The many blades of the β-propeller proteins: conserved but versatile

The β-propeller is a highly symmetrical structure with 4-10 repeats of a four-stranded antiparallel β-sheet motif. Although β-propeller proteins with different blade numbers all adopt disc-like shapes, they are involved in a diverse set of functions, and defects in this family of proteins have been associated with human diseases. However, it has remained ambiguous how variations in blade number could alter the function of β-propellers. In addition to the regularly arranged β-propeller topology, a recently discovered β-pinwheel propeller has been found. Here, we review the structural and functional diversity of β-propeller proteins, including β-pinwheels, as well as recent advances in the typical and atypical propeller structures.     

Strong but opposing β-diversity–stability relationships in coral reef fish communities

The ‘diversity–stability hypothesis’, in which higher species diversity within biological communities buffers the risk of ecological collapse, is now generally accepted. However, empirical evidence for a relationship between β-diversity (spatial turnover in community structure) and temporal stability in community structure remains equivocal, despite important implications for theoretical ecology and conservation biology. Here, we report strong β-diversity–stability relationships across a broad sample of fish taxa on Australia''s Great Barrier Reef. These relationships were robust to random sampling error and spatial and environmental factors, such as latitude, reef size and isolation. While β-diversity was positively associated with temporal stability at the community level, the relationship was negative for some taxa, for example surgeonfishes (Acanthuridae), one of the most abundant reef fish families. This demonstrates that the β-diversity–stability relationship should not be indiscriminately assumed for all taxa, but that a species’ risk of extirpation in response to disturbance is likely to be taxon specific and trait based. By combining predictions of spatial and temporal turnover across the study area with observations in marine-protected areas, we conclude that protection alone does not necessarily confer temporal stability and that taxon-specific considerations will improve the outcome of conservation efforts.     

A conformational constraint improves a β-secretase inhibitor but for an unexpected reason

During our ongoing efforts to develop a small molecule inhibitor targeting the β-amyloid cleaving enzyme (BACE-1), we discovered a class of compounds bearing an aminoimidazole motif. Initial optimization led to potent compounds that have high Pgp efflux ratios. Crystal structure-aided design furnished conformationally constrained compounds that are both potent and have relatively low Pgp efflux ratios. Computational studies performed after these optimizations suggest that the introduction of the constraint enhances potency via additional hydrophobic interactions rather than conformational restriction.     

Testis-specific β2 tubulins are identical in Drosophila melanogaster and D. hydei but differ from the ubiquitous β1 tubulin

In Drosophila as in many organisms tubulins are encoded by a gene family. We have determined the complete nucleotide sequences coding for the 1 and 2 tubulins of Drosophila melanogaster and the 2 tubulin of D. hydei, and found these insect tubulins to be highly conserved and like tubulins of other organisms. This is discussed with reference to the possible functional domains of these proteins. — The 1 tubulin gene of Drosophila is constitutively expressed, whereas the 2 tubulin is expressed specifically in the testes. In D. melanogaster the amino acid sequences of these proteins are 95% homologous, differing at only 25 positions. In the testes the 2 tubulin participates in different microtubules as shown by genetic analysis (Kemphues et al. 1982). Interestingly, all of the amino acids characteristic of the testis-specific 2 tubulin are also present in the corresponding gene of D. hydei. Of special interest is the high degree of conservation of the carboxy-terminal domain in these functionally equivalent tubulins.     

Starch-accumulating Sweet Potato Callus Tissue Devoid of β-Amylase but with Two Starch Phosphorylase Isozymes

By controlling the concentrations of kinetin, auxin, and sucrose in the Murashige–Skoog medium, starch contents in callus culture induced from sweet potato tissues could be manipulated. Activity staining and Western analysis on PAGE plates and activity assays made on starch phosphorylase in the presence and absence of mercuric ions showed that β-amylase is absent in callus cultures regardless of whether their starch content is high or low. This would imply that β-amylase induction in sweet potato calli is not linked to the metabolic control through which the expression of storage function is associated, as proposed by Nakamura et al. [Plant Physiol., 96, 902 (1991)] for sweet potato leaf-petiole cuttings. Analyses of starch phosphorylase in crude extracts suggested the presence of a new starch phosphorylase in tuberous root and callus tissue. This phosphorylase is immunologically different from the tuberous root and leaf enzymes that we studied previously.     

