The N-glycans of jack bean alpha-mannosidase. Structure, topology and function

The acid hydrolase alpha-mannosidase, which accumulates in plant vacuoles and probably is involved in the catabolism and turnover of N-linked glycoproteins, is itself a glycoprotein with at least one high-mannose-type and one complex-type N-glycan. The puzzling finding that alpha-mannosidase stably carries its own substrate suggests that the N-glycans have unique topologies, and important functions in protein folding, oligomerization or enzyme activity. As a first step towards the elucidation of this enigma, we purified the N-glycans of jack bean alpha-mannosidase and determined their structures by sugar composition analysis, mass spectrometry and 1H-NMR. The structures of two N-glycans were identified in an approximate ratio of one-to-one: a glucose-containing high-mannose-type glycan (Glc1Man9GlcNAc2) and a small xylose- and fucose-containing complex-type glycan (Xyl1Man1Fuc1GlcNAc2). Isolation and sequencing of glycopeptides strongly suggests that one high-mannose-type and one complex-type glycan are linked to specific glycosylation sites of the large alpha-mannosidase subunit. The high-mannose-type glycan, which is a good substrate of the endoglycosidase (endo-H), can only be removed from the enzyme after denaturation and cleavage of disulfide bonds by a reducing agent, suggesting that this glycan is buried within the folded polypeptide and, thus, protected from its hydrolytic activity. Denaturation and reduction of the native enzyme led to a marked decrease in alpha-mannosidase activity. However, the activity could largely be recovered by renaturation in an appropriate renaturation buffer. In contrast, recovery of alpha-mannosidase activity failed when the high-mannose-type glycan was removed by endo-H prior to renaturation, indicating that this glycan appears to be important for enzyme activity.

CD24 promotes invasion of glioma cells in vivo

Based on the hypothesis that adhesion molecules expressed on the surface of glioma cells mediate brain invasion, we examined the effect of CD24 on growth and migration of gliomas in vitro and in vivo. CD24, a glycosylphosphatidylinositol anchored, highly glycosylated adhesion molecule, is expressed in hematopoietic and neural cells. We found immunohistochemical expression of CD24 in human glioblastomas. We then established a clone from C6 rat glioblastoma cells, where mouse CD24 (also called heat stable antigen) is under control of a tetracycline-responsive promoter. In the presence of tetracycline (1 microg/ml) CD24 was downregulated by 20-fold. In vitro migration assays were performed on a basement membrane preparation (matrigel) and on myelin, the main substrates of in vivo glioma migration. While the cells were more motile on matrigel as compared with myelin, no relation between CD24 expression and motility was observed. We then transplanted the C6 clone into the striatum of nude mice and regulated CD24 expression via tetracycline in the drinking water (1 mg/ml). After 3 weeks, CD24 positive tumors of mice getting no tetracycline showed diffuse invasion of tumor cells in a brain area 10-fold larger than in CD24-suppressed tumors of mice receiving tetracycline. These data show that CD24 stimulates migration of gliomas in vivo and they suggest a role for this adhesion molecule in diffuse brain invasion of human gliomas.

Antisense repression of vacuolar and cell wall invertase in transgenic carrot alters early plant development and sucrose partitioning

To unravel the functions of cell wall and vacuolar invertases in carrot, we used an antisense technique to generate transgenic carrot plants with reduced enzyme activity. Phenotypic alterations appeared at very early stages of development; indeed, the morphology of cotyledon-stage embryos was markedly changed. At the stage at which control plantlets had two to three leaves and one primary root, shoots of transgenic plantlets did not separate into individual leaves but consisted of stunted, interconnected green structures. When transgenic plantlets were grown on media containing a mixture of sucrose, glucose, and fructose rather than sucrose alone, the malformation was alleviated, and plantlets looked normal. Plantlets from hexose-containing media produced mature plants when transferred to soil. Plants expressing antisense mRNA for cell wall invertase had a bushy appearance due to the development of extra leaves, which accumulated elevated levels of sucrose and starch. Simultaneously, tap root development was markedly reduced, and the resulting smaller organs contained lower levels of carbohydrates. Compared with control plants, the dry weight leaf-to-root ratio of cell wall invertase antisense plants was shifted from 1:3 to 17:1. Plants expressing antisense mRNA for vacuolar invertase also had more leaves than did control plants, but tap roots developed normally, although they were smaller, and the leaf-to-root ratio was 1.5:1. Again, the carbohydrate content of leaves was elevated, and that of roots was reduced. Our data suggest that acid invertases play an important role in early plant development, most likely via control of sugar composition and metabolic fluxes. Later in plant development, both isoenzymes seem to have important functions in sucrose partitioning.

