Axisymmetry of critical points for the Onsager functional

A simple proof is given of the classical result (Fatkullin I, Slastikov V. 2005 Critical points of the Onsager functional on a sphere. Nonlinearity 18, 2565-2580 (doi:10.1088/0951-7715/18/6/008); Liu H et al. 2005 Axial symmetry and classification of stationary solutions of Doi-Onsager equation on the sphere with Maier-Saupe potential. Commun. Math. Sci. 3, 201-218 (doi:10.4310/CMS.2005.v3.n2.a7)) that critical points for the Onsager functional with the Maier-Saupe molecular interaction are axisymmetric, including the case of stable critical points with an additional dipole-dipole interaction (Zhou H et al. 2007 Characterization of stable kinetic equilibria of rigid, dipolar rod ensembles for coupled dipole-dipole and Maier-Saupe potentials. Nonlinearity 20, 277-297 (doi:10.1088/0951-7715/20/2/003)). The proof avoids spherical polar coordinates, instead using an integral identity on the sphere S². For general interactions with absolutely continuous kernels the smoothness of all critical points is established, generalizing a result in (Vollmer MAC. 2017 Critical points and bifurcations of the three-dimensional Onsager model for liquid crystals. Archive for Rational Mechanics and Analysis 226, 851-922 (doi:10.1007/s00205-017-1146-8)) for the Onsager interaction. It is also shown that non-axisymmetric critical points exist for a wide variety of interactions including that of Onsager. This article is part of the theme issue 'Topics in mathematical design of complex materials'.

Role of sensory input distribution and intrinsic connectivity in lateral amygdala during auditory fear conditioning: a computational study

We propose a novel reduced-order neuronal network modeling framework that includes an enhanced firing rate model and a corresponding synaptic calcium-based synaptic learning rule. Specifically, we propose enhancements to the Wilson-Cowan firing-rate neuron model that permit full spike-frequency adaptation seen in biological lateral amygdala (LA) neurons, while being sufficiently general to accommodate other spike-frequency patterns. We also report a technique to incorporate calcium-dependent plasticity in the synapses of the network using a regression scheme to link firing rate to postsynaptic calcium. Together, the single-cell model and the synaptic learning scheme constitute a general framework to develop computationally efficient neuronal networks that employ biologically realistic synaptic learning. The reduced-order modeling framework was validated using a previously reported biophysical conductance-based neuronal network model of a rodent LA that modeled features of Pavlovian conditioning and extinction of auditory fear (Li et al., 2009). The framework was then used to develop a larger LA network model to investigate the roles of tone and shock distributions and of intrinsic connectivity in auditory fear learning. The model suggested combinations of tone and shock densities that would provide experimental estimates of tone responsive and conditioned cell proportions. Furthermore, it provided several insights including how intrinsic connectivity might help distribute sensory inputs to produce conditioned responses in cells that do not directly receive both tone and shock inputs, and how a balance between potentiation of excitation and inhibition prevents stimulus generalization during fear learning.

Spinal extension exercises prevent natural progression of kyphosis

The angle of kyphosis increases with age with the most rapid increase occurring between 50 and 60 years. The progression of kyphosis was prevented in women ages 50-59 years who performed extension exercises three times a week for one year.

INTRODUCTION

The purpose of this study was to (1) measure the progression of the angle of kyphosis with age and (2) determine whether spinal extension exercises prevent progression of hyperkyphosis in women 50-59 years of age.

METHOD

Part 1: Cross-sectional study of changes in posture with age, determined by measuring spinal curves in 250 women 30-79 years of age. Part 2: One-year prospective, descriptive analysis of the effect of extension exercises on posture in women 50-59 years of age. Depth of the cervical curve (CD), area under the thoracic curve (TA), and height were measured using a device developed at Kansas University Medical Center. Changes in CD and TA in women compliant with extension exercises were compared to those in non-compliant women.

RESULTS

Kyphosis increases with age in healthy women, with the greatest difference observed between women 50 and 59 years of age. The progression of kyphosis was greater in women who did not perform extension exercises compared to those who performed extension exercises three times per week for 1 year. The difference in change in CD and TA between the two groups was highly significant (CD p = .0001, TA p = .0001).

CONCLUSIONS

Kyphosis increases with age in healthy women. In this study the greatest difference in the angle of kyphosis was observed between the fifth and sixth decade. Exercises which strengthen the extensor muscles of the spine can delay the progression of hyperkyphosis in the group included in this study, i.e., women 50-59 years of age.

The role of zinc and metallothionein in the dextran sulfate sodium-induced colitis mouse model

Zinc (Zn) and its binding protein metallothionein (MT) have been proposed to suppress the disease activity in ulcerative colitis. To determine the role of Zn and MT in the dextran sulfate sodium (DSS)-induced model of colitis in mice, a DSS dose-response study was conducted in male C57BL/6 wild-type (MT+/+) and MT-null (MT-/-) mice by supplementing 2%, 3%, and 4% DSS in the drinking water for 6 days. In the intervention study, colitis was induced with 2% DSS, Zn (24 mg/ml as ZnO) was gavaged (0.1 ml) daily, concurrent with DSS administration, and the disease activity index (DAI) was scored daily. Histology, MT levels, and myeloperoxidase (MPO) activity were determined. DAI was increased (P<0.05) by 16% and 21% with 3% and 4% concentrations of DSS, respectively, compared to 2%, evident after 5 days of DSS administration. MPO activity was increased in MT+/+ compared to MT-/- mice and those receiving DSS. Zn administration had a 50% (P<0.05) lower DAI compared to DSS alone. Zn partially prevented the distal colon of MT+/+ by 47% from DSS-induced damage compared to MT-/- mice. MT did not prevent DSS-induced colitis and Zn was partially effective in amelioration of DSS-induced colitis.

Differential effects of virulent and avirulent equine infectious anemia virus on macrophage cytokine expression

Equine infectious anemia virus (EIAV) causes rapid development of acute disease followed by recurring episodes of fever, thrombocytopenia, and viremia. Most infected equid eventually bring the virus under immunological control. We recently reported the development of an equine-specific ribonuclease protection assay (RPA) to quantitate mRNA levels of 10 cytokines. Using this newly developed RPA, we now show significant differences in cytokine induction in equine monocyte-derived macrophages (EMDM) exposed to virulent and avirulent EIAV. Virulent EIAV17 induced significant increases in interleukin (IL)-1alpha, IL-1beta, IL-6, IL-10, and tumor necrosis factor (TNF)-alpha by 0.5-1 h postinfection (hpi). In contrast, the avirulent virus failed to induce any of the tested cytokines above that of control levels. These data show a direct correlation between cytokine dysregulation and EIAV pathogenesis.

SU proteins from virulent and avirulent EIAV demonstrate distinct biological properties

Biologic activity of equine infectious anemia virus (EIAV) surface (SU) glycoprotein was assayed in a mouse model. Recombinant SU from virulent EIAV17 (SU17), administered intraperitoneally to mouse pups, induced dose-dependent diarrheal responses similar to those reported for SIV SU (Virology 277 (2000) 250). SU17 caused fluid accumulation without histological lesions in mouse intestinal loops, induced chloride secretory currents in Ussing chambers and increased inositol 1,4,5 triphosphate (IP3) levels in HT29 cells. An SU17 peptide, SU17(299-330), provoked a dose-dependent diarrheal response akin to enterotoxic peptides from SIV. In contrast, SU from an avirulent EIAV strain failed to induce a dose response in mouse pups and produced lower levels of activity than SU17 in Ussing chambers and IP3 assays. These results demonstrate that a mouse pup model is useful to monitor EIAV SU biologic activity, showing clear differences between the activities of SU derived from virulent and avirulent viruses, and may provide a useful screen of EIAV virulence.