ACKR3 Regulation of Neuronal Migration Requires ACKR3 Phosphorylation,but Not β-Arrestin

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Nitration of β-Lactoglobulin but Not of Ovomucoid Enhances Anaphylactic Responses in Food Allergic Mice

BackgroundWe revealed in previous studies that nitration of food proteins reduces the risk of de novo sensitization in a murine food allergy model. In contrast, in situations with preformed specific IgE antibodies, in vitro experiments suggested an increased capacity of effector cell activation by nitrated food proteins.ObjectiveThe aim of this study was to investigate the influence of protein nitration on the effector phase of food allergy.DesignBALB/c mice were immunized intraperitoneally (i.p.) with the milk allergen β-lactoglobulin (BLG) or the egg allergen ovomucoid (OVM), followed by intragastric (i.g.) gavages to induce a strong local inflammatory response and allergen-specific antibodies. Subsequently, naïve and allergic mice were intravenously (i.v.) challenged with untreated, sham-nitrated or nitrated BLG or OVM. Anaphylaxis was monitored by measuring core body temperature and determination of mouse mast cell protease-1 (mMCP-1) levels in blood.ResultsA significant drop of body temperature accompanied with significantly elevated concentrations of the anaphylaxis marker mMCP-1 were only observed in BLG allergic animals challenged with nitrated BLG and not in OVM allergic mice challenged with nitrated OVM. SDS-PAGE and circular dichroism analysis of the differentially modified allergens revealed an effect of nitration on the secondary protein structure exclusively for BLG together with enhanced protein aggregation.ConclusionOur data suggest that nitration affects differently the food allergens BLG and OVM. In the case of BLG, structural changes favored dimerization possibly explaining the increased anaphylactic reactivity in BLG allergic animals.     

Mutation of tyrosine residue 857 in the PDGF β-receptor affects cell proliferation but not migration

Activation of platelet-derived growth factor (PDGF) receptors occurs through ligand-induced dimerization and autophosphorylation. In this study, we investigated the effects of mutation of tyrosine residue 857 (Y857) in the activation loop of the PDGF β-receptor (PDGFRβ) to phenylalanine (Y857F). In agreement with previous observations, we found that PDGFRβ^Y857F had a severely diminished in vitro kinase activity. However, in vivo the overall amount of tyrosine phosphorylation of PDGFRβ^Y857F was similar to that of the wild-type receptor, except for the tyrosine residue 771 (Y771) which displayed a stronger phosphorylation in the mutant receptor. Analysis of the ability to induce signal transduction revealed that the PDGFRβ^Y857F mutant had an attenuated activation of Akt and Erk1/2 MAP kinase. In contrast, the mutant receptor efficiently mediated phosphorylation of the ubiquitin-ligase c-Cbl that participates in receptor internalization and degradation, and PLCγ which has previously been shown to be connected with various cellular responses, including migration. However, the protein tyrosine phosphatase SHP-2, implicated in the PDGF-induced mitogenic response, together with the adaptor proteins Alix and Stam, involved in intracellular sorting of receptor, was not phosphorylated in cells expressing PDGFRβ^Y857F. We found that both receptor variants were internalized from the cell surface and degraded at a comparable rate. Interestingly, PDGFRβ^Y857F was unable to mediate PDGF-BB-induced mitogenic signaling, whereas it could elicit a chemotactic response.     

Pancreatic β-Cell Death due to Pdx-1 Deficiency Requires Multi-BH Domain Protein Bax but Not Bak

Diabetes develops in Pdx1-haploinsufficient mice due to an increase in β-cell death leading to reduced β-cell mass and decreased insulin secretion. Knockdown of Pdx1 gene expression in mouse MIN6 insulinoma cells induced apoptotic cell death with an increase in Bax activation and knockdown of Bax reduced apoptotic β-cell death. In Pdx1 haploinsufficient mice, Bax ablation in β-cells increased β-cell mass, decreased the number of TUNEL positive cells and improved glucose tolerance after glucose challenge. These changes were not observed with Bak ablation in Pdx1-haploinsufficient mice. These results suggest that Bax mediates β-cell apoptosis in Pdx1-deficient diabetes.     

