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PubMed2001

Facilitated substrate transport through membrane proteins.

Substrate transport through the membrane protein maltoporin is facilitated by an affinity site in the channel. The analysis of the ion current fluctuations induced by penetration of the sugar into the channel yields the kinetic constants. Modification of the affinity site by replacing the aromatic residues suggests that nature has optimized the channel protein for maximum affinity at the extracellular side, as well as for an increased off-rate to eject a sugar trapped in the pore towards the periplasmic side.

Bacterial Outer Membrane Proteins↗

PubMed2003

Smad3: a key player in pathogenetic mechanisms dependent on TGF-beta.

Transforming growth factor-beta (TGF-beta), a key player in a large variety of physiological and disease processes, signals through transmembrane receptor serine/threonine kinases to activate novel signaling intermediates called Smad proteins, which then modulate transcription of target genes. We have utilized mice with a targeted deletion of Smad3, one of two homologous proteins involved in signaling from TGF-beta/activin, to investigate the function of this particular pathway in transducing such effects of TGF-beta. The dramatic results of the absence of Smad3 on parameters of healing of cutaneous wounds, such as reepithelialization and influx of inflammatory cells, as well as on fibrosis as modeled by radiation fibrosis of skin in mice, suggest that signaling flux through Smad3 is critical for chemotactic activity of TGF-beta, inhibitory effects of TGF-beta on keratinocyte proliferation and migration, and chemoattraction and elaboration of extracellular matrix by fibroblasts in fibrotic diseases. We recently identified a novel molecule, TLP for TRAP-1-like protein, which selectively interferes with Smad3 signaling, and are currently investigating whether levels of this protein might be altered in disease to change the relative flow of information from Smad2 and Smad3.

Animals↗

PubMed2003

Closing and inactivation potentiate the cocaethylene inhibition of cardiac sodium channels by distinct mechanisms.

Cocaethylene, a metabolite of cocaine and alcohol, is a potent inhibitor of the cardiac (Nav1.5) sodium channel heterologously expressed in Xenopus laevis oocytes. Cocaethylene produces minimal tonic block under resting conditions but causes a potent use-dependent inhibition during repetitive depolarization and a hyperpolarizing shift in the steady-state inactivation. The data are consistent with a state-dependent binding mechanism, which has high affinity for inactivated channels (KI = 17 microM) and low affinity for resting channels (KR = 185 micro). Mutations of the interdomain D3-D4 linker eliminated rapid inactivation and weakened the cocaethylene inhibition, consistent with an important role for fast inactivation in cocaethylene binding. A rapid component of cocaethylene inhibition was observed in a noninactivating mutant of Nav1.5 that was tightly linked to channel opening and displayed properties consistent with a pore blocking mechanism. Hyperpolarization caused the noninactivating mutant channel to close, trapping cocaethylene and slowing the recovery. Mutation of a conserved isoleucine (I1756C) located near the extracellular end of the D4S6 segment accelerated the recovery of the noninactivating channel, suggesting that this mutation facilitates cocaethylene untrapping, which seems to be the rate-limiting step in the recovery when the channel is closed. This contrasts with the rapidly inactivating channel, where the I1756C mutation did not alter the recovery from cocaethylene inhibition. The data suggest that additional mechanisms, such as more stable cocaethylene binding, may be a more important determinant of recovery kinetics when the channels are inactivated. The data indicate that deactivation and inactivation slow the recovery and potentiate the cocaethylene inhibition of the Nav1.5 channel by distinct mechanisms.

Animals↗

PubMed1985

Cytosolic-free calcium transients in cultured vascular smooth muscle cells: microfluorometric measurements.

Microfluorometric recordings were made of changes in the concentration of cytosolic-free calcium in cultured rat vascular smooth muscle cells treated with quin 2, an intracellularly trapped dye, under several conditions. Nitroglycerin decreased calcium in both the presence and absence of extracellular calcium and strongly and progressively decreased the extent of transient increases in calcium induced by repeated applications of caffeine in the absence of extracellular calcium. Therefore nitroglycerin probably decreases cytosolic-free calcium by accelerating the extrusion of calcium through the sarcolemmal membrane.