Comparison of SIVmac239(352-382) and SIVsmmPBj41(360-390) enterotoxic synthetic peptides

To characterize the active domain of the simian immunodeficiency virus (SIV) surface unit (SU) enterotoxin, peptides corresponding to the V3 loop of SIVmac239 (SIVmac) and SIVsmmPBj41 (SIVpbj) were synthesized and examined for enterotoxic activity, alpha-helical structure, and interaction(s) with model membranes. SIVmac and SIVpbj induced a dose-dependent diarrhea in 6-8-day-old mouse pups similar to full-length SU. The peptides mobilized [Ca(2+)](i) in HT-29 cells with distinct oscillations and elevated inositol triphosphate levels. Circular dichroism analyses showed the peptides were predominantly random coil in buffer, but increased in alpha-helical content when placed in a hydrophobic environment or with cholesterol-containing membrane vesicles that are rich in anionic phospholipids. None of the peptides underwent significant secondary structural changes in the presence of neutral vesicles indicating ionic interactions were important. These data show that the SIV SU enterotoxic domain localizes in part to the V3 loop region and interacts with anionic membrane domains on the host cell surface.

The dissolution of organic solvents from Amerlock 400 epoxy paint

The dissolution of organic solvents from containment coatings into the sump water is expected to be a key rate-controlling process, influencing the pH, the steady-state water radiolysis product concentration, and the formation of organic iodides in containment following a postulated reactor accident. The dissolution process is therefore an important component in modelling iodine behaviour in post-accident containment. The rate of release of ethyl benzene and m- and o-xylene from Amerlock 400 epoxy paint in contact with water has been measured. The release rate was found to be comparable to the release rate of methyl isobutyl ketone from various polyurethane, vinyl, and epoxy paints. The pseudo-first-order rate constant for dissolution of the solvents from these containment coatings is dependent only upon paint thickness and temperature, whereas the total amount of solvent released depends upon paint thickness. The solvent-release process is governed by the rate of uptake of water by the coupons, a Fickian diffusion-controlled process.Key words: dissolution, kinetics, organic solvents, paint.

Temporal changes in cytokine expression of foals during the first month of life

Foals are uniquely susceptible to a wide variety of opportunistic infections normally associated with immunodeficiencies. Little is understood about the immune system of foals during the neonatal period. An apparent age-related susceptibility predisposes neonatal foals to infectious diseases and hinders therapeutic and preventative interventions for these diseases. Cytokine expression is correlated with the type of immune response as well as the severity of a disease. In this study, we measured foal peripheral blood mononuclear cell (PBMC)-specific mRNA cytokine expression from 72 foals from three different farms during the first 4 weeks of life. Interleukin-1alpha (IL-1alpha), IL-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p35, IL-12p40, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-beta1 (TGF-beta1) were cloned and transcribed in vitro to generate antisense probes for ribonuclease protection assays. Using linear mixed-effect models, we determined that IFN-gamma, TGF-beta1, and IL-1alpha increased significantly (P<0.05) with age.

Simultaneous quantitation of equine cytokine mRNAs using a multi-probe ribonuclease protection assay

A rapid multi-probe ribonuclease protection assay (RPA) was developed to quantitate equine-specific cytokine mRNA levels in activated equine monocyte-derived macrophages (EMDM) and equine peripheral blood mononuclear cells (EPBMC). Eleven template plasmids specific to 10 equine cytokine genes and the beta-actin gene were generated from which radiolabeled anti-sense RNA probes were produced. The multi-probe RPA simultaneously quantitated mRNA levels of equine IL-1alpha, IL-1beta, IL-6, IL-8, IL-10, IL-12 p35, IL-12 p40, IFN-gamma, TGF-1beta and TNF-alpha in EPBMC and EMDM with coefficients of variation as low as 0.03-0.08 (3-8%) when normalized to beta-actin expression. This sensitive and rapid assay provides a valuable tool for studies of equine immune responses.

Recombinant Norwalk virus-like particles administered intranasally to mice induce systemic and mucosal (fecal and vaginal) immune responses

Recombinant Norwalk virus-like particles (rNV VLPs) were administered to BALB/c mice by the intranasal (i.n.) route to evaluate the induction of mucosal antibody responses. The results were compared to systemic and mucosal responses observed in new and previous studies (J. M. Ball, M. E. Hardy, R. L. Atmar, M. E. Connor, and M. K. Estes, J. Virol. 72:1345-1353, 1998) after oral administration of rNV VLPs. Immunizations were given in the presence or absence of a mucosal adjuvant, mutant Escherichia coli heat-labile toxin LT(R192G). rNV-specific immunoglobulin G (IgG) and fecal IgA were evaluated by enzyme-linked immunosorbent assay. The i.n. delivery of rNV VLPs was more effective than the oral route at inducing serum IgG and fecal IgA responses to low doses of rNV particles. Vaginal responses of female mice given VLPs by the i.n. and oral routes were also examined. All mice that received two immunizations with low doses i.n. (10 or 25 microg) of rNV VLPs and the majority of mice that received two high doses orally (200 microg) in the absence of adjuvant had rNV-specific serum IgG, fecal, and vaginal responses. Additional experiments evaluated whether rNV VLPs can function as a mucosal adjuvant by evaluating the immune responses to two soluble proteins, keyhole limpet hemocyanin and chicken egg albumin. Under the conditions tested, rNV VLPs did not enhance the serum IgG or fecal IgA response to these soluble proteins when coadministered by the i.n. or oral route. Low doses of nonreplicating rNV VLPs are immunogenic when administered i.n. in the absence of adjuvant, and addition of adjuvant enhanced the magnitude and duration of these responses. Recombinant NV VLPs represent a candidate mucosal vaccine for NV infections in humans.

Membrane interactions of a novel viral enterotoxin: rotavirus nonstructural glycoprotein NSP4

The rotavirus enterotoxin, NSP4, is a novel secretory agonist that also plays a role in the unique rotavirus morphogenesis that involves a transient budding of newly made immature viral particles into the endoplasmic reticulum. NSP4 and an active peptide corresponding to NSP4 residues 114 to 135 (NSP4(114-135)) mobilize intracellular calcium and induce secretory chloride currents when added exogenously to intestinal cells or mucosa. Membrane-NSP4 interactions may contribute to these alterations; however, details of a lipid-binding domain are unresolved. Therefore, circular dichroism was used to determine (i) the interaction(s) of NSP4 and NSP4(114-135) with model membranes, (ii) the conformational changes elicited in NSP4 upon interacting with membranes, (iii) if NSP4(114-135) is a membrane interacting domain, and (iv) the molar dissociation constant (K(d)) of NSP4(114-135) with defined lipid vesicles. Circular dichroism revealed for the first time that NSP4 and NSP4(114-135) undergo secondary structural changes upon interaction with membrane vesicles. This interaction was highly dependent on both the membrane surface curvature and the lipid composition. NSP4 and NSP4(114-135) preferentially interacted with highly curved, small unilamellar vesicle membranes (SUV), but significantly less with low-curvature, large unilamellar vesicle membranes (LUV). Binding to SUV, but not LUV, was greatly enhanced by negatively charged phospholipids. Increasing the SUV cholesterol content, concomitant with the presence of negatively charged phospholipids, further potentiated the interaction of NSP4(114-135) with the SUV membrane. The K(d) of NSP4(114-135) was determined as well as partitioning of NSP4(114-135) with SUVs in a filtration-binding assay. These data confirmed NSP4 and its active peptide interact with model membranes that mimic caveolae.

