PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Secretion systems”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources
PubMed2005

XcpX controls biogenesis of the Pseudomonas aeruginosa XcpT-containing pseudopilus.

Pseudomonas aeruginosa is an opportunistic gram-negative pathogen equipped with multiple secretion systems. The type II secretion machinery (Xcp secreton) is involved in the release of toxins and enzymes. The Xcp secreton is a multiprotein complex, and most of its components share homology with proteins involved in type IV pili biogenesis. Among them, the XcpT-X pseudopilins possess characteristics of the major constituent of the type IV pili, the pilin PilA. We have shown previously that XcpT can be assembled in a multifibrillar structure that was called the pseudopilus. By using two different microscopic approaches, we show here that the pseudopili are preferentially isolated fibers rather than tight bundles. Moreover, none of the other four pseudopilins are able to form a pseudopilus, suggesting that the assembly of such a structure is a unique property of XcpT. Moreover, we show that 5 of the 12 Xcp proteins are not required for pseudopilus biogenesis, whereas they are for type II secretion. Most interestingly, we showed that one pseudopilin, XcpX, controls the assembly of XcpT into a pseudopilus. Indeed, when the number of XcpX subunits increases, the length of the pseudopilus decreases. Conversely, in the absence of XcpX, the pseudopilus length is abnormally long. Our results indicate that XcpT and XcpX directly interact with each other. Furthermore, this interaction induces a clear destabilization of XcpT. The interaction between XcpT and XcpX could be part of the molecular mechanism underlying the dynamic control of pseudopilus elongation, which could be crucial for type II-dependent protein secretion.

Bacterial Adhesion↗
PubMed1975

Microfilamentous system and secretion of enzyme in the exocrine pancreas. Effect of cytochalasin B.

The microfilaments in the acinar cell of the exocrine pancreas are essentially located in the apical part of the cell: thin microfilaments (50 A), cytochalasin B (CB)-sensitive, form the axis of the microvilli and a network lying beneath the apical membrane; thicker filaments (100 A), at least partly CB-insensitive, form bundles parallel to the plasma cell membrane and the desmosomal links. CB interaction with the acinar cell of the exocrine pancreas involves at least two sites: a membrane site involved in the inhibitory effect of CB on the monosaccharide transport and a less sensitive site at the filamentous level at least partly responsible for the inhibitory effect of CB in the secretion of the exportable enzyme from the pancreatic cell. CB did not alter the energy balance of the acinar cell nor the exchanges of 15-Ca between the extracellular medium and the pancreatic tissue. CB (2 times 10-minus 7 and 2 times 10-minus 6 M) has secretagogue properties whereas CB (2 times 10-minus 5 M) has inhibitory effect on stimulated secretion and secretagogue properties. The mechanism of these secretory effects is not yet explained. The analysis presented in this investigation affords strong evidence for the involvement of the microfilamentous network in the last steps of the secretory cycle in the acinar cell of the exocrine pancreas.

Adenosine Triphosphate↗
PubMed2006

The TraA relaxase autoregulates the putative type IV secretion-like system encoded by the broad-host-range Streptococcus agalactiae plasmid pIP501.

The conjugative multiple antibiotic resistance plasmid pIP501 can be transferred and stably maintained in a variety of Gram-positive genera, including multicellular Streptomyces lividans, as well as in Gram-negative Escherichia coli. The 15 putative pIP501 transfer (tra) genes are organized in an operon-like structure terminating in a strong transcriptional terminator. This paper reports co-transcription of the pIP501 tra genes in exponentially growing Enterococcus faecalis JH2-2 cells, as shown by RT-PCR. The tra genes are expressed throughout the life cycle of Ent. faecalis, and the expression level is independent of the growth phase. Electrophoretic mobility shift assays indicated that the TraA relaxase, the first gene of the tra operon, binds to the tra promoter P(tra), which partially overlaps with the origin of transfer (oriT). DNase I footprinting experiments further delimited the TraA binding region and defined the nucleotides bound by TraA. Beta-Galactosidase assays with P(tra)-lacZ fusions proved P(tra) promoter activity, which was strongly repressed when TraA was supplied in trans. Thus, it is concluded that the pIP501 tra operon is negatively autoregulated at the transcriptional level by the conjugative DNA relaxase TraA.

Bacterial Proteins↗
PubMed2006

AopP, a type III effector protein of Aeromonas salmonicida, inhibits the NF-kappaB signalling pathway.

