A Novel Spore Protein,ExsM, Regulates Formation of the Exosporium in Bacillus cereus and Bacillus anthracis and Affects Spore Size and Shape

Bacillus cereus spores are assembled with a series of concentric layers that protect them from a wide range of environmental stresses. The outermost layer, or exosporium, is a bag-like structure that interacts with the environment and is composed of more than 20 proteins and glycoproteins. Here, we identified a new spore protein, ExsM, from a β-mercaptoethanol extract of B. cereus ATCC 4342 spores. Subcellular localization of an ExsM-green fluorescent protein (GFP) protein revealed a dynamic pattern of fluorescence that follows the site of formation of the exosporium around the forespore. Under scanning electron microscopy, exsM null mutant spores were smaller and rounder than wild-type spores, which had an extended exosporium (spore length for the wt, 2.40 ± 0.56 μm, versus that for the exsM mutant, 1.66 ± 0.38 μm [P < 0.001]). Thin-section electron microscopy revealed that exsM mutant spores were encased by a double-layer exosporium, both layers of which were composed of a basal layer and a hair-like nap. Mutant exsM spores were more resistant to lysozyme treatment and germinated with higher efficiency than wild-type spores, and they had a delay in outgrowth. Insertional mutagenesis of exsM in Bacillus anthracis ΔSterne resulted in a partial second exosporium and in smaller spores. In all, these findings suggest that ExsM plays a critical role in the formation of the exosporium.Bacillus cereus and Bacillus anthracis are closely related members of the Bacillus cereus group (47). Although B. cereus is mainly an apathogenic organism, certain isolates can cause two different types of food poisoning, emetic syndrome and diarrheal disease (18). The emetic syndrome is caused by ingestion of cereulide, a heat-resistant toxin produced by vegetative cells contaminating the food (30), while the diarrheal disease occurs when spores germinate in the intestinal tract. Spores are also the infective agent in anthrax, a disease caused by B. anthracis (64).B. cereus and B. anthracis differentiate into spores when faced with nutrient deprivation. The spore is a dormant cell type that can remain viable for decades until favorable conditions induce germination and the resumption of vegetative growth. The remarkable resistance properties of the spore result from its unique architecture, consisting of a series of concentric protective layers (51). The spore core contains the genetic material and is surrounded by the cortex, a thick layer of modified peptidoglycan that promotes a highly dehydrated state. Encasing the core and the cortex, the coat is a multilayer protein shell that provides mechanical and chemical resistance. In addition, both the cortex and coat contribute to spore germination (17). Separated from the coat by an interspace, the exosporium encloses the rest of the spore, and it is composed of an inner basal layer and an outer hair-like nap (25).Being the most external layer of the spore, the exosporium interacts directly with the environment and as such provides a semipermeable barrier that may exclude large molecules, like antibodies and hydrolytic enzymes (3, 23, 24, 54). However, the exosporium does not appear to contribute to the typical resistance properties of the spore (6, 35, 60). Also, the exosporium is not necessary in anthrax pathogenesis when tested under laboratory conditions (7, 27, 59), although it is able to down-modulate the innate immune response to spores and mediate adhesion to host tissues (4, 8, 43, 44). The exosporium may also help the spore avoid premature germination in unsustainable environments, since it contains two enzymes, alanine racemase (Alr) and inosine hydrolase (Iunh), that can inactivate low quantities of the germinants l-alanine and inosine, respectively (6, 48, 55, 61). However, regulation of germination by the exosporium is poorly understood. Mutation of exosporial proteins has resulted in only negligible and inconsistent germination phenotypes (2, 5, 27, 28, 52, 54).The exosporium is composed of at least 20 proteins and glycoproteins in tight or loose association (48, 53, 57, 61, 65). These proteins are synthesized in the mother cell and always start self-assembly at the forespore pole near the middle of the mother cell, concurrently with the cortex and coat formation (42). Exosporium assembly is discontinuous and starts with a synthesis of a substructure known as the cap, which likely contains only a subset of the proteins present in the exosporium (55). After cap formation, construction of the rest of the exosporium requires the expression of ExsY (6). BclA is the main component of the hair-like nap on the external side of the exosporium, and it is linked to the basal layer through interaction with ExsFA/BxpB (54, 58). In addition, CotE participates in the correct attachment of the exosporium to the spore (27).Despite these findings, exosporium assembly continues to be a poorly understood process, and many questions remain regarding its composition and the regulation of its synthesis. In this study, we characterized a new spore protein, ExsM, which plays a key role in assembly of the exosporium. In B. cereus, inactivation of exsM resulted in spores with an unusual double-layer exosporium, and a similar phenotype was also observed in B. anthracis exsM null mutant spores. Finally, double-layer exosporium spores allowed us to study the role of the exosporium in germination and outgrowth.     