The reduction of I2 by H2O2 in aqueous solution

The reduction of I2 by hydrogen peroxide, a primary water radiolysis product, has been identified as a key reaction that would influence iodine volatility in nuclear reactor accident conditions (1–3). Although there have been a number of studies of the reduction of I2, there exists a great degree of controversy regarding the intermediates involved, the effect of buffers, and the general rate law (1–9). Because the rates and the mechanism of this reaction are important in predicting the pH dependence of iodine behaviour in reactor containment building after a postulated reactor accident, we have undertaken a kinetic study of I2 reduction by H2O2 in aqueous solution over a pH range of 6–9. The experiments were performed using stopped-flow instrumentation and monitoring the decay of I–3 spectrophotometrically. The effects of buffer catalysis have been examined by comparison of kinetic data obtained in sodium barbital (5,5-diethylbarbituric acid), disodium citrate, and disodium hydrogen phosphate buffers. The effect of buffers, combined with the complex acid dependence of the rate law, explains many of the discrepancies reported in earlier literature.Key words: hydrogen peroxide, molecular iodine, kinetics, iodine volatility.

The envelope glycoprotein of simian immunodeficiency virus contains an enterotoxin domain

By the use of a mouse model, the enteropathic effects of the simian immunodeficiency virus (SIV) surface unit (SU) envelope glycoprotein were explored. Purified SU (0.01-0.45 nmol) was administered intraperitoneally to 6- to 8-day-old mouse pups and induced a dose-dependent diarrheal response. Surgical introduction of SU into adult mouse intestinal loops revealed fluid accumulation without histological alterations and SU-treated unstripped intestinal mucosa induced chloride (Cl(-)) secretory currents in Ussing chambers. Similarly to rotavirus NSP4, the first described viral enterotoxin, SU induced a transient increase in intracellular calcium levels and increased inositol 1,4,5-triphosphate (IP(3)) levels in HT-29 cells. These data indicate the calcium response is mediated by IP(3). The presence of diarrhea and fluid accumulation within intestinal loops in the absence of histological alterations and induction of Cl(-) secretory currents demonstrate that SIV contains an enterotoxic domain localized within SU and is the second viral enterotoxin described.

Direct inhibitory effect of rotavirus NSP4(114-135) peptide on the Na(+)-D-glucose symporter of rabbit intestinal brush border membrane

The direct effect of a rotavirus nonstructural glycoprotein, NSP4, and certain related peptides on the sodium-coupled transport of D-glucose and of L-leucine was studied by using intestinal brush border membrane vesicles isolated from young rabbits. Kinetic analyses revealed that the NSP4(114-135) peptide, which causes diarrhea in young rodents, is a specific, fully noncompetitive inhibitor of the Na(+)-D-glucose symporter (SGLT1). This interaction involves three peptide-binding sites per carrier unit. In contrast, the Norwalk virus NV(464-483) and mNSP4(131K) peptides, neither of which causes diarrhea, both behave inertly. The NSP4(114-135) and NV(464-483) peptides inhibited Na(+)-L-leucine symport about equally and partially via a different transport mechanism, in that Na(+) behaves as a nonobligatory activator. The selective and strong inhibition caused by the NSP4(114-135) peptide on SGLT1 in vitro suggests that during rotavirus infection in vivo, NSP4 can be one effector directly causing SGLT1 inhibition. This effect, implying a concomitant inhibition of water reabsorption, is postulated to play a mechanistic role in the pathogenesis of rotavirus diarrhea.

Norwalk virus open reading frame 3 encodes a minor structural protein

Norwalk virus (NV) is a causative agent of acute epidemic nonbacterial gastroenteritis in humans. The inability to cultivate NV has required the use of molecular techniques to examine the genome organization and functions of the viral proteins. The function of the NV protein encoded by open reading frame 3 (ORF 3) has been unknown. In this paper, we report the characterization of the NV ORF 3 protein expressed in a cell-free translation system and in insect cells and show its association with recombinant virus-like particles (VLPs) and NV virions. Expression of the ORF 3 coding region in rabbit reticulocyte lysates resulted in the production of a single protein with an apparent molecular weight of 23,000 (23K protein), which is not modified by N-linked glycosylation. The ORF 3 protein was expressed in insect cells by using two different baculovirus recombinants; one recombinant contained the entire 3' end of the genome beginning with the ORF 2 coding sequences (ORFs 2+3), and the second recombinant contained ORF 3 alone. Expression from the construct containing both ORF 2 and ORF 3 resulted in the expression of a single protein (23K protein) detected by Western blot analysis with ORF 3-specific peptide antisera. However, expression from a construct containing only the ORF 3 coding sequences resulted in the production of multiple forms of the ORF 3 protein ranging in size from 23,000 to 35,000. Indirect-immunofluorescence studies using an ORF 3 peptide antiserum showed that the ORF 3 protein is localized to the cytoplasm of infected insect cells. The 23K ORF 3 protein was consistently associated with recombinant VLPs purified from the media of insect cells infected with a baculovirus recombinant containing the entire 3' end of the NV genome. Western blot analysis of NV purified from the stools of NV-infected volunteers revealed the presence of a 35K protein as well as multiple higher-molecular-weight bands specifically recognized by an ORF 3 peptide antiserum. These results indicate that the ORF 3 protein is a minor structural protein of the virion.

Norwalk virus vaccines: challenges and progress

Human caliciviruses (HuCVs) are the major cause of outbreaks of acute nonbacterial gastroenteritis throughout the world. An increasing recognition of the clinical significance of these viruses as human pathogens causing foodborne and waterborne disease indicates that an effective vaccine would be useful. This article reviews the current challenges that exist for the development of a vaccine for the HuCVs as well as the status of development of a candidate vaccine. HuCVs are viruses that exhibit a restricted tropism for infection of the gastrointestinal tract of humans, and a volunteer model of infection and disease is available. As pathogens with a restricted host range, the HuCVs are excellent models for understanding the mechanisms that mediate and regulate viral infection of the gastrointestinal tract and mucosal immunity in humans.

Dissolution of organic solvents from painted surfaces into water

The presence of volatile iodine in containment buildings is one of the major safety concerns in the potential event of nuclear reactor accidents. Organic impurities in containment water, originating from various painted structural surfaces and organic materials, could have a significant impact on iodine volatility following an accident. To determine the source and magnitude of organic impurities and their effects on time-dependent iodine volatility, the dissolution for organic constituents from paints used in reactor buildings has been studied under postulated accident conditions. The studies of the organic dissolution from carbon steel coupons coated with zinc-primed vinyl, epoxy-primed polyurethane or epoxy paints over the temperature range 25-90°C are reported. Relatively large activation energies were measured for the release of the principal organic compounds from painted surfaces, suggesting it is the release of the solvents from the paint matrix rather than their diffusion through the solution that is the rate determining step for the dissolution mechanism. The similarities in the values of activation energies for the dissolution of different organic compounds from the paints suggest the release rate is independent of the nature of the painted surface or the type of organic being released from the surface. These two observations indicate that it may be possible to write a generalized rate expression for the release of organic compounds from painted surfaces in containment following an accident. The possible implications of these results for predicting iodine volatility in containment are also discussed.Key words: dissolution kinetics, organic solvents, painted surfaces, reactor accidents.