Aeromonas salmonicida subsp. salmonicida contains a functional type III secretion system that is responsible for the secretion of the ADP-ribosylating toxin AexT. In this study, the authors identified AopP as a second effector protein secreted by this system. The aopP gene was detected in both typical and atypical A. salmonicida isolates and was found to be encoded on a small plasmid of approximately 6.4 kb. Sequence analysis indicates that AopP is a member of the YopJ family of effector proteins, a group of proteins that interfere with mitogen-activated protein kinase (MAPK) and/or nuclear factor kappa B (NF-kappaB) signalling pathways. AopP inhibits the NF-kappaB pathway downstream of IkappaB kinase (IKK) activation, while a catalytically inactivated mutant, AopPC177A, does not possess this inhibitory effect. Unlike other effectors of the YopJ family, such as YopJ and VopA, AopP does not inhibit the MAPK signalling pathway.

Aeromonas salmonicida↗
PubMed2006

Down-regulation of key virulence factors makes the Salmonella enterica serovar Typhimurium rfaH mutant a promising live-attenuated vaccine candidate.

Mutants of Salmonella enterica serovar Typhimurium that lack the transcriptional regulator RfaH are efficient as live oral vaccines against salmonellosis in mice. We show that the attenuation of the vaccine candidate strain is associated with reduced net growth in epithelial and macrophage cells. In order to identify the relevant RfaH-dependent genes, the RfaH regulon was determined with S. enterica serovars Enteritidis and Typhimurium using whole-genome Salmonella microarrays. As well as impacting the expression of genes involved in lipopolysaccharide (LPS) core and O-antigen synthesis, the loss of RfaH results in a marked down-regulation of SPI-4 genes, the flagellum/chemotaxis system, and type III secretion system 1. However, a proportion of these effects could have been the indirect consequence of the altered expression of genes required for LPS biosynthesis. Direct and indirect effects of the rfaH mutation were dissociated by genome-wide transcriptional profiling of a structural deep-rough LPS mutant (waaG). We show that truncation of LPS itself is responsible for the decreased intracellular yield observed for DeltarfaH strains. LPS mutants do not differ in replication ability; rather, they show increased susceptibility to antimicrobial peptides in the intracellular milieu. On the other hand, evidence that deletion of rfaH, as well as some other genes involved in LPS biosynthesis, results in enhanced invasion of various mammalian cells is shown. Exposure of common minor antigens in the absence of serovar-specific antigens might be responsible for the observed cross-reactive nature of the elicited immune response upon vaccination. Increased invasiveness of the Salmonella rfaH mutant into antigen-presenting cells, combined with increased intracellular killing and the potential for raising a cross-protective immune response, renders the rfaH mutant an ideal vaccine candidate.

Animals↗
PubMed1998

Identification and sequence analysis of a 27-kilobase chromosomal fragment containing a Salmonella pathogenicity island located at 92 minutes on the chromosome map of Salmonella enterica serovar typhimurium LT2.

Using a genomic approach, we have identified a new Salmonella pathogenicity island, SPI-4, which is the fourth Salmonella pathogenicity island to be identified. SPI-4 was located at 92 min on the chromosome map and was flanked by the ssb and soxSR loci. The DNA sequence covering the entire SPI-4 and both boundaries was determined. The size of SPI-4 was about 25 kb and it contains 18 putative open reading frames (ORFs). Three of these ORFs encode proteins that have significant homology with proteins involved in toxin secretion. Another five ORFs encode proteins that have significant homology with hypothetical proteins from Synechocystis sp. strain PCC6803 or Acinetobacter calcoaceticus. The rest of the ORFs encode novel proteins, one of which has five membrane-spanning domains. SPI-4 is likely to carry a type I secretion system involved in toxin secretion. Furthermore, a previously identified locus (ims98), which is required for intramacrophage survival, was also mapped within the SPI-4 region. These findings suggested that SPI-4 is needed for intramacrophage survival.

Amino Acid Sequence↗
PubMed1988

Central catecholaminergic system stimulates secretion of CRH at different sites.

