved with g parallel = 218 (A parallel = 383 mT) and g perpendicular = 203 (A perpendicular = 28 mT) Most of the copper in N2O reductase was removed by anaerobic dialysis against KCN Reaction of the apoprotein with Cu(en)2SO4 partially regenerated the optical and EPR spectra of the holoprotein; the resulting protein was enzymatically inactive Monospecific antibodies against the copper protein strongly inhibited the N2O reductase activity of purified samples and cell-free extracts

ICDAR 2013 Table Competition

Abstract: Table understanding is a well studied problem in document analysis, and many academic and commercial approaches have been developed to recognize tables in several document formats, including plain text, scanned page images and born-digital, object-based formats such as PDF. Despite the abundance of these techniques, an objective comparison of their performance is still missing. The Table Competition held in the context of ICDAR 2013 is our first attempt at objectively evaluating these techniques against each other in a standardized way, across several input formats. The competition independently addresses three problems: (i) table location, (ii) table structure recognition, and (iii) these two tasks combined. We received results from seven academic systems, which we have also compared against four commercial products. This paper presents our findings.

Biogeochemical fluxes through mesozooplankton

Abstract: Mesozooplankton are significant consumers of phytoplankton, and have a significant impact on the oceanic biogeochemical cycles of carbon and other elements. Their contribution to vertical particle flux is much larger than that of microzooplankton, yet most global biogeochemical models have lumped these two plankton functional types together. In this paper we bring together several newly available data syntheses on observed mesozooplankton concentration and the biogeochemical fluxes they mediate, and perform data synthesis on flux rates for which no synthesis was available. We update the equations of a global biogeochemical model with an explicit representation of mesozooplankton (PISCES). We use the rate measurements to constrain the parameters of mesozooplankton, and evaluate the model results with our independent synthesis of mesozooplankton concentration measurements. We also perform a sensitivity study to analyze the impact of uncertainty in the flux rates. The standard model run was parameterized on the basis of the data synthesis of flux rates. The results of mesozooplankton concentration in the standard run are slightly lower than the independent databases of observed mesozooplankton concentrations, but not significantly. This shows that structuring and parameterizing biogeochemical models on the basis of observations without tuning is a strategy that works. The sensitivity study showed that by using a maximum grazing rate of mesozooplankton that is only 30% higher than the poorly constrained fit to the observations, the model mesozooplankton concentration gets closer to the observations, but mesozooplankton grazing becomes higher than what is currently accounted for. This is an indication that food selection by mesozooplankton is not sufficiently quantified at present. Despite the amount of effort that is represented by the data syntheses of all relevant processes, the good results that were obtained for mesozooplankton indicate that this effort needs to be applied to all components of marine biogeochemistry. The development of ecosystem models that better represent key plankton groups and that are more closely based on observations should lead to better understanding and quantification of the feedbacks between marine ecosystems and climate.