Tissue-specific expression of two genes for sucrose synthase in carrot (Daucus carota L.)

Sucrose synthase, which cleaves sucrose in the presence of uridine diphosphate (UDP) into UDP-glucose and fructose, is thought to be a key determinant of sink strength of heterotrophic plant organs. To determine the roles of the enzyme in carrot, we characterized carrot sucrose synthase at the molecular level. Two genes (Susy*Dc1 and Susy*Dc2) were isolated. The deduced amino acid sequences are 87% identical. However, the sequences upstream of the translation initiation codons are markedly different, as are the expression patterns of the two genes. Susy*Dc2 was exclusively expressed in flowers. Transcripts for Susy*Dc1 were found in stems, in roots at different developmental stages, and in flower buds, flowers and maturing seeds, with the highest levels in strong utilization sinks for sucrose such as growing stems and tap root tips. Expression of Susy*Dc1 was regulated by anaerobiosis but not by sugars or acetate. The carrot sucrose synthase protein is partly membrane-associated and this insoluble form may be directly involved in cellulose biosynthesis. Tap roots of the carrot cultivar used accumulated starch in the vicinity of the vascular bundles, which correlated with high sucrose synthase transcript levels. This finding suggests that soluble sucrose synthase in tap roots channels sucrose towards starch biosynthesis. Starch accumulation appears to be transient and may be involved in sucrose partitioning to developing tap roots.

Altered cholinesterase and monooxygenase levels in Daphnia magna and Chironomus riparius exposed to environmental pollutants

Biochemical indices were investigated for their potential use as variables of sublethal toxicity in Daphnia (cholinesterase) and Chironomus (cholinesterase and biotransformation enzymes). Parathion, dichlorvos, and aldicarb caused dose-related inhibition of cholinesterase (ChE) in 24-h bioassays with both species. Ratios of Daphnia and Chironomus ChE IC50 values to corresponding immotility EC50 values derived from the same experiment covered the range 0.26 to 1.2. Estimates of the ChE inhibition caused by the immotility EC50 were in the range 53-99% below control activity. ChE IC50 values of dichlorvos, parathion, and aldicarb were 0.17, 0.61, and 95 microg/liter in Daphnia and 6.2, 2.9, and 27 microg/liter in Chironomus, respectively. Cytochrome P450-dependent monooxygenase activities (ethoxyresorufin-O-deethylase, methoxyresorufin-O-deethylase, and ethoxycoumarin-O-deethylase) were detectable in Chironomus but not in Daphnia. Chironomus monooxygenase activities were significantly inhibited to about 30% of control values after 4 days of exposure to 50 microg/liter 3, 4-dichloroaniline but remained unchanged by 0.5 microg/liter parathion. An approximately 1.3-fold induction of monooxygenase activities was caused by the model inducer naphthalene (0.1mg/liter). These results suggest that cytochrome P450-dependent monooxygenase activities may be useful variables in toxicity tests with aquatic insects.

Characterization of source- and sink-specific sucrose/H+ symporters from carrot

To understand how sucrose (Suc) is transported from source leaves to developing tap roots of carrot (Daucus carota L.), we cloned two cDNAs (DcSUT1 and DcSUT2) for proteins with homologies to plant Suc/H+ symporters. The deduced polypeptide sequences are 52% identical and have 12 predicted membrane-spanning domains each. Transport activities were confirmed by expression of the clones in yeast cells. Both transporters had optimal activity below pH 5.0 and Michaelis constant values of 0.5 mM. Suc uptake was inhibited by protonophores, suggesting that Suc transport is linked to the proton electrochemical potential across the plasma membrane. DcSUT1 and DcSUT2 had markedly different expression patterns. Transcripts of DcSUT1 were found only in the green parts of plants, with highest levels in the lamina of source leaves, indicating that DcSUT1 is required for the loading of Suc into the phloem. In leaf lamina expression was diurnally regulated, suggesting that Suc export from the leaves is higher during the day than during the night. The mRNA of DcSUT2 was found mainly in sink organs, and no diurnal expression pattern was detected in the storage root. Here, expression was not restricted to the phloem but was much higher in storage parenchyma tissues of phloem and xylem. The close relationship of DcSUT2 with a Suc/H+ symporter from fava bean, which facilitates Suc uptake into the cotyledons of developing seeds, indicates that this carrot Suc transporter may be involved in loading Suc into storage parenchyma cells.

