Clostridium perfringens Alpha-toxin Recognizes the GM1a-TrkA Complex

Clostridium perfringens alpha-toxin is the major virulence factor in the pathogenesis of gas gangrene. Alpha-toxin is a 43-kDa protein with two structural domains; the N-domain contains the catalytic site and coordinates the divalent metal ions, and the C-domain is a membrane-binding site. The role of the exposed loop region (72–93 residues) in the N-domain, however, has been unclear. Here we show that this loop contains a ganglioside binding motif (H … SXWY … G) that is the same motif seen in botulinum neurotoxin and directly binds to a specific conformation of the ganglioside Neu5Acα2-3(Galβ1-3GalNAcβ1-4)Galβ1-4Glcβ1Cer (GM1a) through a carbohydrate moiety. Confocal microscopy analysis using fluorescently labeled BODIPY-GM1a revealed that the toxin colocalized with GM1a and induced clustering of GM1a on the cell membranes. Alpha-toxin was only slightly toxic in β1,4-N-acetylgalactosaminyltransferase knock-out mice, which lack the a-series gangliosides that contain GM1a, but was highly toxic in α2,8-sialyltransferase knock-out mice, which lack both b-series and c-series gangliosides, similar to the control mice. Moreover, experiments with site-directed mutants indicated that Trp-84 and Tyr-85 in the exposed alpha-toxin loop play an important role in the interaction with GM1a and subsequent activation of TrkA. These results suggest that binding of alpha-toxin to GM1a facilitates the activation of the TrkA receptor and induces a signal transduction cascade that promotes the release of chemokines. Therefore, we conclude that GM1a is the primary cellular receptor for alpha-toxin, which can be a potential target for drug developed against this pathogen.     

Choline Dehydrogenase of Pseudomonas aeruginosa A-16

The promotive effect of biotin (200~500 µg/liter) on l-lysine formation was investigated in Brevibacterium lactofermentum. This effect was observed only when glucose or pyruvate was used as sole carbon source, and accompanied with the specific incorporation of ¹⁸CO₂ into γ-CH₂ group of l-lysine. Brev. lactofermentum AJ 3445 (AEC^r) could grow on pyruvate medium supplemented with biotin at more than 200 µg/liter, while the same growth was observed with the addition of TCA cycle members or glutamate to pyruvate medium.

Phosphoenolpyruvate (PEP) carboxylase deficient mutant derived from AJ 3445 could not grow on glucose as sole carbon source, but on glucose plus 200 µg/liter of biotin. AJ 3445 grown on lactate medium containing 500 µg/liter of biotin and KHCO₃ contained the biotin-dependent pyruvate carboxylase.

These data suggest that this promotive effect of excess biotin on l-lysine formation may be brought about through the activation of pyruvate carboxylase by biotin.     

COPD and disease-specific health status in a working population

Background

It has been debated whether treatment should be started early in subjects with mild to moderate COPD. An impaired health status score was associated with a higher probability of being diagnosed with COPD as compared with undiagnosed COPD.

Purpose

To investigate the health status in a healthy working population, to determine reference scores for healthy non-smoking subjects, and to investigate the relationship between their health status and airflow limitation.

Methods

A total of 1333 healthy industrial workers aged ≥40 years performed spirometry and completed the St. George’s Respiratory Questionnaire (SGRQ) and the COPD Assessment Test (CAT).

Results

The prevalence of COPD defined by the fixed ratio of the forced expiratory volume in one second (FEV₁)/forced vital capacity (FVC) was 10.9%, and the prevalence defined by the Lower Limit of Normal was 5.0%. All SGRQ and CAT scores were skewed to the milder end. In 512 non-smoking subjects with normal spirometry, the mean SGRQ score was 5.7, and the mean CAT score was 5.8. In 145 people with COPD defined by the fixed ratio, the mean SGRQ score was 7.9, with a zero score in 6.9% of the subjects. Using the CAT, the mean score was 7.3, with 7.6% of the scores being zero. The scores in patients identified using the Lower Limit of Normal approach were: SGRQ 8.4 (13.4% had a score of zero) and CAT 7.4 (13.4% had a score of zero). Although the 95th percentiles of the Total, Symptoms, Activity, and Impact scores of the SGRQ and CAT sores were 13.8, 34.0, 23.4, 7.2 and 13.6 in the 512 healthy non-smoking subjects, respectively, they were also distributed under their upper limits in over 80% of the COPD subjects.

Conclusion

The COPD-specific health status scores in a working population were good, even in those with spirometrically diagnosed COPD. All scores were widely distributed in both healthy non-smoking subjects and in subjects with COPD, and the score distribution overlapped remarkably between these two groups. This suggests that symptom-based methods are not suitable screening tools in a healthy general population.     

HA-33 facilitates transport of the serotype D botulinum toxin across a rat intestinal epithelial cell monolayer

A large size botulinum toxin complex (L-TC) is composed of a single neurotoxin (BoNT), a single nontoxic nonhaemagglutinin (NTNHA) and a haemagglutinin (HA) complex. The HA complex is comprised of three HA-70 molecules and three arm structures of HA-33/HA-17 that consist of two HA-33 and a single HA-17. In addition to the mature L-TC, smaller TCs are present in cultures: M-TC (BoNT/NTNHA), M-TC/HA-70 and immature L-TCs with fewer HA-33/HA-17 arms than mature L-TC. Because L-TC displays higher oral toxicity than pure BoNT, it was presumed that nontoxic proteins are critical for food poisoning. In this study, the absorption of TCs across intestinal epithelial cells was assessed by examining the cell binding and monolayer transport of serotype D toxins in the rat intestinal epithelial cell line IEC-6. All TCs, including pure BoNT, displayed binding and transport, with mature L-TC showing the greatest potency. Inhibition experiments using antibodies revealed that BoNT, HA-70 and HA-33 could be responsible for the binding and transport. The findings here indicate that all TCs can transport across the cell layer via a sialic acid-dependent process. Nonetheless, binding and transport markedly increased with number of HA-33/HA-17 arms in the TC. We therefore conclude that the HA-33/HA-17 arm is not necessarily required for, but facilitates, transport of botulinum toxin complexes.     