Age-related infection and transmission patterns of human cysticercosis

Neurocysticercosis is recognised as an important but neglected cause of epilepsy in developing countries where the parasite occurs. Data on the transmission dynamics of the parasite in endemic areas are scarce. Individuals living in these areas are likely to be highly exposed to the parasite, but relatively few of them develop active infections. The present study aimed to describe and gain insights into changes in antibody responses and infection patterns related to age and/or gender in a south Ecuadorian rural population by combining antibody and antigen serological data with demographic characteristics. In 25% of the population, antibodies to Taenia solium cysticerci were detected whilst 2.9% had circulating parasite antigens. The proportion of antibody-positive individuals increased significantly until the age of 40 years to become stable in older individuals. A rule-based simulation model was developed to explain these variations and to reflect the dynamics of exposure to, and transmission of, the parasite. In contrast, the proportion of people presenting circulating parasite antigens, reflecting an active infection, was significantly higher in people older than 60 years. Immunosenescence could explain such an observation since a weaker immune system in the elderly would facilitate the establishment and maintenance of viable cysticerci compared with fully immunocompetent younger individuals. This work points out the role of the immune system in the development of cysticercosis within an exposed population and highlights new essential issues in understanding the transmission dynamics of the parasite, its incidence and the resulting immunological response at a population level.     

Neospora caninum: Cloning and expression of a gene coding for cytokine-inducing profilin

Profilins are actin-binding proteins that in Toxoplasma gondii stimulate innate immunity in mice by binding Toll-like receptors (TLR) on dendritic cells (DC) leading to release of inflammatory cytokines, primarily IL-12 and IFN-γ. The purpose of the present study was to characterize Neospora caninum profilin, termed NcProfilin. Recombinant NcProfilin was purified by affinity chromatography, and used to prepare specific antisera to allow characterization of native NcProfilin antigen in N. caninum tachyzoites. By immunoblotting, recombinant NcProfilin is 22 kDa, and is similar in size to the respective 22 kDa native protein. Immunofluorescence and immunoelectron microscopy localized native NcProfilin to the apical end of N. caninum tachyzoites. Incubation of recombinant NcProfilin with spleen cells from BALB/c mice induced release of IFN-γ. Also, injection of BALB/c mice with purified rNcProfilin elicited a strong IFN-γ and IL-12 responses at 6 and 24 h after injection indicating that NcProfilin may be an important protein in regulation of cytokine responses to N. caninum.     

Comparing system-specific chaperone interactions with their Tat dependent redox enzyme substrates

Redox enzyme substrates of the twin-arginine translocation (Tat) system contain a RR-motif in their leader peptide and require the assistance of chaperones, redox enzyme maturation proteins (REMPs). Here various regions of the RR-containing oxidoreductase subunit (leader peptide, full preprotein with and without a leader cleavage site, mature protein) were assayed for interaction with their REMPs. All REMPs bound their preprotein substrates independent of the cleavage site. Some showed binding to either the leader or mature region, whereas in one case only the preprotein bound its REMP. The absence of Tat also influenced the amount of chaperone-substrate interaction.

Structured summary

MINT-8047497: FdhE (uniprotkb:P13024) and FdoG (uniprotkb:P32176) physically interact (MI:0915) by two hybrid (MI:0018)MINT-8046441: HybO (uniprotkb:P69741) and HybE (uniprotkb:P0AAN1) physically interact (MI:0915) by two hybrid (MI:0018)MINT-8046375: DmsA (uniprotkb:P18775) and DmsD (uniprotkb:P69853) physically interact (MI:0915) by two hybrid (MI:0018)MINT-8046425: TorA (uniprotkb:P33225) and TorD (uniprotkb:P36662) physically interact (MI:0915) by two hybrid (MI:0018)MINT-8046393: NarJ (uniprotkb:P0AF26) and NarG (uniprotkb:P09152) physically interact (MI:0915) by two hybrid (MI:0018)MINT-8046409: NapD (uniprotkb:P0A9I5) and NapA (uniprotkb:P33937) physically interact (MI:0915) by two hybrid (MI:0018)     

A preliminary study on the function of food begging in Sichuan snub-nosed monkeys (Rhinopithecus roxellana): challenge to begging for nutritional gain

Several hypotheses have been developed to explain what benefits a donor may gain from sharing food with another individual, with nutritional gain assumed to be the sole benefit for the beggar. Recently, it has been proposed that begging behaviour serves a social function in non-human primates. In this study, the nutritional-gain assumption was again challenged based on observations on a captive group of Sichuan snub-nosed monkeys (Rhinopithecus roxellana), or golden snub-nosed monkeys. The major findings from this study are that (1) beggars sometimes left their own branches or passed by available branches to beg for similar food from other individuals, (2) beggars occasionally ignored branches that were acquired by begging and (3) food begging occurred more frequently in the all-male unit after the social rank had changed between 2 individuals in this unit. Overall, these preliminary findings suggest that some begging behaviours in captive golden snub-nosed monkeys were not driven by nutritional gain only; instead, we propose that these begging behaviours could be interpreted as attempts at deriving social benefits.     