To explore a possible differential role of distinct catecholamine (CA) innervation sites in corticotropin-releasing hormone (CRH) secretion, especially under stress conditions, we compared the effects in adult female rats of selective CA denervation of either the whole hypothalamus, by a discrete pharmacological lesion of the ventral noradrenergic ascending bundle [VNAB; 3 micrograms of 6-hydroxydopamine (6-OHDA) in 0.2 microliter of vehicle, bilaterally] or of the paraventricular nuclei (PVN) alone (1 microgram of 6-OHDA in 0.2 microliter of vehicle, bilaterally). Although both procedures induced a similar dramatic fall in norepinephrine and epinephrine concentrations (-55 to -65%) measured by high-performance liquid chromatography in PVN punches, the VNAB lesion, unlike PVN denervation, depleted the median eminence (ME) of both amines (-80%). Concomitantly, the VNAB lesion led to a 97% reduction of the immunoreactive (ir) CRH-41 concentration in the hypophysial portal vessels, associated with a 64% fall in plasma adrenocorticotropic hormone (ACTH), and, in another group, with an 80% inhibition of ether stress-induced ACTH surge. The deletion of CA innervation of the PVN alone reduced irCRH-41 levels in the portal vessels by only 57% and plasma ACTH by 35%. This lesion did not significantly impair stress-induced ACTH release. These results suggest that the CA innervation of the hypothalamus exerts a stimulatory control on CRH-41-secreting neurons not only directly at the perikaryal level but also at other hypothalamic sites of VNAB innervation including peripheral contacts between the terminals of CA and CRH nerves in the external ME.

Adrenocorticotropic Hormone↗
PubMed1998

Intrahypothalamic vasopressin release. An inhibitor of systemic vasopressin secretion?

Vasopressin and oxytocin are released into the extracellular space of the supraoptic (SON) and paraventricular nuclei (PVN). The dendrites of these neurones contain a high density of neurosecretory granules, and exocytotic profiles have been visualised by electron microscopy. Release within the SON has been measured using microperfusion techniques; release is tetrodotoxin-independent, calcium-dependent, and is activated by a range of physiological stimuli, including suckling, dehydration, haemorrhage and stress. Release of vasopressin into the SON is regulated by a number of forebrain and brainstem areas. Dendritic release does not necessarily parallel neurohypophyseal release, and may occur semi-independently of spike activity in the soma and axons. The physiological consequences of dendritic vasopressin release are not clear, vasopressin and oxytocin appear to induce further vasopressin and oxytocin release from the dendrites. In contrast, by combining retrodialysis and electrophysiology we have shown that, unlike oxytocin which excites oxytocin neurones, vasopressin inhibits the electrical activity of vasopressin neurones, and hence suppresses vasopressin release from the pituitary. Thus, vasopressin released from dendrites may act on vasopressin neurones to regulate their phasic activity by an auto-inhibitory action within the SON. Since dendritic vasopressin release is increased and prolonged after various stimuli, this mechanism may act to restrain excitation of vasopressin neurones (and hence vasopressin secretion from the neurohypophysis) during continuing stimulation.

Animals↗
PubMed1993

Inhibition of insulin secretion: a fail-safe system.

Insulin secretion from the beta-cells of the endocrine pancreas is subject to a pot-pourri of stimulatory, modulatory and inhibitory influences. beta-Cell secretion is reduced or blocked by a variety of inhibitors (including galanin, somatostatin and noradrenaline) which reach the cells either via the islet vascular system or are released locally from sympathetic and peptidergic nerves terminating in the pancreas. It is now becoming clear that among these many inhibitors, several have multiple mechanisms by which they inhibit release at the cellular level. Indeed, with multiple inhibitors (some of which are co-secreted) and multiple mechanisms of inhibition, the latter including a late effect in stimulus secretion coupling (perhaps on the exocytotic step per se), inhibition of insulin secretion has the characteristics of a fail-safe system.

Adenosine Triphosphate↗
PubMed1992

Endothelin acts at the subfornical organ to influence the activity of putative vasopressin and oxytocin-secreting neurons.

Systemic endothelin-1 (ET-1) enhances the activity of subfornical organ (SFO) neurons with identified projections to the paraventricular nucleus of the hypothalamus (PVN). The present electrophysiological experiments were undertaken to examine the mechanisms through which systemic ET influences vasopressin secretion. Systemic ET-1 (50-100 pmol) was found to influence the excitability of antidromically identified vasopressin and oxytocin-secreting neurons in the PVN or supraoptic nucleus (SON) of urethane-anaesthetized rats. Long-term stable recordings from 95 antidromically identified neurons showed 56% of putative vasopressin- (n = 41), and 37% of putative oxytocin- (n = 54) secreting neurons were activated by ET-1. Such effects normally demonstrated a short latency (less than 10 s), with a duration ranging between 10 and 300 s. In contrast, unidentified neurons in the vicinity of PVN and SON (n = 27) were unaffected by ET-1. The inability of peptides to cross the normal blood-brain barrier suggested that such effects of ET-1 result from actions of this peptide at the SFO which lacks this barrier and sends efferent neural projections to both SON and PVN. This hypothesis was tested by obtaining similar recordings from animals in which this structure was destroyed prior to experimentation. In these studies recordings from 15 putative vasopressin- and 29 putative oxytocin-secreting neurons showed that only 7% and 14%, respectively, were excited by systemic ET-1 in lesioned animals. These data show that increases in circulating levels of ET have predominantly excitatory effects on vasopressin- and oxytocin-secreting neurons in SON and PVN. The modified responsiveness of these neurons to ET-1 in SFO-lesioned animals suggests this as a likely CNS site at which this peptide acts within the central nervous system to elicit such effects.