Aminoquinolines↗

PubMed1997

Reversed passive latex agglutination assay for detection of toxigenic Corynebacterium diphtheriae.

A reversed passive latex agglutination (RPLA) assay for determining the toxigenicity of Corynebacterium diphtheriae is presented. Rabbit antitoxin antiserum was raised by using commercially available diphtheria toxoid. This antiserum reacted with the diphtheria toxin when the culture supernatant was assayed by Western blotting, and it did not cross-react with other extracellular antigens. Affinity-purified antibodies for latex sensitization were obtained by using a Hi Trap N-hydroxysuccinimide-activated column. Demonstration of toxin in five of seven clinical isolates was in accordance with the PCR assay and the Vero cell cytotoxicity test. Culture of the bacteria for 6 h was sufficient for toxin production, and an additional 6 h was needed to observe latex agglutination. Therefore, diphtheria toxin can be detected in 12 h by this method. The lowest concentration of diphtheria toxin detectable by the RPLA assay was about 5 ng/ml. The RPLA assay can provide a convenient and reliable method for laboratories involved in the identification of toxinogenic corynebacteria.

Animals↗

PubMedDate not supplied

[TRAPS syndrome, a rare cause of fever of unknown origin: case report and review of the literature].

Tumor necrosis factor (TNF) receptor-associated periodic syndrome (TRAPS) is an autosomal dominant inherited condition of periodic fever and pain. TRAPS is caused by mutations of the TNFRSF1A gene localized at 12p13. The gene encodes extracellular region of the p55 TNF-alpha receptor, resulting in impaired cleavage and down-regulation of the membrane expressed form of the receptor, a diminished shedding of potentially antagonistic soluble form of the receptor and, as a consequence, an unbalanced TNF-alpha action. Most affected patients are from northern Europe. Fever, sterile peritonitis, pleural pain, arthralgia, myalgia, skin rash, and/or conjunctivitis occur during the syndrome episodes; some patients also develop systemic amyloidosis, with some differences among patients. An acute-phase response occurs during the episodes. We describe a case of a 23-year-old Moldavian woman, living in Italy presenting recurrent fever episodes with abdominal pain and skin rash. A biopsy showed small vessel vasculitis. The genetic analysis showed a TNFRSF1A gene (R92Q) mutation. In this paper we report also a literature review on this rare disease.

Adult↗

PubMed1983

Calcium influx is not required for TRH to elevate free cytoplasmic calcium in GH3 cells.

TRH stimulation of prolactin secretion is thought to be mediated by an elevation of free cytoplasmic Ca2+. However, whether TRH-induced influx of extracellular Ca2+ is required to elevate cytoplasmic Ca2+ remains controversial. We measured cytoplasmic free Ca2+ concentration in GH3 cells with an intracellularly trapped fluorescent indicator, Quin 2. In unstimulated cells incubated in medium containing 1.5 mM Ca2+, cytoplasmic free Ca2+ concentration was 118 +/- 18 nM (mean +/- SD). TRH (1 microM) caused a rapid transient elevation of free cytoplasmic Ca2+ to a level estimated to be at least 500 nM. High extracellular K+, which induces extracellular Ca2+ influx, caused an elevation of free cytoplasmic Ca2+ which was greater and longer in duration that that caused by TRH. When cells were incubated in medium containing 3 mM EGTA, the K+ depolarization-induced increase in free cytoplasmic Ca2+ was abolished. By contrast, the TRH-induced increase was not affected by incubating cells in medium with 3 mM EGTA, or high K+, or both; incubation of cells in medium with EGTA and high K+ abolishes the electrochemical driving force for Ca2+ influx. These data demonstrate that Ca2+ influx is not required for TRH-induced elevation of free cytoplasmic Ca2+ in GH3 cells. We conclude that in GH3 cells TRH induces an elevation of free cytoplasmic Ca2+ leading to stimulated prolactin secretion by mobilizing cellular Ca2+.