Novel Mechanisms in the Regulation of G Protein-coupled Receptor Trafficking to the Plasma Membrane

β₂-Adrenergic receptors (β₂-AR) are low abundance, integral membrane proteins that mediate the effects of catecholamines at the cell surface. Whereas the processes governing desensitization of activated β₂-ARs and their subsequent removal from the cell surface have been characterized in considerable detail, little is known about the mechanisms controlling trafficking of neo-synthesized receptors to the cell surface. Since the discovery of the signal peptide, the targeting of the integral membrane proteins to plasma membrane has been thought to be determined by structural features of the amino acid sequence alone. Here we report that localization of translationally silenced β₂-AR mRNA to the peripheral cytoplasmic regions is critical for receptor localization to the plasma membrane. β₂-AR mRNA is recognized by the nucleocytoplasmic shuttling RNA-binding protein HuR, which silences translational initiation while chaperoning the mRNA-protein complex to the cell periphery. When HuR expression is down-regulated, β₂-AR mRNA translation is initiated prematurely in perinuclear polyribosomes, leading to overproduction of receptors but defective trafficking to the plasma membrane. Our results underscore the importance of the spatiotemporal relationship between β₂-AR mRNA localization, translation, and trafficking to the plasma membrane, and establish a novel mechanism whereby G protein-coupled receptor (GPCR) responsiveness is regulated by RNA-based signals.     

Potassium Channel Modulation by a Toxin Domain in Matrix Metalloprotease 23

Peptide toxins found in a wide array of venoms block K⁺ channels, causing profound physiological and pathological effects. Here we describe the first functional K⁺ channel-blocking toxin domain in a mammalian protein. MMP23 (matrix metalloprotease 23) contains a domain (MMP23_TxD) that is evolutionarily related to peptide toxins from sea anemones. MMP23_TxD shows close structural similarity to the sea anemone toxins BgK and ShK. Moreover, this domain blocks K⁺ channels in the nanomolar to low micromolar range (Kv1.6 > Kv1.3 > Kv1.1 = Kv3.2 > Kv1.4, in decreasing order of potency) while sparing other K⁺ channels (Kv1.2, Kv1.5, Kv1.7, and KCa3.1). Full-length MMP23 suppresses K⁺ channels by co-localizing with and trapping MMP23_TxD-sensitive channels in the ER. Our results provide clues to the structure and function of the vast family of proteins that contain domains related to sea anemone toxins. Evolutionary pressure to maintain a channel-modulatory function may contribute to the conservation of this domain throughout the plant and animal kingdoms.     

Poly(ADP-ribose) polymerase-1 hyperactivation and impairment of mitochondrial respiratory chain complex I function in reperfused mouse hearts

Poly(ADP-ribose) polymerase-1 (PARP-1), the most abundant member of the PARP family, is a nuclear enzyme that catalyzes ADP-ribose transfer from NAD+ to specific acceptor proteins in response to DNA damage. Excessive PARP-1 activation is an important cause of infarction and contractile dysfunction in heart tissue during interruptions of blood flow. The mechanisms by which PARP-1 inhibition and disruption dramatically improve metabolic recovery and reduce oxidative stress during cardiac reperfusion have not been fully explored. We developed a mouse heart experimental protocol to test the hypothesis that mitochondrial respiratory complex I is a downstream mediator of beneficial effects of PARP-1 inhibition or disruption. Pharmacological inhibition of PARP-1 activity produced no deterioration of hemodynamic function in C57BL/6 mouse hearts. Hearts from PARP-1 knockout mice also exhibited normal baseline contractility. Prolonged ischemia-reperfusion produced a selective defect in complex I function distal to the NADH dehydrogenase component. PARP-1 inhibition and PARP-1 gene disruption conferred equivalent protection against mitochondrial complex I injury and were strongly associated with improvement in myocardial energetics, contractility, and tissue viability. Interestingly, ischemic preconditioning abolished cardioprotection stimulated by PARP-1 gene disruption. Treatment with the antioxidant N-(2-mercaptopropionyl)-glycine or xanthine oxidase inhibitor allopurinol restored the function of preconditioned PARP-1 knockout hearts. This investigation establishes a strong association between PARP-1 hyperactivity and mitochondrial complex I dysfunction in cardiac myocytes. Our findings advance understanding of metabolic regulation in myocardium and identify potential therapeutic targets for prevention and treatment of ischemic heart disease.     