Interaction of the N-terminus of sterol carrier protein 2 with membranes: role of membrane curvature

Although neither the physiological function nor the mechanism of action of sterol carrier protein 2 (SCP(2)) is yet completely clear, it is thought that SCP(2) interacts with membranes to elicit its biological effects. The results presented here show that the SCP(2) N-terminus, composed of two amphipathic alpha-helices, interacted preferentially with highly curved but not lower-curvature membranes containing anionic phospholipid. CD spectra of SCP(2) showed up to 1. 2-fold increased alpha-helical content, on the interaction of SCP(2) with small unilamellar vesicles (SUV) (median radius 10-14 nm) but less with large unilamellar vesicles (LUV) (median radius 52-60 nm). Although enhanced interaction with the SUV membranes was due in part to the radius of curvature and to the greater exposure of acidic phospholipid in the outer leaflet of the bilayer, simply increasing the molar percentage of acidic phospholipid in the LUV membranes had much less effect on SCP(2) binding. A similar preferential interaction was observed with highly curved SUV as opposed to LUV for the SCP(2) N-terminal peptide (1-32)SCP(2) as well as structurally modified peptides in the order (1-32)SCP(2)=(10-32)SCP(2)>(1-24)SCP(2)>>(1-E20-32)SCP(2). The CD results were confirmed with an independent filtration binding assay, which showed that SCP(2) bound 5-fold more to SUV than LUV, whereas its N-terminal peptides bound up to 4-fold better in the order (1-32)SCP(2)=(10-32)SCP(2)>(1-24)SCP(2)>(1-E20-32)SCP(2). Finally, cholesterol potentiated the binding of SCP(2) and N-terminal peptides to anionic-phospholipid-containing SUV but not LUV. These findings were consistent with the SCP(2) N-terminus being a membrane-binding domain that was highly dependent on membrane surface curvature as well as on lipid composition.

The sterol carrier protein-2 amino terminus: a membrane interaction domain

Sterol carrier protein-2 (SCP2) is a small, 123 amino acid, protein postulated to play a role in intracellular transport and metabolism of lipids such as cholesterol, phospholipids, and branched chain fatty acids. While it is thought that interaction of SCP2 with membranes is necessary for lipid transfer, evidence for this possibility and identification of a membrane interaction domain within SCP2 has remained elusive. As shown herein with circular dichroism and a direct binding assay, SCP2 bound to small unilamellar vesicle (SUV) membranes to undergo significant alteration in secondary structure. The SCP2 amphipathic N-terminal 32 amino acids, comprised of two alpha-helical segments, were postulated to represent a putative phospholipid interaction site. This hypothesis was tested with a series of SCP2 N-terminal peptides, circular dichroism, and direct binding studies. The SCP2 N-terminal peptide (1-32)SCP2, primarily random coil in aqueous buffer, adopted alpha-helical structure upon interaction with membranes. The induction of alpha-helical structure in the peptide was maximal when the membranes contained a high mole percent of negatively charged phospholipid and of cholesterol. While deletion of the second alpha-helical segment within this peptide had no effect on formation of the first alpha-helix, it significantly weakened the peptide interaction with membranes. Substitution of Leu(20) with Glu(20) in the N-terminal peptide disrupted the alpha-helix structure and greatly weakened the peptide interaction with membranes. Finally, deletion of the first nine nonhelical amino acids had no effect either on formation of alpha-helix or on peptide binding to membranes. N-Terminal peptide (1-32)SCP2 competed with SCP2 for binding to SUV. These data were consistent with the N-terminus of SCP2 providing a membrane interaction domain that preferentially bound to membranes rich in anionic phospholipid and cholesterol.

NSP4 elicits age-dependent diarrhea and Ca(2+)mediated I(-) influx into intestinal crypts of CF mice

Homologous disruption of the murine gene encoding the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) leads to the loss of cAMP-mediated ion transport. Mice carrying this gene defect exhibit meconium ileus at birth and gastrointestinal plugging during the neonatal period, both contributing to high rates of mortality. We investigated whether infectious mammalian rotavirus, the recently characterized rotaviral enterotoxin protein NSP4, or its active NSP4(114-135) peptide, can overcome these gastrointestinal complications in CF (CFTR(m3Bay) null mutation) mice. All three agents elicited diarrhea when administered to wild-type (CFTR(+/+)), heterozygous (CFTR(+/-)), or homozygous (CFTR(-/-)) 7- to 14-day-old mouse pups but were ineffective when given to older mice. The diarrheal response was accompanied by non-age-dependent intracellular Ca(2+) mobilization within both small and large intestinal crypt epithelia. Significantly, NSP4 elicited cellular I(-) influx into intestinal epithelial cells from all three genotypes, whereas both carbachol and the cAMP-mobilizing agonist forskolin failed to evoke influx in the CFTR(-/-) background. This unique plasma membrane halide permeability pathway was age dependent, being observed only in mouse pup crypts, and was abolished by either the removal of bath Ca(2+) or the transport inhibitor DIDS. These findings indicate that NSP4 or its active peptide may induce diarrhea in neonatal mice through the activation of an age- and Ca(2+)-dependent plasma membrane anion permeability distinct from CFTR. Furthermore, these results highlight the potential for developing synthetic analogs of NSP4(114-135) to counteract chronic constipation/obstructive bowel syndrome in CF patients.

Recombinant Norwalk virus-like particles given orally to volunteers: phase I study

BACKGROUND & AIMS

Norwalk virus (NV) is a major cause of epidemic gastroenteritis. The NV capsid is composed of a single protein that forms recombinant (rNV) virus-like particles (VLPs). In mice, these VLPs are immunogenic when administered orally without adjuvant, and they elicit serum immunoglobulin (Ig) G and intestinal IgA responses. The aim of this study was to evaluate the safety and immunogenicity of rNV VLPs in healthy volunteers.

METHODS

Twenty antibody-positive adults were orally administered rNV VLPs in sterile Milli-Q water on days 1 and 21. Vaccine safety and serum rNV-specific total and subclass IgG and IgA antibody responses were monitored. The immune response induced by the VLPs was compared with the response elicited by replicating virus.

RESULTS

No side effects were observed or reported by the volunteers. Serum IgG responses to rNV VLPs were dose-dependent, and all vaccinees given 250 microgram of rNV VLPs responded with >/=4-fold increases in serum IgG titers. Most of the volunteers (83%; 15 of 18) responded after the first rNV VLP dose and showed no increase in serum IgG titer after the second dose.

CONCLUSIONS

Orally administered rNV VLPs are safe and immunogenic in healthy adults when administered without adjuvant and are useful to test the mucosal delivery of immunogens.

Mutations in rotavirus nonstructural glycoprotein NSP4 are associated with altered virus virulence

Rotaviruses are major pathogens causing life-threatening dehydrating gastroenteritis in children and animals. One of the nonstructural proteins, NSP4 (encoded by gene 10), is a transmembrane, endoplasmic reticulum-specific glycoprotein. Recently, our laboratory has shown that NSP4 causes diarrhea in 6- to 10-day-old mice by functioning as an enterotoxin. To confirm the role of NSP4 in rotavirus pathogenesis, we sequenced gene 10 from two pairs of virulent and attenuated porcine rotaviruses, the OSU and Gottfried strains. Comparisons of the NSP4 sequences from these two pairs of rotaviruses suggested that structural changes between amino acids (aa) 131 and 140 are important in pathogenesis. We next expressed the cloned gene 10 from the OSU virulent (OSU-v) and OSU attenuated (OSU-a) viruses by using the baculovirus expression system and compared the biological activities of the purified proteins. NSP4 from OSU-v virus increased intracellular calcium levels over 10-fold in intestinal cells when added exogenously and 6-fold in insect cells when expressed endogenously, whereas NSP4 from OSU-a virus had little effect. NSP4 from OSU-v caused diarrhea in 13 of 23 neonatal mice, while NSP4 from OSU-a caused disease in only 4 of 25 mice (P < 0.01). These results suggest that avirulence is associated with mutations in NSP4. Results from site-directed mutational analyses showed that mutated OSU-v NSP4 with deletion or substitutions in the region of aa 131 to 140 lost its ability to increase intracellular calcium levels and to induce diarrhea in neonatal mice, confirming the importance of amino acid changes from OSU-v NSP4 to OSU-a NSP4 in the alteration of virus virulence.