TGF β-induced cartilage repair is maintained but fibrosis is blocked in the presence of Smad7

Cartilage damage in osteoarthritis (OA) is considered an imbalance between catabolic and anabolic factors, favoring the catabolic side. We assessed whether adenoviral overexpression of transforming growth factor-β (TGFβ) enhanced cartilage repair and whether TGFβ-induced fibrosis was blocked by local expression of the intracellular TGFβ inhibitor Smad7. We inflicted cartilage damage by injection of interleukin-1 (IL-1) into murine knee joints. After 2 days, we injected an adenovirus encoding TGFβ. On day 4, we measured proteoglycan (PG) synthesis and content. To examine whether we could block TGFβ-induced fibrosis and stimulate cartilage repair simultaneously, we injected Ad-TGFβ and Ad-Smad7. This was performed both after IL-1-induced damage and in a model of primary OA. In addition to PG in cartilage, synovial fibrosis was measured by determining the synovial width and the number of procollagen I-expressing cells. Adenoviral overexpression of TGFβ restored the IL-1-induced reduction in PG content and increased PG synthesis. TGFβ-induced an elevation in PG content in cartilage of the OA model. TGFβ-induced synovial fibrosis was strongly diminished by simultaneous synovial overexpression of Smad7 in the synovial lining. Of great interest, overexpression of Smad7 did not reduce the repair-stimulating effect of TGFβ on cartilage. Adenoviral overexpression of TGFβ stimulated repair of IL-1- and OA-damaged cartilage. TGFβ-induced synovial fibrosis was blocked by locally inhibiting TGFβ signaling in the synovial lining by simultaneously transfecting it with an adenovirus overexpressing Smad7.     

Mitochondrial,but not peroxisomal, β-oxidation of fatty acids is conserved in coenzyme A-Deficient rat liver

Growth hormone (GH) exerts acute insulin-like effects, such as increased lipogenesis and inhibition of catecholamine-induced lipolysis, in rat adipocytes that have not been exposed to GH during the preceding three hours. We found that OPC3911, a highly specific inhibitor of the cGMP-inhibited cAMP phosphodiesterase, completely blocked the antilipolytic but not the lipogenic effect of GH. This indicates that the antilipolytic effect of GH is mediated through activation of this phosphodiesterase leading to reduction of cAMP levels in the same manner as has been shown for insulin.     

Biocontrol-risky but necessary?

There is currently much debate concerning the risks of biological control and the potential harmful effects of nonindigenous species introduced for controlling exotic pests. Biocontrol advocates generally appear reluctant to accept the possibility that there could be side-effects associated with biocontrol, often refuting evidence of harmful effects and suggesting that current practices are sufficient to minimize any risks. The biocontrol critics, on the other hand, although eager to provide evidence to the contrary, appear reluctant to propose any detailed, constructive criticisms or workable solutions. Here, we attempt to put these arguments into context, and suggest some directions for future research that might help to resolve some of the problems.     

Spinal δ2 but not δ1 opioid receptors are involved in intracereboventricular β-endorphin-induced antinociception in the mouse

The antinociception induced by β-endorphin given intracerebroventricularly (i.c.v.) has been previously demonstrated to be mediated by the release of Met-enkephalin and subsequent stimulation of δ receptors in the spinal cord for antinociception. The present study was designed to determine what type of opioid receptor, δ1 or δ2, in the spinal cord is involved in i.c.v. β-endorphin-induced antinociception. Antinociception was assessed by the tail-flick test in male ICR mice. NTB (0.2–20 nmol) and NTI0 (0.22–2.2 nmol),selective δ2 receptor antagonists, given intrathecally (i.t.) dose-dependently attenuated i.c.v. β-endorphin-induced inhibition of the tail-flick response. On the other hand, BNTX (0.02–2.2 nmol), a selective δ1 receptor antagonist, given i.t., did not block i.c.v. β-endorphin-induced antinociception. The tail-flick inhibition induced by DAMGO, a μ receptor agonist, or U50,488H, a к receptor agonist, was not blocked by i.t. BNTX, NTB or NTI. It is concluded that δ2 but not δ1 receptors in the spinal cord are involved in i.c.v. β-endorphin-induced antinociception.     