HO-2 provides endogenous protection against oxidative stress and apoptosis caused by TNF-alpha in cerebral vascular endothelial cells

Tumor necrosis factor- (TNF-) causes oxidative stress and apoptosis in a variety of cell types. Heme oxygenase (HO) degrades heme to bilirubin, an antioxidant, and carbon monoxide (CO), a cell cycle modulator, and a vasodilator. Newborn pig cerebral microvascular endothelial cells (CMVEC) highly express constitutive HO-2. We investigated the role of HO-2 in protection against TNF--induced apoptosis in cerebral vascular endothelium. In CMVEC from mice and newborn pigs, 15 ng/ml TNF- alone, or with 10 µg/ml cycloheximide (CHX) caused apoptosis detected by nuclear translocation of p65 NF-B, caspase-3 activation, DNA fragmentation, cell-cell contact destabilization, and cell detachment. TNF- did not induce HO-1 expression in CMVEC. CMVEC from HO-2 knockout mice showed greater sensitivity to apoptosis caused by serum deprivation and TNF- than did wild-type mice. TNF- increased reactive oxygen species generation, including hydrogen peroxide and superoxide radicals, as detected by dihydrorhodamine-123 and dihydroethidium. The TNF- response was inhibited by superoxide dismutase and catalase suggesting apoptosis is oxidative stress related. Inhibition of endogenous HO-2 in newborn pig CMVEC increased oxidative stress and exaggerated apoptosis caused by serum deprivation and TNF-. In HO-1-overexpressing CMVEC (HO-1 selective induction by cobalt portophyrin), TNF- did not cause apoptosis. A CO-releasing compound, CORM-A1, and bilirubin blocked TNF--induced reactive oxygen species accumulation and apoptosis consistent with the antioxidant and antiapoptotic roles of the end products of HO activity. We conclude that HO-2 is critical for protection of cerebrovascular endothelium against apoptotic changes induced by oxidative stress and cytokine-mediated inflammation. carbon monoxide; bilirubin; vascular injury; reactive oxygen species; heme oxygenase; cycloheximide     

Dependence of acetylcholine and ADP dilation of pial arterioles on heme oxygenase after transfusion of cell-free polymeric hemoglobin

Polymers of cell-free hemoglobin have been designed for clinical use as oxygen carriers, but limited information is available regarding their effects on vascular regulation. We tested the hypothesis that the contribution of heme oxygenase (HO) to acetylcholine-evoked dilation of pial arterioles is upregulated 2 days after polymeric hemoglobin transfusion. Dilator responses to acetylcholine measured by intravital microscopy in anesthetized cats were blocked by superfusion of the HO inhibitor tin protoporphyrin-IX (SnPPIX) in a group that had undergone exchange transfusion with hemoglobin 2 days earlier but not in surgical sham and albumin-transfused groups. However, immunoblots from cortical brain homogenates did not reveal changes in expression of the inducible isoform HO1 or the constitutive isoform HO2 in the hemoglobin-transfused group. To test whether the inhibitory effect of SnPPIX was present acutely after hemoglobin transfusion, responses were measured within an hour of completion of the exchange transfusion. In control and albumin-transfused groups, acetylcholine responses were unaffected by SnPPIX but were blocked by addition of the nitric oxide synthase inhibitor N(omega)-nitro-l-arginine (l-NNA) to the superfusate. In hemoglobin-transfused groups, the acetylcholine response was blocked by either SnPPIX or l-NNA alone. The effect of another HO inhibitor, chromium mesoporphyrin (CrMP), was tested on ADP, another endothelial-dependent dilator, in anesthetized rats. Pial arteriolar dilation to ADP was unaffected by CrMP in controls but was attenuated 62% by CrMP in rats transfused with hemoglobin. It is concluded that 1) polymeric hemoglobin transfusion acutely upregulates the contribution of HO to acetylcholine-induced dilation of pial arterioles in cats, 2) this upregulation persists 2 days after transfusion when 95% of the hemoglobin is cleared from the circulation, and 3) this acute upregulation of HO signaling is ubiquitous in that similar effects were observed with a different endothelial-dependent agonist (i.e., ADP) in a another species (rat).