Use of conventional and self-adjusting nasal continuous positive airway pressure for treatment of severe obstructive sleep apnea syndrome: a comparative study

STUDY OBJECTIVES

To compare conventional and self-adjusting nasal continuous positive airway pressure (nCPAP) therapy in patients with severe obstructive sleep apnea syndrome with respect to suppression of respiratory disturbances, quality of sleep, mean mask pressure, and patient compliance.

DESIGN

Cohort study of consecutive patients with obstructive sleep apnea syndrome, single-blinded.

SETTING

Clinical sleep laboratory in Germany.

PATIENTS

Fifty patients (44 men, 6 women who ranged in age from 35 to 71 years) with polysomnographically confirmed severe obstructive sleep apnea syndrome (respiratory disturbance index [RDI], >20/h).

MEASUREMENTS AND INTERVENTIONS

After baseline polysomnography, patients were randomly treated with nCPAP either in conventional (group 1) or in automatically adjusting (group 2) mode. Three to 6 months after adjustment, all patients underwent polysomnography again. They also were examined with a portable monitoring device and received a questionnaire on subjective well-being and device evaluation.

RESULTS

Anthropometric and respiratory data were comparable in both groups; body mass index had not changed significantly in the follow-up. RDI dropped by 91.5% (from 38.3+/- 13.9/h to 3.6+/-4.4/h) in conventional and by 93.6% (from 35.5+/-9.6/h to 2.4+/-1.6/h) in self-adjusting mode (statistically not significant [NS]). Sleep efficiency decreased by 4.0% in conventional and increased by 2.0% in self-adjusting mode (NS). In both groups, normal sleep structure was largely restored. Mean mask pressure was 8.1+/-2.5 cm H2O in group 1 and 6.5+/-1.7 cm H2O in group 2 (p<0.01). Patient compliance in terms of nights per week of mask appliance was better in the self-adjusting mode (5.7+/-0.7 to 6.5+/-0.4; p<0.01).

CONCLUSION

Self-adjusting nCPAP demonstrates the same reliability in suppression of respiratory disturbances as fixed-mask pressure therapy. Sleep quality is slightly superior, patient compliance is highly significantly better.

Two isoforms of plant RAD23 complement a UV-sensitive rad23 mutant in yeast

DNA repair by nucleotide excision (NER) has been demonstrated in plant cells at the biochemical level but until now none of the molecular components of the plant NER complex has been identified. In this paper, the cloning and characterization of two isoforms of RAD23 from carrot (Daucus carota L.) are reported. It has been suggested that RAD23 in yeast is an assembly factor of the NER complex required for transcription-coupled repair as well as efficient overall genome repair. A functional assay demonstrated that both plant homologues complement the UV-sensitive phenotype of a rad23 deletion mutant of yeast. This result suggests that homologous polypeptides may catalyse NER in plants and yeast and, possibly, by a similar mechanism.

Pulmonary hypertension in patients with obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is associated with an increased cardiovascular morbidity, including pulmonary hypertension. Little is known about factors influencing the degree of pulmonary hypertension and left ventricular dysfunction in patients with OSAS, especially in the absence of concomitant lung disease.

METHODS

Right heart catheterization, arterial blood gas analysis, and pulmonary function tests were performed in 92 consecutive patients (81 men and 11 women; mean +/- SD age, 53.1 +/- 11.0 years) with polysomnographically verified OSAS, in whom clinically significant lung disease was excluded.

RESULTS

Eighteen patients (20%) had mild pulmonary hypertension; 8 (44%) of them also had increased pulmonary capillary wedge pressures (Ppew). Left ventricular dysfunction was associated with arterial hypertension. Only Ppcw (r = 0.51; P < .001) and the percentage of time during sleep spent with an oxygen saturation below 90% (as an indicator of the severity of OSAS) (r = 0.34; P = .003) were significantly and independently associated with pulmonary artery pressure.

CONCLUSIONS

Obstructive sleep apnea syndrome can cause mild pulmonary hypertension, even in the absence of pulmonary disease. In these patients, pulmonary hypertension is of the postcapillary type, or-in patients with normal left ventricular function-strongly related to the severity of OSAS. Our findings indicate that OSAS may constitute an important, and independent, risk factor for pulmonary hypertension.