NO donor induces Nec-1-inhibitable, but RIP1-independent, necrotic cell death in pancreatic β-cells

Nitric oxide (NO) has been implicated in pancreatic β-cell death in the development of diabetes. The mechanisms underlying NO-induced β-cell death have not been clearly defined. Recently, receptor-interacting protein-1 (RIP1)-dependent necrosis, which is inhibited by necrostatin-1, an inhibitor of RIP1, has emerged as a form of regulated necrosis. Here, we show that NO donor-induced β-cell death was inhibited by necrostatin-1. Unexpectedly, however, RIP1 knockdown neither inhibited cell death nor altered the protective effects of necrostatin-1 in NO donor-treated β-cells. These results indicate that NO donor induces necrostatin-1-inhibitable necrotic β-cell death independent of RIP1. Our findings raise the possibility that NO-mediated β-cell necrosis may be a novel form of signal-regulated necrosis, which play a role in the progression of diabetes.     

The increase in rat ventricular automaticity induced by salbutamol is mediated through β(1)- but not β(2)-adrenoceptors: role of phosphodiesterases

AimsWhile β₂-adrenoceptor (AR) agonists are useful bronchodilators, they also produce cardiac arrhythmias. These agents are not fully selective and also activate β₁-AR, but the involvement of β₁-AR and β₂-AR in the observed pro-arrhythmic effect has not been established. We studied the effect of β₁-AR and β₂-AR activation on ventricular automaticity and the role of phosphodiesterases (PDE) in regulating this effect.Main methodsExperiments were performed in the spontaneously beating isolated right ventricle of the rat heart. We also measured cAMP production in this tissue.Key findingsThe β₂-AR agonist salbutamol (1-100 μM) produced a concentration-dependent increase in ventricular automaticity that was not affected by 50 nM of the β₂-AR antagonist ICI 118551. This effect was enhanced by the non-selective PDE inhibitor theophylline (100 μM) and by the selective PDE4 inhibitors rolipram (1 μM) and Ro 201724 (2 μM), but not modified by the selective PDE3 inhibitors cilostamide (0.3 μM) or milrinone (0.2 μM). The effects of salbutamol alone and in the presence of either theophylline or rolipram were virtually abolished by 0.1 μM β₁-AR antagonist CGP20712A. Salbutamol (10 μM) increased the cAMP concentration, and this effect was abolished by CGP 20712A (0.1 μM) but enhanced by theophylline (100 μM) or rolipram (1 μM). Cilostamide (0.3 μM) failed to modify the effect of salbutamol on cAMP concentration.SignificanceThese results indicate that the increase of ventricular automaticity elicited by salbutamol was exclusively mediated through β₁-AR and enhanced by non-selective PDE inhibition with theophylline or selective PDE4 inhibition. However, PDE3 did not appear to regulate this effect.     

Chronic β2 adrenergic agonist, but not exercise, improves glucose handling in older type 2 diabetic mice

Insulin resistant type 2 diabetes mellitus in the obese elderly has become a worldwide epidemic. While exercise can prevent the onset of diabetes in young subjects its role in older diabetic people is less clear. Exercise stimulates the release of the β(2)-agonist epinephrine more in the young. Although epinephrine and β(2)-agonist drugs cause acute insulin resistance, their chronic effect on insulin sensitivity is unclear. We fed C57BL/6 mice a high fat diet to induce diabetes. These overweight animals became very insulin resistant. Exhaustive treadmill exercise 5 days a week for 8 weeks had no effect on their diabetes, nor did the β(2)-blocking drug ICI 118551. In contrast, exercise combined with the β(2)-agonist salbutamol (albuterol) had a beneficial effect on both glucose tolerance and insulin sensitivity after 4 and 8 weeks of exercise. The effect was durable and persisted 5 weeks after exercise and β(2)-agonist had stopped. To test whether β(2)-agonist alone was effective, the animals that had received β(2)-blockade were then given β(2)-agonist. Their response to a glucose challenge improved but their response to insulin was not significantly altered. The β(2)-agonists are commonly used to treat asthma and asthmatics have an increased incidence of obesity and type 2 diabetes. Although β(2)-agonists cause acute hyperglycemia, chronic treatment improves insulin sensitivity, probably by improving muscle glucose uptake.