Aminoquinolines↗

PubMed1971

Intracellular accumulation of free fatty acids in isolated white adipose cells.

A simple, rapid, and accurate method was developed for measuring intracellular FFA levels in isolated white adipose cells using sucrose-(14)C or inulin carboxyl-(14)C as nontransportable, nonutilizable markers of the extracellular space. Following incubation, medium and cells were separated by centrifugation and the infranatant medium was removed by aspiration. The volume of medium trapped between cells was determined by measuring the amount of sucrose-(14)C or inulin carboxyl-(14)C retained in the floating packed adipose cells. In this way the FFA content of the adipose cells could be corrected for contamination by FFA bound to extracellular albumin. With this technique the initial events in hormone-activated lipolysis were studied under conditions of maximal and constant rates of triglyceride hydrolysis. The FFA content of isolated adipocytes of fed rats was 0.5 micro mole/g cell lipid. On addition of norepinephrine in the presence of medium albumin, the concentration of intracellular FFA rapidly increased and reached a plateau at a concentration of 2-2.5 micro moles/g cell lipid. In the presence of medium albumin an initial lag in glycerol release occurred and this was attributed to partial hydrolysis of triglyceride with retention of lower glycerides. After 5 min of incubation FFA and glycerol output was constant. In the absence of medium albumin norepinephrine-stimulated lipolysis was reduced more than 90% and extracellular FFA release was not detected. Nevertheless, intracellular FFA accumulation was identical to that seen in the presence of albumin. The data suggest that most of this intracellular pool of FFA is bound to cytoplasmic constituents.

Adipose Tissue↗

PubMed1980

Intracellular and extracellular sites of iodination in dispersed hog thyroid cells.

Iodination and hormone synthesis has been studied in isolated hog thyroid cells in suspension. We characterized three iodination processes by use of pharmacological agents. (1) Intracellular iodination dependent on active iodide transport, which was inhibited by NaClO4 or ouabain, but not by catalase. This iodination was linear for 6h with no apparent Km for iodide of 1.5 muM, was stimulated by thyrotropin or N6O2'-dibutyryladenosine 3':5'-cyclic monophosphate, yielded mostly iodinated thyroglobulin and was efficient for tetraiodothyronine synthesis. (2) Extracellular iodination, which was sensitive to catalase, but not to NaClO4 or ouabain. This iodination plateaued after 2h and the apparent Km was 16.5 muM. This process was insensitive to thyrotropin and dibutyryl cyclic AMP. The major products were iodoprotein other then thyroglobulin and iodolipid and the yield of tetraiodothyronine was low. (3) Intracellular iodination from passively diffused iodide, which was not sensitive to inhibitors. Other characteristics of passive intracellular iodination were intermediate between active intracellular iodination and extracellular iodination. The fact that the three processes are inhibited by similar concentrations of methimazole, and their apparent Km values, when corrected for the concentrating effect of iodide trapping, are all of the same order as the Km of purified thyroid peroxidases, suggest that although their locations are different, the enzymic systems involved are identical. These results show that, besides an extracellular site of iodination, dispersed thyroid cells process an intracellular site of iodination with biochemical characteristics of physiological relevance.

Animals↗

PubMed2000

Expression of the Staphylococcus hyicus lipase in Lactococcus lactis.

