Glycine reduces platelet aggregation

It has been demonstrated that a wide variety of white blood cells and macrophages (i.e. Kupffer cells, alveolar and peritoneal macrophages and neutrophils) contain glycine-gated chloride channels. Binding of glycine on the receptor stimulates Cl^? influx causing membrane hyperpolarization that prevents agonist-induced influx of calcium. Since platelet-aggregation is calcium-dependent, this study was designed to test the hypothesis that glycine would inhibit platelet aggregation. Rats were fed diets rich of glycine for 5 days, while controls received isonitrogenous valine. The bleeding time and ADP- and collagen-induced platelet aggregation were measured. Dietary glycine significantly increased bleeding time about twofold compared to valine-treated controls. Furthermore, the amplitude of platelet aggregation stimulated with ADP or collagen was significantly decreased in whole blood drawn from rats fed 2.5 or 5 % dietary glycine by over 50 %. Addition of glycine in vitro (1–10 mM) also blunted rat platelet aggregation in a dose-dependent manner. Strychnine, a glycine receptor antagonist, abrogated the inhibitory effect of glycine on platelet-aggregation in vitro suggesting the glycine works via a glycine receptor. Glycine also blunted aggregation of human platelets. Further, the glycine receptor was detected in both rat and human platelets by western blotting. Based on these data, it is concluded that glycine prevents aggregation of platelets in a dose-dependent manner via mechanisms involving a glycine receptor.     

Decoding the ‘zeep’ complex: quantitative analysis of interspecific variation in the nocturnal flight calls of nine wood warbler species (Parulidae spp.)

ABSTRACT

The “zeep” complex consists of nine birds that produce nocturnal flight calls with similar acoustic features. Our inability to distinguish these calls inhibits the acoustic monitoring of these species. We test the hypothesis that flight calls of nine warblers in the “zeep” complex show sufficient acoustic differences to allow differentiation. We investigate divergence in these vocalizations by recording birds held for banding and collecting additional recordings from sound libraries. We used three approaches to compare calls between species: analysis of variance in acoustic properties, discriminant analysis of acoustic properties, and spectrographic cross-correlation. The first approach revealed five species that were different in one or more acoustic properties. The second approach revealed a level of assignment to the correct species (73%) that exceeded levels expected by chance (36%). The third approach revealed calls of seven species to be significantly more similar to conspecific calls than heterospecific calls. Our results suggest the calls of many members of the “zeep” complex exhibit species-specific differences in structure, which may allow differentiation of at least five “zeep” species based on call alone. We advocate for the combined use of these three approaches for the comparison of “zeep” calls in future flight call studies.     

Improved heterologous production of the nonribosomal peptide‐polyketide siderophore yersiniabactin through metabolic engineering and induction optimization

Biosynthesis of complex natural products like polyketides and nonribosomal peptides using Escherichia coli as a heterologous host provides an opportunity to access these molecules. The value in doing so stems from the fact that many compounds hold some therapeutic or other beneficial property and their original production hosts are intractable for a variety of reasons. In this work, metabolic engineering and induction variable optimization were used to increase production of the polyketide‐nonribosomal peptide compound yersiniabactin, a siderophore that has been utilized to selectively remove metals from various solid and aqueous samples. Specifically, several precursor substrate support pathways were altered through gene expression and exogenous supplementation in order to boost production of the final compound. The gene expression induction process was also analyzed to identify the temperatures and inducer concentrations resulting in highest final production levels. When combined, yersiniabactin production was extended to ～175 mg L^?1. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1412–1417, 2016     

The biomechanics of concussion for ice hockey head impact events

The purpose of this research was to conduct reconstructions of concussive and non-concussive impacts in ice hockey to determine the biomechanics and thresholds of concussive injury in ice hockey. Videos of concussive and non-concussive impacts in an elite professional ice hockey league in North America were reconstructed using physical and finite element model methods. Eighty concussive and 45 non-concussive events were studied. Logistic regressions indicate significant thresholds for concussion for linear/rotational acceleration and CSDM_10%. Impacts in ice hockey were mostly long duration events, longer than 15?ms. These results have significant implications for helmet standards and development to prevent concussion.     

Role of Ser216 in the mechanism of action of membrane-bound lytic transglycosylase B: further evidence for substrate-assisted catalysis

Lytic transglycosylases cleave the beta-(1-->4)-glycosidic bond in the bacterial cell wall heteropolymer peptidoglycan between the N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) residues with the concomitant formation of a 1,6-anhydromuramoyl residue. Based on sequence alignments, Ser216 in Pseudomonas aeruginosa membrane-bound lytic transglycosylase B (MltB) was targeted for replacement with alanine to delineate its role in the enzyme's mechanism of action. The specific activity of the Ser216-->Ala MltB derivative was less than 12% of that for the wild-type enzyme, while its substrate binding affinity remained virtually unaltered. These data are in agreement with a role of Ser216 in orienting the N-acetyl group on MurNAc at the -1 subsite of MltB for its participation in a substrate-assisted mechanism of action.     

Functional role of extranucleosomal DNA and the entry site of the nucleosome in chromatin remodeling by ISW2

A minimal amount of extranucleosomal DNA was required for nucleosome mobilization by ISW2 as shown by using a photochemical histone mapping approach to analyze nucleosome movement on a set of nucleosomes with varied lengths of extranucleosomal DNA. ISW2 was ineffective in repositioning or mobilizing nucleosomes with 相似文献   

Nocardia asteroides culture filtrates cause dopamine depletion and cytotoxicity in PC12 cells

Experimental infection of BALB/c mice with the gram-positive bacterium Nocardia asteroides produces marked loss of nigrostriatal dopamine neurons, resulting in striatal dopamine depletion. To investigate the mechanism(s) responsible for this neuronal loss, we evaluated the influence of N. asteroides cell-free culture filtrates on rat pheochromocytoma PC12 cells, an in vitro model for dopamine neurons. Changes in cell viability and cell numbers were minimal after 24 h, but increased with longer incubation. In contrast, dopamine depletion occurred after 30 min incubation, and was greater with GUH-2 filtrate than with filtrate from the less virulent strain 10905. Incubation with the culture filtrate decreased viability in neuroblastoma and glioma cell lines, indicating that cytotoxic effects were not limited to dopaminergic cells. These findings suggest that the loss of nigrostriatal dopamine neurons and concomitant striatal dopamine depletion in Nocardia-infected mice may be due, at least in part, to the neurotoxicity of nocardial secretory products.     

Allosteric switching by mutually exclusive folding of protein domains

Many proteins are built from structurally and functionally distinct domains. A major goal is to understand how conformational change transmits information between domains in order to achieve biological activity. A two-domain, bi-functional fusion protein has been designed so that the mechanical stress imposed by the folded structure of one subunit causes the other subunit to unfold, and vice versa. The construct consists of ubiquitin inserted into a surface loop of barnase. The distance between the amino and carboxyl ends of ubiquitin is much greater than the distance between the termini of the barnase loop. This topological constraint causes the two domains to engage in a thermodynamic tug-of-war in which only one can exist in its folded state at any given time. This conformational equilibrium, which is cooperative, reversible, and controllable by ligand binding, serves as a model for the coupled binding and folding mechanism widely used to mediate protein-protein interactions and cellular signaling processes. The position of the equilibrium can be adjusted by temperature or ligand binding and is monitored in vivo by cell death. This design forms the basis for a new class of cytotoxic proteins that can be activated by cell-specific effector molecules, and can thus target particular cell types for destruction.