Oral immunization with recombinant Norwalk virus-like particles induces a systemic and mucosal immune response in mice

Recombinant Norwalk virus-like particles (rNV VLPs) produced in insect cells were evaluated as an oral immunogen in CD1 and BALB/c mice by monitoring rNV-specific serum total and subclass immunoglobulin G (IgG) and intestinal IgA responses. Dose and kinetics of response were evaluated in the presence and absence of the mucosal adjuvant cholera toxin (CT). rNV-specific serum IgG and intestinal IgA were detected in the absence of CT, and the number of responders was not significantly different from that of mice administered VLPs with CT at most doses. The use of CT was associated with induction of higher levels of IgG in serum; this effect was greater at higher doses of VLPs. IgG in serum was detected in the majority of animals by 9 days postimmunization (dpi), and intestinal IgA responses were detected by 24 dpi. In the absence of CT, IgG2b was the dominant IgG subclass response in both mouse strains. Thus, nonreplicating rNV VLPs are immunogenic when administered orally in the absence of any delivery system or mucosal adjuvant. These studies demonstrate that rNV VLPs are an excellent model to study the oral delivery of antigen, and they are a potential mucosal vaccine for NV infections.

Basolateral sorting of the HIV type 2 and SIV envelope glycoproteins in polarized epithelial cells: role of the cytoplasmic domain

In polarized epithelial cell lines, enveloped viruses are directionally released by asymmetric viral budding at specific plasma membrane domains. Previous studies have shown that HIV-1 budding and gp160 expression occur on basolateral membranes whereas the release of HIV-1 Gag particles, in the absence of the Env glycoproteins, is nonpolarized. We have examined the directional transport and surface expression of HIV-2 and SIV envelope glycoproteins using vaccinia virus recombinants in Vero C1008 polarized epithelial cells. Analogous to HIV-1 gp160, both HIV-2 and SIV surface glycoproteins were preferentially directed to basolateral membranes. Hence basolateral expression appears to be a common property of the glycoproteins of primate lentiviruses. To explore the role of the cytoplasmic domain in directing the HIV-2 and SIV Env glycoproteins to the basolateral surface, stop codons were introduced to mimic the natural cytoplasmic truncations observed following repeated passage of these viruses in culture. These truncated glycoproteins also were sorted to the basolateral domain, but at a lower efficiency than the full-length protein product. In contrast, when the entire cytoplasmic domain of the SIV Env glycoprotein was deleted, the tailless SIV mutant was preferentially expressed on the apical surface. These data indicate the presence of a basolateral sorting signal in the cytoplasmic domain of primate lentiviral glycoproteins.

The rotavirus enterotoxin NSP4 mobilizes intracellular calcium in human intestinal cells by stimulating phospholipase C-mediated inositol 1,4,5-trisphosphate production

Rotavirus infection is the leading cause of severe diarrhea in infants and young children worldwide. The rotavirus nonstructural protein NSP4 acts as a viral enterotoxin to induce diarrhea and causes Ca2+-dependent transepithelial Cl- secretion in young mice. The cellular basis of this phenomenon was investigated in an in vitro cell line model for the human intestine. Intracellular calcium concentration ([Ca2+]i) was monitored in fura-2-loaded HT-29 cells using microscope-based fluorescence imaging. NSP4 (1 nM to 5 microM) induced both Ca2+ release from intracellular stores and plasmalemma Ca2+ influx. During NSP4-induced [Ca2+]i mobilization, [Na+]i homeostasis was not disrupted, demonstrating that NSP4 selectively regulated extracellular Ca2+ entry into these cells. The ED50 of the NSP4 effect on peak [Ca2+]i mobilization was 4.6 +/- 0.8 nM. Pretreatment of cells with either 2.3 x 10(-3) units/ml trypsin or 4.4 x 10(-2) units/ml chymotrypsin for 1-10 min abolished the NSP4-induced [Ca2+]i mobilization. Superfusing cells with U-73122, an inhibitor of phospholipase C, ablated the NSP4 response. NSP4 induced a rapid onset and transient stimulation of inositol 1,4,5-trisphosphate (IP3) production in an IP3-specific radioreceptor assay. Taken together, these results suggest that NSP4 mobilizes [Ca2+]i in human intestinal cells through receptor-mediated phospholipase C activation and IP3 production.

Prevalence of antibodies to human caliciviruses (HuCVs) in Kuwait established by ELISA using baculovirus-expressed capsid antigens representing two genogroups of HuCVs

Baculovirus recombinant-expressed antigens of Norwalk viruses (rNV) and a Mexico strain (rMX) of the Snow Mountain serogroup of human caliciviruses (HuCVs) were used in enzyme immunoassays to study the antibody prevalence among the Kuwaiti population and foreign workers employed in Kuwait. The antibody titers in 16 different age groups which ranged from neonates to centenarians were investigated by testing eight different dilutions of each serum (1:200-1:25,600). The results indicate that NV infection is widespread in Kuwait and affects all age groups Ninety-eight percent of the 433 serum samples tested had antibodies to rNV. In the 50-79-year, old age group, the antibody levels to rNV were higher and significantly different from those in children 0-7 years old. In infants, the rNV antibodies did not diminish by 4 months of age and their titer steadily increased with age. When 414 of these sera samples were tested for antibodies to rMX, 96% positive serological responses were observed. Antibody titers to rMX were reduced in infants from 4 to 11 months; however, 95% of the samples were positive. These data indicate that children born in Kuwait are infected with Norwalk-like viruses at a very early age. Finally, antibodies to rNV and rMX were found in 98% of 151 and in 95% of 148 foreign workers, respectively.

Proposed experimental tests of a theory of fine microstructure and the two-well problem

Predictions are made based on an analysis of a new nonlinear theory of martensitic transformations introduced by the authors. The crystal is modelled as a nonlinear elastic material, with a free-energy function that is invariant with respect to both rigid-body rotations and the appropriate crystallographic symmetries. The predictions concern primarily the two-well problem , that of determining all possible energy-minimizing deformations that can be obtained with two coherent and macroscopically unstressed variants of martensite. The set of possible macroscopic deformations obtained is completely determined by the lattice parameters of the material. For certain boundary conditions the total free energy does not attain a minimum , and the finer and finer oscillations of minimizing sequences are interpreted as corresponding to microstructure. The predictions are am enable to experimental tests. The proposed tests involve the comparison of the theoretical predictions with the mechanical response of properly oriented plates subject to simple shear.

Virus-like particle vaccines for mucosal immunization

Viruses which infect the gastrointestinal tract are well suited for examining the immune response(s) to oral delivery of antigen and exploring the advantages and pitfalls of oral vaccines. We have used recombinant DNA techniques to produce nonreplicating self-assembled virus-like particles (VLPs) from two gastrointestinal viruses, rotavirus and Norwalk virus. Both of these viruses normally cause acute gastroenteritis in man or animals. The VLPs are morphologically and antigenically similar to the native virus and quite stable, features which are advantageous for their use as subunit vaccines. In addition, these VLPs could be useful as carriers of foreign epitopes from heterologous pathogens or of drugs which need to be delivered to the gastrointestinal track. This paper briefly reviews the properties of these VLPs made in insect cells and data showing their potential as subunit vaccines for parenteral or oral delivery.