The extracellular Staphylococcus hyicus lipase was expressed under the control of different promoters in Lactococcus lactis and Bacillus subtilis. Its expression at high and moderate levels is toxic for the former and the latter hosts, respectively. In L. lactis, the lipase was expressed at a high level, up to 30% of the total cellular proteins, under the control of the inducible promoter PnisA. About 80% of the lipase remained associated with the cells. Close to half of this amount remained associated with the inner side of the cytoplasmic membrane as unprocessed pre-pro-lipase. The other half was trapped by the cell wall and partially degraded at the N-terminal end. This result suggests that extracellular proteases degrade the lipase. Surprisingly, the kinetics and the pattern of lipase degradation were different in the two L. lactis subspecies, L. lactis subsp. cremoris and L. lactis subsp. lactis. The extracellular proteolytic systems that degrade lipase are thus different in these closely related subspecies. The incorrect export of the lipase is not due to an inappropriate leader peptide but may be due to an inefficiency of several steps of lipase secretion. We propose that (i) the S. hyicus lipase may require a special accessory system to be correctly exported or (ii) the kinetics of lipase synthesis may be a critical factor for proper folding.

Bacillus subtilis↗

PubMed2005

Use of microdialysis to study interstitial nitric oxide and other reactive oxygen and nitrogen species in skeletal muscle.

Microdialysis techniques can be used to sample the interstitial space of tissues such as skeletal muscle. Analytical developments have allowed adaptations of these techniques to permit continuous monitoring of nitric oxide and a number of other reactive oxygen and nitrogen species in skeletal muscle extracellular space. Methods are described for assessment of interstitial nitrate and nitrite content, superoxide anion content, hydroxyl radical activity, and the content of relatively stable lipid radicals detectable using spin trapping and electron spin resonance techniques in skeletal muscle of rodents at rest and during contractile activity.

Animals↗

PubMed1995

Glutamate release and free radical production following brain injury: effects of posttraumatic hypothermia.

Posttraumatic hypothermia reduces the extent of neuronal damage in remote cortical and subcortical structures following traumatic brain injury (TBI). We evaluated whether excessive extracellular release of glutamate and generation of hydroxyl radicals are associated with remote traumatic injury, and whether posttraumatic hypothermia modulates these processes. Lateral fluid percussion was used to induce TBI in rats. The salicylate-trapping method was used in conjunction with microdialysis and HPLC to detect hydroxyl radicals by measurement of the stable adducts 2,3- and 2,5-dihydroxybenzoic acid (DHBA). Extracellular glutamate was measured from the same samples. Following trauma, brain temperature was maintained for 3 h at either 37 or 30 degrees C. Sham-trauma animals were treated in an identical manner. In the normothermic group, TBI induced significant elevations in 2,3-DHBA (3.3-fold, p < 0.01), 2,5-DHBA (2.5-fold, p < 0.01), and glutamate (2.8-fold, p < 0.01) compared with controls. The levels of 2,3-DHBA and glutamate remained high for approximately 1 h after trauma, whereas levels of 2,5-DHBA remained high for the entire sampling period (4 h). Linear regression analysis revealed a significant positive correlation between integrated 2,3-DHBA and glutamate concentrations (p < 0.05). Posttraumatic hypothermia resulted in suppression of both 2,3- and 2,5-DHBA elevations and glutamate release. The present data indicate that TBI is followed by prompt increases in both glutamate release and hydroxyl radical production from cortical regions adjacent to the impact site. The magnitude of glutamate release is correlated with the extent of the hydroxyl radical adduct, raising the possibility that the two responses are associated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1981

Measurement of rapidly exchangeable cellular calcium in the perfused beating rat heart.

Although Ca2+ has long been known to play a vital role in excitation--contraction coupling in the heart, investigation of the details of this role has been hampered by the experimental difficulty of measuring Ca2+ movements through the different compartments of the cell. A major problem has been to distinguish the relatively small amount of rapidly exchangeable cellular Ca2+ from the large amount of vascular and interstitial Ca2+. We report here a method that overcomes this problem. Rat hearts were labeled by perfusion at 37 degrees C with medium containing 45Ca2+. They were then cooled, and extracellular 45Ca2+ was removed by perfusion at 6 degrees C with Ca2+-free medium. Cellular 45Ca2+ that had been trapped in the hearts by cooling was then released by reperfusion at 37 degrees C with medium containing unlabeled Ca2+. The cellular origin of this 45Ca2+ was confirmed by using [3H]sucrose: When hearts were also labeled with [3H]sucrose, very little [3H]-sucrose was released with the 45Ca2+ peak. The amount of exchangeable cellular Ca2+ in hearts labeled for 5 min was 125 +/- 13 nmol/g of wet weight. The half-time for its release was less than 1 min. This cellular Ca2+ contained at least two pools: a rapidly exchanging pool that required extracellular Ca2+ for release (pool A, 38% of total), and a more slowly exchanging pool that did not (pool B, 62% of total). Hearts stimulated with isoproterenol during the 5-min labeling period showed an increase of 46% for the total amount of exchangeable cellular Ca2+; this increase was entirely located in pool A.