Right ventricular dysfunction in patients with obstructive sleep apnoea syndrome

There is conclusive evidence that obstructive sleep apnoea syndrome (OSAS) influences right heart haemodynamics and can also induce pulmonary hypertension. It is not known, however, whether right ventricular dysfunction can occur in patients with OSAS in the absence of lung disease. We studied 107 patients (94 males, 13 females, mean age 55 +/- 11 yrs) with polysomnographically verified OSAS in whom clinically significant lung disease was excluded. Right ventricular ejection fraction (RVEF) was determined by radionuclide ventriculography. In addition, pulmonary function tests, arterial blood gas analysis and right heart catheterization were performed. RVEF was impaired in 19 patients (18%). Eighteen (95%) had signs or symptoms consistent with mild right ventricular failure. Patients with or without impaired RVEF did not differ with respect to body mass index, age or lung function. Stepwise multiple logistic regression analysis revealed that RVEF was significantly associated with the apnoea/hypopnoea index (r = -0.68; p = 0.0009) and the extent of nocturnal oxyhaemoglobin saturation (r = 0.42; p = 0.035), but not with age, body mass index, blood gas analysis, gender, lung function, pulmonary artery pressure and left ventricular ejection fraction. We conclude that in patients with otherwise unexplained right ventricular failure, obstructive sleep apnoea syndrome may underlie the right ventricular dysfunction.

[Pronounced hypersomnia in a 13-year-old patient with periodic leg movements]

We report on a rare case of a thirteen-year old female with excessive daytime somnolence, which was caused by periodic leg movement. This underlines the necessity first to consider this diagnosis and second to record unconditionally the EMG derivation at minimum of the tibialis muscles in all patients with hypersomnolence. Even if carbamazepine is not the treatment of choice, in this case it was of remarkable effect.

Prostaglandin effects on the contractility of bovine trabecular meshwork and ciliary muscle

The ocular hypotensive activity of prostaglandins (PGs) has previously been demonstrated in various species including man. The underlying mechanism of action of prostanoids other than PGF2 alpha remains contentious. Because the trabecular meshwork and ciliary muscle are believed to have a role in the regulation of aqueous humor outflow, the aim of this study was to identify the PG-receptor subtypes present in these tissues using receptor-selective agonists. Contractions of isolated strips of bovine trabecular meshwork and ciliary muscle were recorded isometrically in continuously perfused tissue chambers. Contractile activity of PGs was determined relative to a maximally effective concentration of carbachol (1 microM) as a standard agonist. The following prostanoids were employed: PGF2 alpha, 17-phenyl PGF2 alpha (FP-receptor agonists), sulprostone (EP3 > EP1-agonist), AH13205 (EP2-agonist), 11-deoxy PGE1 (non-selective EP-agonist), and U-46619 (TP-agonist). The thromboxane-mimetic U-46619 elicited a strong contraction of the trabecular meshwork with the highest concentration (1 microM) being almost twice as efficacious (186.6%) as the maximal carbachol concentration, whereas the effect on the ciliary muscle was small. The U-46619 induced trabecular meshwork contraction could be blocked with a potent and selective TP-receptor antagonist, 1 microM SQ29548, indicating the involvement of TP-receptors. The other PG-analogs studied had either no or a small but statistically significant effect. Thus, 17-phenyl PGF2 alpha (1 microM) weakly contracted the ciliary muscle (4.8%), sulprostone (1 microM) the trabecular meshwork (10.1%), 11-deoxy PGE1 (1 microM) and AH13205 (10 microM) elicited relaxations in both tissue precontracted with carbachol (1 microM). The relaxant effects were more pronounced in trabecular meshwork (15.6% for 11-deoxy PG1 and 21.4% for AH13205) than ciliary muscle (6.8 and 7.4% respectively). PGF2 alpha did not elicit a significant response in either tissue. Our studies suggest the existence of TP- and EP2-receptors in the bovine trabecular meshwork and potentially FP- and EP2-receptors in the ciliary muscle. In conclusion, thromboxane-mimetics and EP2-agonists have opposing activities on contractile elements in the meshwork and may modulate trabecular outflow in a functionally antagonistic manner. Prostanoid effects on ciliary muscle appear rather modest compared to parasympathomimetic drugs. It is conceivable that TP-agonists may substantially affect trabecular outflow.