The rotavirus nonstructural glycoprotein NSP4 possesses membrane destabilization activity

During a unique morphogenetic process, rotaviruses obtain a transient membrane envelope when newly synthesized subviral particles bud into the endoplasmic reticulum (ER). As rotavirus particles mature, they lose their transient membrane and a layer of the glycoprotein VP7 forms the virion outer capsid shell. The nonstructural glycoprotein NSP4 functions as an intracellular receptor in the ER membrane (K. S. Au, W. K. Chan, J. W. Burns, and M. K. Estes, J. Virol. 63:4553-4562, 1989), and it has been hypothesized that NSP4 is involved in the removal of the envelope during viral morphogenesis (M. K. Estes and J. Cohen, Microbiol. Rev. 53:410-449, 1989; B. L. Petrie, M. K. Estes, and D. Y. Graham, J. Virol. 46:270-274, 1983). The purpose of the present study was to determine if NSP4 has a direct membrane destabilization activity (MDA) by using liposome leakage assays and electron microscopic visualization of liposome, microsome, and viral envelope disruption. The fluorescent marker (calcein) incorporated into liposomes was released when the liposomes were incubated with purified NSP4. A region corresponding to amino acid residues 114 to 135 of NSP4 also released calcein from liposomes. NSP4(114-135) peptide-specific antibody completely blocked the MDA of the purified NSP4 protein. These results suggest that this region contains at least part of the functional domain of NSP4. Liposomes composed of phosphatidylcholine and microsomes (to simulate ER membranes) were broken when observed by electron microscopy after incubation with NSP4 or the NSP4(114-135) peptide. In contrast, the envelope of Sendai virus, which is derived from cytoplasmic membranes, and erythrocytes were not disrupted by NSP4 and the NSP4(114-135) peptide. These results provide direct evidence that NSP4 possesses MDA and suggest that it can cause ER membrane damage. Therefore, NSP4 might play an important role in the removal of the transient envelope from budding particles during viral morphogenesis. A model for the MDA of NSP4 in viral morphogenesis is proposed.

Attachment and entry of recombinant Norwalk virus capsids to cultured human and animal cell lines

Norwalk virus (NV) is the prototype strain of a group of noncultivable human caliciviruses responsible for epidemic outbreaks of acute gastroenteritis. While these viruses do not grow in tissue culture cells or animal models, expression of the capsid protein in insect cells results in the self-assembly of recombinant Norwalk virus-like particles (rNV VLPs) that are morphologically and antigenically similar to native NV. We have used these rNV VLPs to examine virus-cell interactions. Binding and internalization of VLPs to cultured human and animal cell lines were studied in an attempt to identify potentially susceptible cell lines for virus propagation in vitro and to determine if early events in the replication cycle were responsible for the narrow host range and restriction of virus growth in cell culture. Radiolabeled VLPs specifically bound to a saturable number of binding molecules on the cell surface of 13 cell lines from different origins, including human intestine (differentiated and undifferentiated Caco-2) and insect (Spodoptera frugiperda 9) ovary. Differentiated Caco-2 cells bound significantly more rNV VLPs than the other cell lines. Variations in the amount of bound VLPs among the different cell lines did not correlate with the tissue or species of origin. VLP binding was specific, as determined by competition experiments with unlabeled rNV VLPs; however, only 1.4 to 6.8% of the specifically prebound radiolabeled VLPs became internalized into cells. Blocking experiments using polygonal and monoclonal anti-rNV sera and specific antipeptide sera were performed to map the domains on rNV VLPs involved in binding to cells. One monoclonal antibody (NV8812) blocked binding of rNV VLPs to human and animal cell lines. The binding site of monoclonal antibody NV8812 was localized to the C-terminal 300 to 384 residues of the capsid protein by immunoprecipitation with truncated and cleaved forms of the capsid protein. These data suggest that the C-terminal region of the capsid protein is involved in specific binding of rNV VLPs to cells.

Expression of Norwalk virus capsid protein in transgenic tobacco and potato and its oral immunogenicity in mice

Alternatives to cell culture systems for production of recombinant proteins could make very safe vaccines at a lower cost. We have used genetically engineered plants for expression of candidate vaccine antigens with the goal of using the edible plant organs for economical delivery of oral vaccines. Transgenic tobacco and potato plants were created that express the capsid protein of Norwalk virus, a calicivirus that causes epidemic acute gastroenteritis in humans. The capsid protein could be extracted from tobacco leaves in the form of 38-nm Norwalk virus-like particles. Recombinant Norwalk virus-like particle (rNV) was previously recovered when the same gene was expressed in recombinant baculovirus-infected insect cells. The capsid protein expressed in tobacco leaves and potato tubers cosedimented in sucrose gradients with insect cell-derived rNV and appeared identical to insect cell-derived rNV on immunoblots of SDS/polyacrylamide gels. The plant-expressed rNV was orally immunogenic in mice. Extracts of tobacco leaf expressing rNV were given to CD1 mice by gavage, and the treated mice developed both serum IgG and secretory IgA specific for rNV. Furthermore, when potato tubers expressing rNV were fed directly to mice, they developed serum IgG specific for rNV. These results indicate the potential usefulness of plants for production and delivery of edible vaccines. This is an appropriate technology for developing countries where vaccines are urgently needed.

Age-dependent diarrhea induced by a rotaviral nonstructural glycoprotein

The rotavirus nonstructural glycoprotein NSP4 is an intracellular receptor that mediates the acquisition of a transient membrane envelope as subviral particles bud into the endoplasmic reticulum. NSP4 also causes an increase in intracellular calcium in insect cells. Purified NSP4 or a peptide corresponding to NSP4 residues 114 to 135 induced diarrhea in young (6 to 10 days old) CD1 mice. This disease response was age-dependent, dose-dependent, and specific. Electrophysiologic data from intestinal mucosa showed that the NSP4 114-135 peptide potentiates chloride secretion by a calcium-dependent signaling pathway. Diarrhea is induced when NSP4, acting as a viral enterotoxin, triggers a signal transduction pathway.

Antigenic mapping of the recombinant Norwalk virus capsid protein using monoclonal antibodies

Norwalk virus (NV) is the prototype strain of a group of noncultivatable caliciviruses that infect humans and cause outbreaks of epidemic acute nonbacterial gastroenteritis. The NV virion is composed of 180 copies of a single structural protein that, when expressed in insect cells infected with a recombinant baculovirus, assembles into empty recombinant Norwalk virus-like particles (rNV VLPs) which are morphologically and antigenically similar to native NV. We have begun to dissect the antigenic structure of the rNV particles using monoclonal antibodies made to the rNV VLPs. Ten MAbs made to rNV particles were characterized for their reactivity as detector antibodies by ELISA, as capture antibodies in an ELISA to detect NV in stools, by Western blot, and by immunoprecipitation. Seven of the MAbs recognize discontinuous epitopes, requiring the rNV capsid protein to remain at least partially folded, while the other three recognize continuous epitopes. Eight of the MAbs map to the C-terminal half of the capsid protein as they react by Western blot and by immunoprecipitation with a 32K trypsin cleavage product of the full-length 58K capsid protein, suggesting that the C-terminal half of the capsid protein may contain the immunodominant epitopes. The three MAbs that recognize continuous epitopes map to the extreme C terminus of the capsid protein, between amino acids 457 and 530, in a region that is relatively conserved among different human calicivirus capsid proteins. These MAbs which were assigned into three antigenic groups will be useful as tools to further dissect the structural and antigenic topography of the NV virion, and as unlimited reagents to detect NV in diagnostic assays.