Animals↗
PubMed1997

Evolution of arthropod silks.

Silks belong to the class of molecules called structural proteins. The ability to produce silk proteins has evolved multiple times in the arthropods, and silk secreting glands have evolved via two different pathways. The comparative data and phylogenetic analyses in this review suggest that the silk-secreting systems of spiders and insects are homologous and linked to the crural gland (origin of systemic pathway to silk production) and cuticular secretions (origin of surficial pathway to silk production) of an onychophoran-like ancestor. The evolution of silk secreting organs via a surficial pathway is possible in adult and larval hexapods, regardless of their developmental mode. Silk secretion via a systemic pathway is possible in either adult or larval hexapods, but only larval insects have dedicated silk producing glands. Spiders, however, have evolved silk producing systems via both systemic pathway and surficial pathways, and a single individual retains both throughout its lifespan. Early in the evolution of spiders, silk glands were undifferentiated, suggesting that the number of silk secreting glands of any individual was related to the spider's energetic need to produce large quantities of protein. However, the complex silk-producing systems that characterize the aerial web-building spiders and the diverse types of proteins they produce suggest that their silks reflect the diverse and increasing number of ways in which spiders use them. Because the muscular and innervated spinnerets and spigots of spiders allow them to control fiber functional properties, silk proteins represent an avenue through which animal behavior may directly affect the molecular properties of a protein.

Journal Article↗
PubMed2006

Terminal reassortment drives the quantum evolution of type III effectors in bacterial pathogens.

Many bacterial pathogens employ a type III secretion system to deliver type III secreted effectors (T3SEs) into host cells, where they interact directly with host substrates to modulate defense pathways and promote disease. This interaction creates intense selective pressures on these secreted effectors, necessitating rapid evolution to overcome host surveillance systems and defenses. Using computational and evolutionary approaches, we have identified numerous mosaic and truncated T3SEs among animal and plant pathogens. We propose that these secreted virulence genes have evolved through a shuffling process we have called "terminal reassortment." In terminal reassortment, existing T3SE termini are mobilized within the genome, creating random genetic fusions that result in chimeric genes. Up to 32% of T3SE families in species with relatively large and well-characterized T3SE repertoires show evidence of terminal reassortment, as compared to only 7% of non-T3SE families. Terminal reassortment may permit the near instantaneous evolution of new T3SEs and appears responsible for major modifications to effector activity and function. Because this process plays a more significant role in the evolution of T3SEs than non-effectors, it provides insight into the evolutionary origins of T3SEs and may also help explain the rapid emergence of new infectious agents.

Bacterial Proteins↗
PubMed1995

Development of a heterodimer plasmid system for the introduction of heterologous genes into streptococci.

We have previously constructed a model secretion system for oral streptococci using the secretory domain of the Streptococcus mutans GS-5 gtfB gene. As an initial step in developing systems for secreting protein fusions containing a glucan-binding polypeptide from streptococci, a DNA fragment corresponding to the glucan-binding domain (GBD) of the glucosyltransferase-S enzyme from strain GS-5 was fused to the gtfB secretory domain. However, it was not possible to clone the hybrid gene into Escherichia coli-streptococcal shuttle plasmids using E. coli as host cells. Integration of the hybrid GBD gene into the Streptococcus gordonii chromosome was directly accomplished utilizing a strategy involving a novel heterodimeric plasmid system. The heterodimer was constructed by ligating together two plasmids each containing DNA fragments homologous with a corresponding region of the S. gordonii chromosome flanking the hybrid GBD gene following a double crossover recombination event. However, this single-copy integrant secreted limited quantities of the GBD protein. In order to achieve high-level expression of the protein, the hybrid GBD gene was integrated into resident plasmids in S. gordonii following construction of intermediate heterodimeric plasmids. These plasmids contained the GBD gene flanked by sequences homologous to regions of the resident plasmids. The presence of the GBD protein in culture fluids from transformants harboring the multicopy plasmids demonstrated the secretion of the functional GBD protein. The strategy successfully developed for secreting the GBD in the streptococci should be adaptable for other organisms for which gene transfer systems are available. In addition, these systems will allow the direct introduction of genetic constructs when the constructs cannot be stably maintained in shuttle vectors within intermediate hosts such as E. coli.

Binding Sites↗