Animals↗

PubMed1989

Free radicals induced by adriamycin-sensitive and adriamycin-resistant cells: a spin-trapping study.

The radicals generated by adriamycin-sensitive (CHO-AB) and adriamycin-resistant (CHO-C5) Chinese hamster ovary cells as well as by adriamycin-sensitive and -resistant human breast cancer cells (MCF7-WT and MCF7-ADR) have been studied with spin-trapping and ESR spectroscopy. During anoxic exposure to adriamycin (ADR) both pairs of cell lines produced the broad ESR singlet characteristic of ADR semiquinone (AQ.). By use of tris(oxalato)chromate (CrOx) as an extracellular line-broadening agent, the distribution of AQ. between the intra- and extracellular compartments was studied. For cell densities of (1-3) X 10(7) cells/mL, CrOx eliminated most, though not all, of the ESR signal, indicating that the AQ. radicals freely diffuse and partition between the intra- and extracellular compartments proportionally to their respective volumes. Similar behavior was exhibited by all four cell lines studied. Upon introduction of oxygen to anoxic cells in the presence of the spin trap 5,5-dimethylpyrroline N-oxide (DMPO), the AQ. signal was replaced by that of the DMPO-OH spin adduct. Metal chelators such as desferrioxamine had no effect on DMPO-OH or AQ. formation. Superoxide dismutase, not catalase, totally eliminated the ESR signal, indicating that DMPO-OH produced by ADR-treated cells originates from superoxide rather than from .OH produced from H2O2. In the presence of CrOx, the DMPO-OH signal was not distinguishable from the background noise, thus excluding any contribution to the signal by intracellular spin adducts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2006

Discovery, cloning and heterologous expression of secreted potato proteins reveal erroneous pre-mRNA splicing in Aspergillus oryzae.

A novel transposon assisted signal trapping (TAST) technology, developed to specifically select only the secreted proteins, was used to discover novel extracellular plant proteins from Solarium tuberosum infected with Phytophthora infestans. Analysis of 384 hits provided 191 P. infestans and S. tuberosum sequences of secreted proteins, with an approx. 2/3 of these originating from potato. Subsequent screening for interesting genes was carried out using bioinformatics. A selected variety of the discovered sequences are presented, including a novel S. tuberosum xyloglucan endotransglucosylase (StXTH), which was cloned and subjected to detailed heterologous expression studies in Aspergillus oryzae. RT-PCR analysis of mRNA from A. oryzae StXTH1 transformants revealed that parts of the mRNA pool had been incorrectly processed, and only weak and inconsistent indications of active protein could be detected. A high AT content of StXTH1 and the occurrence of A. oryzae intron donor, acceptor, and branch point recognition sites resulted in erroneous intron interpretation (cryptic introns) of parts of the mRNA coding sequence. This may explain the difficulties generally experienced in expressing plant genes in filamentous fungi.

Aspergillus oryzae↗

PubMed1997

Expression of rat thrombin receptor and mutants in the baculovirus-infected insect cell system.