Rotavirus protein expression is important for virus assembly and pathogenesis

Rotaviruses have a unique morphogenesis in which particles obtain a transient membrane-envelope as newly made subviral particles bud into the endoplasmic reticulum (ER). This process is mediated by a viral nonstructural glycoprotein, NSP4. We have found that NSP4 has pleiotropic properties that became evident following expression of this protein in eukaryotic cells. NSP4 expressed in insect cells bound double-layered rotavirus particles in a manner similar to receptor-ligand interactions and this interaction is thought to trigger the particle budding process. Expression of NSP4 in insect cells also increases intracellular calcium ([Ca2+]i) levels and this effect may explain the toxicity of this protein in eukaryotic cells. Increases in [Ca2+]i levels in insect cells also are observed following exogenous addition to cells of purified NSP4 or of a synthetic peptide of NSP4. Experiments to determine the mechanism by which NSP4 causes an increase in [Ca2+]i showed that Ca2+ is released from a subset of the thapsigargin-sensitive store [endoplasmic reticulum (ER)]. However, exogenously added and endogenously expressed NSP4 use different mechanisms to alter the Ca2+ permeability of the ER membrane. We hypothesize that NSP4-mediated changes in ER membrane permeability trigger viral budding into the lumen of the ER, and eventually induce cell death and release of virus particles from infected cells. We also propose that release of NSP4 following cell lysis and the concomitant stimulation of a Ca2+ signal transduction pathway in neighboring cells contributes to altered ion transport in intestinal epithelium resulting in diarrheal disease.

Recombinant Norwalk virus-like particles as an oral vaccine

Viruses that infect cells in the gastrointestinal tract are well suited for examining the immune response to oral delivery of antigen and for exploring the advantages and pitfalls of oral vaccines. Norwalk virus (NV) (family Caliciviridae, genus Calicivirus) causes acute gastroenteritis in all age groups. The NV capsid is composed of 180 copies of a single 58000 molecular weight protein which spontaneously forms virus-like particles (VLPs) that can be purified in extremely high yields (22 mg per 300 ml culture) when produced using the baculovirus expression system. We are testing the potential of these recombinant NV (rNV) particles for use as an oral vaccine by administering them to mice and volunteers. Mice were orally inoculated four times with rNV particles in concentrations ranging from 5 to 500 micrograms in the absence of adjuvant or from 5 to 200 micrograms with 10 micrograms of cholera toxin. Serum IgG and fecal IgA immune responses were monitored. rNV particles were found to be immunogenic when orally given to mice with or without adjuvant. These particles also were safe and immunogenic when orally given to volunteers. These studies show that rNV particles are an excellent model to test the oral delivery of mucosal immunogens in general, and that rNV particles are ideal candidates for vaccine development in particular.

Antibody prevalence and immunoglobulin IgG subclass pattern to Norwalk virus in Sweden

The antibody prevalence in Sweden to Norwalk virus (NV) was investigated using a baculovirus expressed capsid antigen. One hundred thirty-two serum samples were examined for IgA, total IgG and IgG subclass antibodies to Norwalk virus. In young children, NV IgG antibody prevalence was higher than the IgA prevalence, whereas no difference was found in individuals older than 21 years. The IgG antibody prevalence was 50% in children below 5 years of age and increased to > 80% in individuals older than 10 years of age. To examine the IgG antibody response in more detail, IgG subclass patterns were characterized. IgG 1 predominated in all age groups. IgG 4, usually detected after repeated exposure to antigen, was the second most prevalent subclass, but was only found in individuals older than 21 years of age. IgG 3 subclass antibodies were found in 13% and IgG 2 in 3% of the sera examined. IgG 3 subclass antibodies have been recognized as a marker for recent or ongoing viral infections.

Monoclonal antibodies for detection of Norwalk virus antigen in stools

Monoclonal antibodies against the prototype 8FIIa strain of Norwalk virus were prepared and applied to an enzyme immunoassay (EIA) for detecting Norwalk virus in stool specimens. The monoclonal antibodies immunoprecipitated a 58-kDa protein which had been produced by in vitro transcription-translation of Norwalk virus cloned cDNA, and they reacted by EIA with recombinant Norwalk virus capsid protein at a sensitivity level of 1 ng/ml. The EIA detected virus in all tested samples from 15 different Norwalk virus-infected volunteers. No cross-reactions were seen in stools containing other caliciviruses or in stools containing rotaviruses, astroviruses, or enteric adenoviruses.

The rotavirus nonstructural glycoprotein NSP4 mobilizes Ca2+ from the endoplasmic reticulum

We previously reported that expression of rotavirus nonstructural glycoprotein NSP4 is responsible for an increase in cytosolic free Ca2+ concentration ([Ca2+]i) in Spodoptera frugiperda (Sf9) insect cells (P. Tian, Y. Hu, W. P. Schilling, D. A. Lindsay, J. Eiden, and M. K. Estes, J. Virol. 68:251-257, 1994). The purpose of the present study was to determine the mechanism by which NSP4 causes an increase in [Ca2+]i by measuring the permeability of the cytoplasmic and endoplasmic reticulum (ER) membranes in recombinant-baculovirus-infected Sf9 cells. No obvious change in plasmalemma permeability to divalent cations was observed in cells expressing NSP4 compared with that in cells expressing another rotaviral glycoprotein (VP7) when the influx of Ba2+, a Ca2+ surrogate, was monitored. The basal Ca2+ permeability of the internal Ca2+ store was evaluated by measuring the release of Ca2+ induced by ionomycin, a Ca2+ ionophore, or thapsigargin, an inhibitor of the ER Ca(2+)-ATPase pump, following suspension of the cells in Ca(2+)-free extracellular buffer. Releasable Ca2+ decreased with time to a greater extent in cells expressing NSP4 compared with that in cells expressing VP7, suggesting that NSP4 increases the basal Ca2+ permeability of the ER membrane. To determine the possible mechanism by which NSP4 increases ER permeability, purified NSP4 protein or a 22-amino-acid synthetic peptide consisting of residues 114 to 135 (NSP4(114-135) was added exogenously to noninfected Sf9 cells during measurement of [Ca2+]i. Both NSP4 and the NSP4(114-135 peptide produced a time-dependent increase in [Ca2+]i that was attenuated by prior inhibition of phospholipase C with U-73122. Pretreatment of the cells with thapsigargin completely blocked the increase in [Ca2+]i produced by NSP4(114-135, but the peptide only partially reduced the change in [Ca2+]i produced by thapsigargin. No changes in [Ca2+]i were seen in cells treated with control peptides. These results suggest that (i) exogenous NSP4 increases [Ca2+]i through the activation of phospholipase C, (ii) Ca2+ release by exogenous NSP4 is from a store that is a subset of the thapsigargin-sensitive compartment, and (iii) amino acid residues 114 to 135 of NSP4 are sufficient for this activity. In contrast to exogenous NSP4, the mechanism by which endogenously expressed NSP4 increases [Ca2+]1 appears to be unrelated to phospholipase C, since no effect of U-73122 was seen on the elevated [Ca2+]1 in cells expressing NSP4 and exogenously applied NSP4(114-135) caused a further increase in [Ca2+]1 in cells expressing NSP4 protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Specific proteolytic cleavage of recombinant Norwalk virus capsid protein

Norwalk virus (NV) causes epidemic outbreaks of acute nonbacterial gastroenteritis in humans. The NV capsid is made up of a single protein, and expression of the capsid protein in baculovirus recombinants results in spontaneous assembly of the protein into virus-like particles (X. Jiang, M. Wang, D. Y. Graham, and M. K. Estes, J. Virol. 66:6527-6532, 1992). We have investigated whether the NV capsid protein undergoes a specific proteolytic cleavage. Recombinant NV (rNV) particles were digested with trypsin to determine if a specific cleavage occurred. A predominant band with a molecular weight of approximately 32,000 (32K protein) was observed when trypsin-treated rNV was electrophoresed on sodium dodecyl sulfate-polyacrylamide gels. Determination of the N-terminal sequence of this band showed that a trypsin-specific cleavage occurred at amino acid residue 227. Early studies identified two proteins with molecular weights of 59,000 and 30,000 (59K and 30K proteins) in the stool of NV-infected volunteers that were reactive with postinfection antiserum. (H. B. Greenberg, J. R. Valdesuso, A. R. Kalica, R. G. Wyatt, V. J. McAuliffe, A. Z. Kapikian, and R. M. Chanock, J. Virol. 37:994-999, 1981). We hypothesized that the 32K rNV cleavage product might be analogous to the 30K soluble protein detected in stools of NV-infected volunteers. Immunoprecipitation of soluble protein from these stool extracts with a rabbit polyclonal antiserum made against rNV, and Western blot detection with a mouse polyclonal antiserum made against rNV, revealed a single band with an apparent molecular weight of 30,000 that migrated similarly to the trypsin cleavage product observed in vitro. The N terminus of this band was identical to that of the 32K cleavage product of rNV capsid protein. These data show that the 30K protein in stool is produced by specific cleavage of the NV capsid protein in vivo. Trypsin cleavage of isolated soluble rNV 58K capsid protein and of assembled particles showed that only soluble 58K capsid protein is susceptible to cleavage. The presence of a large amount of soluble capsid protein may influence the immune response to or pathogenicity of NV infections.