Purification and characterization of neutral and alkaline invertase from carrot

Neutral and alkaline invertase were identified in cells of a suspension culture of carrot (Daucus carota L.) and purified to electrophoretic homogeneity. Neutral invertase is an octamer with a molecular mass of 456 kD and subunits of 57 kD, whereas alkaline invertase is a tetramer with a molecular mass of 504 kD and subunits of 126 kD. Both enzymes had sharp pH profiles, with maximal activities at pH 6.8 for neutral invertase and pH 8.0 for alkaline invertase, and both hydrolyzed sucrose with typical hyperbolic kinetics and similar Km values of about 20 mM at pH 7.5. Neutral invertase also hydrolyzed raffinose and stachyose and, therefore, is a beta-fructofuranosidase. In contrast, alkaline invertase was highly specific for sucrose. Fructose acted as a competitive inhibitor of both enzymes, with Ki values of about 15 mM. Glucose was a noncompetitive inhibitor of both neutral and alkaline invertase, with a Ki of about 30 mM. Neither enzyme was inhibited by HgCl2. Alkaline invertase was markedly inhibited by CaCl2, MgCl2, and MnCl2, and neutral invertase was not. In contrast to alkaline invertase, neutral invertase was inhibited by the nucleotides ATP, CTP, GTP, and UTP.

Molecular characterization and functional analysis of sucrose-cleaving enzymes in carrot (Daucus carota L.)

The amount of carbon transported into storage organs of crop plants to a large degree determines crop yield. The role of sucrose-cleaving enzymes in this process is not clear and it is the main goal of our work to tackle this question. Sucrose cleavage is catalysed either by invertase or sucrose synthase both of which exist in several isoforms with different subcellular locations. Carrot (Daucus carota L.) contains three major isoenzymes of acid invertase, which either accumulate as soluble polypeptides in the vacuole (isoenzymes I and II) or are ionically bound to the cell wall. Carrot sucrose synthase is thought to be a cytoplasmic enzyme encoded by two genes. cDNA clones have been isolated and characterized for cell wall invertase, for isoenzymes I and II of vacuolar invertase, and for sucrose synthase. Gene-specific fragments of these clones were used to determine the steady-state levels of transcripts in the prominent sink and source organs of developing carrot plants. The expression patterns of each gene were different and were organ- and development-specific. Developing tap roots contained only transcripts for isoenzyme II of vacuolar invertase and sucrose synthase. The source/sink balance of these plants was manipulated and only the expression of these two genes was markedly altered, indicating their importance in sucrose partitioning. Based on these results, a model is proposed for sucrose partitioning in carrot plants with developing tap roots in which sucrose synthase regulates sucrose utilization, whereas isoenzyme II of vacuolar invertase controls sucrose storage and sugar composition.

[Coronary heart disease in patients with obstructive sleep apnea]

OBJECTIVE

As patients with severe obstructive sleep apnoea (OSA) have increased cardiovascular morbidity and mortality rates, the prevalence of coronary heart disease (CHD) was investigated in patients with OSA proven by polysomnography (apnoea/hypopnea index > or = 10/h).

PATIENTS AND METHODS

In 440 patients (400 men, 40 women; mean age 55.3 [16-80] years) with OSA proven by polysomnography, the possible diagnosis of CHD was assessed by history, physical examination, ECG at rest and on exercise, one- and two-dimensional echocardiography and, where indicated, myocardial scintigraphy and coronary angiography.

RESULTS

CHD was demonstrated by angiography in 24.6% (men: 26.4%; women: 7.5%). Adding patients with CHD diagnosed noninvasively, but unconfirmed by angiography, positive correlation was found in 33.2% (men: 34.8%; women: 17.5%).

CONCLUSION

There was a high prevalence of CHD in patients with OSA. This underlines the importance of careful cardiac diagnosis in patients with OSA.

[Treatment of radiotherapy-induced gastroparesis with erythromycin]

HISTORY

A 75-year-old woman who had undergone a hysterectomy with adnexectomy followed by radiotherapy for endometrial carcinoma complained of postprandial nausea with vomiting after eating solid foods and of cramp-like abdominal pain, but her appetite was good. She had lost 25 kg in weight over 13 months.

EXAMINATION

Physical examination, laboratory tests, radiology and gastroscopy were unremarkable. Gastric scintigraphy showed abnormally prolonged emptying.

TREATMENT AND COURSE

Nausea and vomiting stopped at once after erythromycin (a motilin agonist) had been administered. It was at first given intravenously after meals (50 mg three times daily for 5 days), then orally for 10 weeks (250 mg three times daily before meals). Subsequent examination revealed normal gastric emptying. The symptoms did not recur after erythromycin had been discontinued.

CONCLUSION

Erythromycin is an effective drug against gastroparesis caused by radiotherapy, because it acts even when the enteric nerves are damaged.