The rat thrombin receptor (TR-1) has been expressed in Sf9 cells. Two mutant receptors, one lacking a thrombin cleavage site (RTRM), and the other containing only the extracellular domain of the receptor (ECD), have been expressed. Antibodies to the thrombin receptor activating peptide (TRAP) and to the fibrinogen-binding exosite have been prepared. On Western blots these antibodies bound to TR-1 bands of 65-70 kDa and 44 kDa, similar bands for RTRM, and a doublet of about 10 and 12 kDa for ECD. The free cytosolic Ca++ concentration, measured by Fura-2, increased after thrombin or TRAP stimulation in the cells expressing TR-1. The RTRM cells did not respond to thrombin and had an attenuated response to TRAP. The ECD protein was found in the medium; it was not glycosylated. Both the mutants and the antibodies should be useful for studies of TR-1 structure and function.

Animals↗

PubMed1995

Benzene oxidation coupled to sulfate reduction.

Highly reduced sediments from San Diego Bay, Calif., that were incubated under strictly anaerobic conditions metabolized benzene within 55 days when they were exposed initially to 1 (mu)M benzene. The rate of benzene metabolism increased as benzene was added back to the benzene-adapted sediments. When a [(sup14)C]benzene tracer was included with the benzene added to benzene-adapted sediments, 92% of the added radioactivity was recovered as (sup14)CO(inf2). Molybdate, an inhibitor of sulfate reduction, inhibited benzene uptake and production of (sup14)CO(inf2) from [(sup14)C]benzene. Benzene metabolism stopped when the sediments became sulfate depleted, and benzene uptake resumed when sulfate was added again. The stoichiometry of benzene uptake and sulfate reduction was consistent with the hypothesis that sulfate was the principal electron acceptor for benzene oxidation. Isotope trapping experiments performed with [(sup14)C]benzene revealed that there was no production of such potential extracellular intermediates of benzene oxidation as phenol, benzoate, p-hydroxybenzoate, cyclohexane, catechol, and acetate. The results demonstrate that benzene can be oxidized in the absence of O(inf2), with sulfate serving as the electron acceptor, and suggest that some sulfate reducers are capable of completely oxidizing benzene to carbon dioxide without the production of extracellular intermediates. Although anaerobic benzene oxidation coupled to chelated Fe(III) has been documented previously, the study reported here provides the first example of a natural sediment compound that can serve as an electron acceptor for anaerobic benzene oxidation.

Journal Article↗

PubMed1999

[Genetic approach to the study of the sporogonic cycle in Plasmodium].

The development of transformation and mutagenesis techniques of the two species of Plasmodium most studied--Plasmodium falciparum (human parasite) and Plasmodium berghei (rodent parasite)--opens new perspectives for the molecular study on the parasite sporogonic cycle in the insect vector. The parasite's stages that can be genetically transformed (the asexual erythrocytic stages) and gametocytes. The function of proteins coded by genes present in single copy in the genome can thus be studied after only one recombination. Furthermore, most of the genes expressed during the sporogonic cycle are not during the erythrocytic stages, which makes possible the isolation of the erythrocytic cycles of parasites with a mutation in a gene which is essential to the development of the sporogonic cycle. Finally, the Plasmodium berghei model is particularly advantageous in that the entire cycle of this species of Plasmodium can be easily maintained in the laboratory. The species also appears to be easier to manipulate genetically than Plasmodium falciparum. Let us take the example of two surface proteins of Plasmodium sporozoites: the circumsporozoite proteins (CS) and the thrombospondin-related anonymous protein (TRAP). Both of these proteins have already been characterized in detail. Each of them possesses motives present in numerous protein of cell-cell or extracellular cell-matrice adhesion. The selective destruction of both genes has shown that both proteins also play a role in the development of the parasite within the mosquito. The CS protein is essential to the formation of sporozoites in the mosquito's intestinal oocysts, whereas the TRAP protein is essential for the sporozoites to have the power to invade the secreting cells of the mosquito's salivary glands as well as the host's hepatocytes. Using the mutagenous system for P. berghei should thus help elucidate the function of the important products expressed by the parasite during its development cycle in the vector mosquito as well as analyse the structure-function relationship of these products. It is possible that the molecular dissection of the parasite-mosquito interaction will lead to new approaches in the prevention of parasite transmission.

Animals↗