Disruption of methylarginine metabolism impairs vascular homeostasis

Asymmetric dimethylarginine (ADMA) and monomethyl arginine (L-NMMA) are endogenously produced amino acids that inhibit all three isoforms of nitric oxide synthase (NOS). ADMA accumulates in various disease states, including renal failure, diabetes and pulmonary hypertension, and its concentration in plasma is strongly predictive of premature cardiovascular disease and death. Both L-NMMA and ADMA are eliminated largely through active metabolism by dimethylarginine dimethylaminohydrolase (DDAH) and thus DDAH dysfunction may be a crucial unifying feature of increased cardiovascular risk. However, despite considerable interest in this pathway and in the role of ADMA as a cardiovascular risk factor, there is little evidence to support a causal role of ADMA in pathophysiology. Here we reveal the structure of human DDAH-1 and probe the function of DDAH-1 both by deleting the DDAH1 gene in mice and by using DDAH-specific inhibitors which, as we demonstrate by crystallography, bind to the active site of human DDAH-1. We show that loss of DDAH-1 activity leads to accumulation of ADMA and reduction in NO signaling. This in turn causes vascular pathophysiology, including endothelial dysfunction, increased systemic vascular resistance and elevated systemic and pulmonary blood pressure. Our results also suggest that DDAH inhibition could be harnessed therapeutically to reduce the vascular collapse associated with sepsis.     

A single layer of microtubules is part of a complex cytoskeleton in mature nematocytes of hydra

The architecture of microtubules in mature nematocytes (stinging cells) of Hydra attenuata was investigated in detail by an indirect immunofluorescence study and by scanning and transmission electron microscopy in order to comprehend the function of the cytoskeleton in this extremely complex cell type. Microtubules were detected in all types of nematocytes in the tentacles and were found to be arranged in parallel arrays forming a highly organized basket-like structure around the nematocysts.     

Left handed �� helix models for mammalian prion fibrils

We propose models for in vitro grown mammalian prion protein fibrils based upon left handed beta helices formed both from the N-terminal and C-terminal regions of the proteinase resistant infectious prion core. The C-terminal threading onto a β-helical structure is almost uniquely determined by fixing the cysteine disulfide bond on a helix corner. In comparison to known left handed helical peptides, the resulting model structures have similar stability attributes including relatively low root mean square deviations in all atom molecular dynamics, substantial side-chain-to-side-chain hydrogen bonding, good volume packing fraction, and low hydrophilic/hydrophobic frustration. For the N-terminus, we propose a new threading of slightly more than two turns, which improves upon the above characteristics relative to existing three turn β-helical models. The N-terminal and C-terminal beta helices can be assembled into eight candidate models for the fibril repeat units, held together by large hinge (order 30 residues) domain swapping, with three amenable to fibril promoting domain swapping via a small (five residue) hinge on the N-terminal side. Small concentrations of the metastable C-terminal β helix in vivo might play a significant role in templating the infectious conformation and in enhancing conversion kinetics for inherited forms of the disease and explain resistance (for canines) involving hypothesized coupling to the methionine 129 sulfur known to play a role in human disease.Key words: prion, amyloid fibril, domain swap, beta helix, computational biology     

transAlign: using amino acids to facilitate the multiple alignment of protein-coding DNA sequences

Background  

Alignments of homologous DNA sequences are crucial for comparative genomics and phylogenetic analysis. However, multiple alignment represents a computationally difficult problem. For protein-coding DNA sequences, it is more advantageous in terms of both speed and accuracy to align the amino-acid sequences specified by the DNA sequences rather than the DNA sequences themselves. Many implementations making use of this concept of "translated alignments" are incomplete in the sense that they require the user to manually translate the DNA sequences and to perform the amino-acid alignment. As such, they are not well suited to large-scale automated alignments of large and/or numerous DNA data sets.     

Neuregulin 3 promotes excitatory synapse formation on hippocampal interneurons

Hippocampal GABAergic interneurons are crucial for cortical network function and have been implicated in psychiatric disorders. We show here that Neuregulin 3 (Nrg3), a relatively little investigated low‐affinity ligand, is a functionally dominant interaction partner of ErbB4 in parvalbumin‐positive (PV) interneurons. Nrg3 and ErbB4 are located pre‐ and postsynaptically, respectively, in excitatory synapses on PV interneurons in vivo. Additionally, we show that ablation of Nrg3 results in a similar phenotype as the one described for ErbB4 ablation, including reduced excitatory synapse numbers on PV interneurons, altered short‐term plasticity, and disinhibition of the hippocampal network. In culture, presynaptic Nrg3 increases excitatory synapse numbers on ErbB4⁺ interneurons and affects short‐term plasticity. Nrg3 mutant neurons are poor donors of presynaptic terminals in the presence of competing neurons that produce recombinant Nrg3, and this bias requires postsynaptic ErbB4 but not ErbB4 kinase activity. Furthermore, when presented by non‐neuronal cells, Nrg3 induces postsynaptic membrane specialization. Our data indicate that Nrg3 provides adhesive cues that facilitate excitatory neurons to synapse onto ErbB4⁺ interneurons.     

Heat dissociation and maceration of marine Cnidaria

Summary The effect of increased temperature on the tissue integrity of polyps and medusae ofPodocoryne carnea is described. Animals exposed for 10 to 20 min to a temperature of 35°C are easily dissociated into single cells. These dissociated cells round up, form reaggregates and, depending on their origin, regenerate polyp or medusa structures. However, as the exposure time is increased, the dissociated cells gradually lose the ability to reaggregate or to regenerate defined structures. At incubation times exceeding 50 min, the tissue separates into single cells which retain their normalin vivo shapes but which do not form reaggregates. These are termed macerated cells. The ultrastructure and protein profile of macerated cells demonstrate no major changes from those of untreated cells. Both the dissociation and maceration methods are applicable to other cnidarian species for developmental, histological and biochemical studies.