Impaired insulin signaling in endothelial cells reduces insulin-induced glucose uptake by skeletal muscle

In obese patients with type 2 diabetes, insulin delivery to and insulin-dependent glucose uptake by skeletal muscle are delayed and impaired. The mechanisms underlying the delay and impairment are unclear. We demonstrate that impaired insulin signaling in endothelial cells, due to reduced Irs2 expression and insulin-induced eNOS phosphorylation, causes attenuation of insulin-induced capillary recruitment and insulin delivery, which in turn reduces glucose uptake by skeletal muscle. Moreover, restoration of insulin-induced eNOS phosphorylation in endothelial cells completely reverses the reduction in capillary recruitment and insulin delivery in tissue-specific knockout mice lacking Irs2 in endothelial cells and fed a high-fat diet. As a result, glucose uptake by skeletal muscle is restored in these mice. Taken together, our results show that insulin signaling in endothelial cells plays a pivotal role in the regulation of glucose uptake by skeletal muscle. Furthermore, improving endothelial insulin signaling may serve as a therapeutic strategy for ameliorating skeletal muscle insulin resistance.     

Cyclooxygenase 2 plays a pivotal role in the resolution of acute lung injury

Acute lung injury (ALI) is a severe illness with excess mortality and no specific therapy. In its early exudative phase, neutrophil activation and accumulation in the lung lead to hypoxemia, widespread tissue damage, and respiratory failure. In clinical trials, inhibition of proinflammatory mediators has not proven effective. In this study, we pursued a new investigative strategy that emphasizes mediators promoting resolution from lung injury. A new spontaneously resolving experimental murine model of ALI from acid aspiration was developed to identify endogenous proresolving mechanisms. ALI increased cyclooxygenase 2 (COX-2) expression in murine lung. Selective pharmacologic inhibition or gene disruption of COX-2 blocked resolution of ALI. COX-2-derived products increased levels of the proresolving lipid mediators lipoxin A4 (LXA4) and, in the presence of aspirin, 15-epi-LXA4. Both LXA4 and 15-epi-LXA4 interact with the LXA4 receptor (ALX) to mediate anti-inflammatory actions. ALX expression was markedly induced by acid injury and transgenic mice with increased ALX expression displayed dramatic protection from ALI. Together, these findings indicate a protective role in ALI for COX-2-derived mediators, in part via enhanced lipoxin signaling, and carry potential therapeutic implications for this devastating clinical disorder.     

Microbial Conversion of Petro-sulfur Compounds

Five substances, water soluble organic sulfur compounds, produced from dibenzothiophene by such bacteria as Pseudomonas jianii or Ps. abikonensis were isolated from culture broth. Three products of them were identified as 3-hydroxy-2-formyl-benzothiophene, dibenzothiophene-5-oxide and 3-oxo-2[3′-hydroxy-thionaphthenyl-(2)-methylene]dihydrothionaphthene respectively.     

Pollen wall development in Cryptomeria japonica (Taxodiaceae)

Pollen wall development in Cryptomeria japonica was observed by scanning and transmission electron microscopy. The pollen of C. japonica is characterized by a non-saccate, projecting papilla. The exine of C. japonica consists of the outer granular ectexine and the inner lamellated endexine. At the tetrad stage, the initial granular layer of the pro-ectexine first forms on the microspore plasma membrane. The tripartite lamellae of the pro-endexine form under the pro-ectexine. The prosporopollenin material is deposited on the pro-ectexine and pro-endexine at the free spore stage. The ectexine granule increases its volume and the endexine lamellae thicken. The papilla protrudes during the tetrad stage. The tip of the papilla bends laterally where the exine is thinner. Exine construction in C. japonica is similar to that of Cunninghamia; however, the amount and size of the granular ectexine and lamellated endexine differ. The conspicuous papilla protrudes and bends during the tetrad period.     

Size-dependent survivorship in the web-building spiderAgelena limbata

Summary Stage-specific mortality rates and mortality factors for the web-building spiderAgelena limbata, which is suggested to be food-limited, were studied, and the relationship between body size of spiders and survivorship for instar 3 to adults was examined. The mortality rate of the egg sac stage including eggs, deutova (prenymphal stage), and overwintering instar 1 nymphs was low. The low mortality of this stage was partly due to maternal care that reduced the mortality caused by predation and/or abiotic factors. From emergence of instar 1 nymphs from egg sacs to reproduction, the stagespecific mortality rates were almost constant, 32–47%, and the time-specific mortality rates were also constant. These results suggest a Deevey (1947) type II survivorship curve inA. limbata, in contrast to other reports on the wandering or burrowing spiders which suggested type III curves. Important mortality factors for nymphs and adults were parasitism by an ichneumonid wasp and predation by spiders. There were great variations in body size (carapace width) ofA. limbata in the field. Smaller individuals survived at a lower rate to the next stage than larger individuals. This tendency was clearer for the population living under poorer prey availability.A. limbata was unlikely to starve to death in the field because every stage ofA. limbata could survive starvation for a long time in the laboratory, 22–65 days on average. I suggest that the size-dependent survivorship of this spider is associated with vulnerability of smaller individuals to parasitism and predation.