Rapid Decline of a Grassland System and Its Ecological and Conservation Implications

One of the most important conservation issues in ecology is the imperiled state of grassland ecosystems worldwide due to land conversion, desertification, and the loss of native populations and species. The Janos region of northwestern Mexico maintains one of the largest remaining black-tailed prairie dog (Cynomys ludovicianus) colony complexes in North America and supports a high diversity of threatened and endangered species. Yet, cattle grazing, agriculture, and drought have greatly impacted the region. We evaluated the impact of human activities on the Janos grasslands, comparing changes in the vertebrate community over the last two decades. Our results reveal profound, rapid changes in the Janos grassland community, demonstrating large declines in vertebrate abundance across all taxonomic groups. We also found that the 55,000 ha prairie dog colony complex has declined by 73% since 1988. The prairie dog complex has become increasingly fragmented, and their densities have shown a precipitous decline over the years, from an average density of 25 per ha in 1988 to 2 per ha in 2004. We demonstrated that prairie dogs strongly suppressed woody plant encroachment as well as created open grassland habitat by clearing woody vegetation, and found rapid invasion of shrubland once the prairie dogs disappeared from the grasslands. Comparison of grasslands and shrublands showed markedly different species compositions, with species richness being greatest when both habitats were considered together. Our data demonstrate the rapid decline of a grassland ecosystem, and documents the dramatic loss in biodiversity over a very short time period concomitant with anthropogenic grassland degradation and the decline of a keystone species.     

Coordination network solids based on Cu(II) coordination compounds with 1,4-bis-(1,2,4-triazol-1-yl)-butane as a flexible alkyl spacer ligand: Synthesis, characterization and X-ray structures

The coordination chemistry of three selected copper(II) salts with the flexible ligand 1,4-bis(1,2,4-triazol-1-yl)butane (abbreviated as btb) is described. This ligand acts as a bidentate ligand, bridging copper(II) ions, thereby generating polymers in 2D and 3D network solids.     

Flexibility in crosstalk between H2B ubiquitination and H3 methylation in vivo

Histone H2B ubiquitination is a dynamic modification that promotes methylation of histone H3K79 and H3K4. This crosstalk is important for the DNA damage response and has been implicated in cancer. Here, we show that in engineered yeast strains, ubiquitins tethered to every nucleosome promote H3K79 and H3K4 methylation from a proximal as well as a more distal site, but only if in a correct orientation. This plasticity indicates that the exact location of the attachment site, the native ubiquitin-lysine linkage and ubiquitination cycles are not critical for trans-histone crosstalk in vivo. The flexibility in crosstalk also indicates that other ubiquitination events may promote H3 methylation.     

The interaction of ammonia and xenon with the imidazole glycerol phosphate synthase from Thermotoga maritima as detected by NMR spectroscopy

The imidazole glycerol phosphate (ImGP) synthase from the hyperthermophilic bacterium Thermotoga maritima is a 1:1 complex of the glutaminase subunit HisH and the cyclase subunit HisF. It has been proposed that ammonia generated by HisH is transported through a channel to the active site of HisF, which generates intermediates of histidine (ImGP) and de novo biosynthesis of 5‐aminoimidazole‐4‐carboxamideribotide. Solution NMR spectroscopy of ammonium chloride‐titrated samples was used to study the interaction of NH₃ with amino acids inside this channel. Although numerous residues showed ¹⁵N chemical shift changes, most of these changes were caused by nonspecific ionic strength effects. However, several interactions appeared to be specific. Remarkably, the amino acid residue Thr 78—which is located in the central channel—shows a large chemical shift change upon titration with ammonium chloride. This result and the reduced catalytic activity of the Thr78Met mutant indicate a special role of this residue in ammonia channeling. To detect and further characterize internal cavities in HisF, which might for example contribute to ammonia channeling, the interaction of HisF with the noble gas xenon was analyzed by solution NMR spectroscopy using ¹H‐¹⁵N HSQC experiments. The results indicate that HisF contains three distinct internal cavities, which could be identified by xenon‐induced chemical shift changes of the neighboring amino acid residues. Two of these cavities are located at the active site at opposite ends of the substrate N′‐[(5′‐phosphoribulosyl)formimino]‐5‐aminoimidazole‐4‐carboxamide‐ribonucleotide (PRFAR) binding groove. The third cavity is located in the interior of the central β‐barrel of HisF and overlaps with the putative ammonia transport channel.     

Biodistribution studies with tumor-targeting bispecific antibodies reveal selective accumulation at the tumor site

Bispecific antibodies are proteins that bind two different antigens and may retarget immune cells with a binding moiety specific for a leukocyte marker. A binding event in blood could in principle prevent antibody extravasation and accumulation at the site of disease. In this study, we produced and characterized two tetravalent bispecific antibodies that bind with high affinity to the alternatively-spliced EDB domain of fibronectin, a tumor-associated antigen. The bispecific antibodies simultaneously engaged the cognate antigens (murine T cell co-receptor CD3 and hen egg lysozyme) and selectively accumulated on murine tumors in vivo. The results, which were in agreement with predictions based on pharmacokinetic modeling and antibody binding characteristics, confirmed that bispecific antibodies can reach abluminal targets without being blocked by peripheral blood leukocytes.     

How Molecules with Dipole Moments Enhance the Selectivity of Electrodes in Organic Solar Cells – A Combined Experimental and Theoretical Approach

Simple organic molecules with permanent dipole moments – amino acids and heterocycles – have been successfully employed in bulk‐heterojunction organic solar cells as interlayer between photoactive material and electron contact. A large increase of open‐circuit voltage and fill factor can be observed for four different polymers as donor material in the photoactive layer. A combination of current–voltage curves, scanning Kelvin‐probe atomic force microscopy, ultraviolet photoelectron spectroscopy, and electroluminescence measurements as well as numerical simulations are carried out to clarify in detail the underlying mechanisms. All results fully confirm the hypothesis that the main effect is an accumulation of electrons and a depletion of holes in the photoactive layer in the vicinity of the electron contact induced by a decrease of its effective work function. Further, density functional theory calculations and literature reports of the energy levels of the dipole molecules strongly suggest that the charge carriers tunnel through the thin dipole layer which does however not limit the current. This represents a versatile, simple, and cheap method to realize highly selective contacts which may also be beneficial for other types of solar cells and devices where contact selectivity is crucial.