A polarized human endometrial cell line that binds and transports polymeric IgA

We have demonstrated that a human endometrial cell line, HEC-1, maintains a transepithelial electrical resistance, directionally transports fluids across the cell monolayer, and releases enveloped viruses at distinct plasma membrane domains: influenza virus is released at the apical surfaces and vesicular stomatitis virus (VSV) at the basolateral surfaces. In addition, we have examined the expression of domain-specific endogenous proteins, including the polyimmunoglobulin receptor. Multiple endogenous polypeptides were found to be secreted into the culture medium at basolateral surfaces, whereas no secretion of specific polypeptides was observed from apical cell surfaces. Distinct patterns of endogenous proteins were also observed on apical and basolateral cell surfaces, with a much more complex polypeptide pattern on the basolateral membranes. Using surface biotinylation and immunofluorescence, the polyimmunoglobulin receptor was found to be expressed on the basolateral surface of HEC-1 monolayers. The specific binding of poly-immunoglobulin A (pIgA) was found to occur on the basolateral surface, and was followed by transcytosis to the apical surface and release into the apical medium. The observed characteristics indicate that the endometrium-derived HEC-1 epithelial cell line can be employed as a model for studies of protein transport in polarized epithelial cells of human endometrial tissues, as well as for studies of the interaction of microorganisms with epithelial cells in the genital tract.

A general model for the surface glycoproteins of HIV and other retroviruses

A hypothetical model of the surface (SU) glycoproteins of human immunodeficiency virus (HIV) and other retroviruses is proposed. The model is based on repetition of a limited number of sequence motifs conserved within the virus family; similarities in biological, immunological, or genetic properties; as well as the tendency for regions of dissimilar sequence to share protein structures predicted by computer algorithms. It is proposed that the protein consists of three structural and functional domains interspersed by relatively conserved interdomain regions. For each retrovirus, these amino-terminal, central, and carboxy-terminal domains may play different roles in binding, postbinding events, and the immune response to viral infection.

A versatile synthetic peptide-based ELISA for identifying antibody epitopes

A simple, versatile and very inexpensive procedure for cross-linking synthetic peptides to the polystyrene surfaces of micro-well assay plates for use in ELISA was developed. The method is based on the use of poly-L-lysine (PLL) as the anchor protein for synthetic peptides which were then easily and covalently linked to the PLL using glutaraldehyde. The synthetic peptides used for the study were based on the amino acid sequence of the equine infectious anemia virus (EIAV) envelope sequence and evaluated as antigens in an ELISA designed to detect antibodies in serum of EIAV-infected horses and ponies. The ELISA using cross-linked peptides proved to be significantly more sensitive when compared to assays where passively coated peptides were used. In one instance, a peptide was identified that was not recognized by any of our antisera and appeared not to bind to the assay plates. However, once this peptide was cross-linked to the assay plate it proved to be very useful for detecting EIAV-specific antibodies. This cross-linking approach functioned equally well with peptides of various charges and sizes and did not appear to alter epitopes contained in the peptides.

Detailed mapping of the antigenicity of the surface unit glycoprotein of equine infectious anemia virus by using synthetic peptide strategies

We describe here a detailed analysis of the antigenic determinants of the surface unit glycoprotein (gp90) of equine infectious anemia virus (EIAV), using a comprehensive panel of synthetic peptides in enzyme-linked immunosorbent assays with immune serum from naturally and experimentally infected horses and with a panel of gp90-specific neutralizing and nonneutralizing monoclonal antibodies. The results of these studies identify immunoreactive segments throughout the conserved and variable domains of gp90 but localize immunodominant (100% reactivity) determinants to the amino and carboxyl termini of the glycoprotein molecule. Analysis of peptide reactivities with longitudinal serum samples taken from experimentally infected ponies revealed that antibody responses to conserved B-cell determinants appeared earlier and at higher titers than do antibodies specific for determinants contained in the variable domain of gp90. These observations suggest an evolution of antibody responses in EIAV-infected ponies that may correspond to the establishment of immunological control of virus replication and disease routinely observed in EIAV infections. In addition, the mapping of monoclonal antibody epitopes to peptides of 9 to 12 amino acids demonstrated that all of the neutralizing epitopes are located in the variable domain of gp90. The arrangement of neutralizing epitopes and critical structural considerations suggest that EIAV gp90 contains a principal neutralizing domain similar to the V3 loop of human immunodeficiency virus type 1. These antigenic analyses provide an important foundation for further analyzing the protective immune response generated during persistent EIAV infections and also provide potential peptide substrates for diagnostic assays and for vaccine strategies.

Hypothalamic regulatory peptides in obese and lean Zucker rats

1. Hypothalamic concentrations of nine peptides with experimental effects on energy balance were compared in obese (fa/fa) and lean (Fa/?) male Zucker rats. To determine whether any peptide differences between obese and lean rats might be due to the overweight condition per se, separate groups of obese rats were food-restricted to reduce their body weight to lean values. 2. Concentrations of neuromedin B, a bombesin-like peptide, in the central hypothalamus were significantly higher in obese than in lean rats. This difference was not affected in food-restricted obese rats. 3. Hypothalamic levels of neuropeptide Y, an extremely potent central appetite stimulant, were similar in lean and freely fed obese rats but central hypothalamic levels of neuropeptide Y rose significantly in food-restricted obese rats. 4. These findings suggest that disturbances in hypothalamic neuromedin B concentrations may be involved in the obesity syndrome of the fa/fa Zucker rat. Increased central hypothalamic levels of neuropeptide Y in food-restricted rats suggest that this peptide may help to defend body weight by stimulating eating after weight loss.

Analysis of equine humoral immune responses to the transmembrane envelope glycoprotein (gp45) of equine infectious anemia virus

Defined segments of the transmembrane envelope glycoprotein (gp45) of equine infectious anemia virus were expressed as TrpLE fusion proteins and examined for their reactivity in Western immunoblots against a diverse panel of equine immune sera. The most immunogenic region of gp45 was localized to its amino terminus, positioned between the hydrophobic fusion and the transmembrane domains. A series of overlapping synthetic peptides were used in enzyme-linked immunosorbent assays to define an immunodominant epitope within this region. In contrast, the carboxy-terminal half of gp45 displayed both weak and variable immunoreactivity with equine immune sera.

A survey of potential problems and quality control in peptide synthesis by the fluorenylmethoxycarbonyl procedure

The routine production of peptides by manual or automated solid-phase synthesis protocols has gained widespread usage among a variety of biological scientists as new synthetic procedures have been introduced over the past several years. We report here a detailed analysis of Fmoc synthesis procedures to identify problematic reactions and to evaluate analytical procedures for monitoring the quality of peptides during and after synthesis. The results of these studies demonstrate double additions of particular amino acids during single coupling cycles, frequent incomplete deblocking of peptides by standard piperidine reactions, and the failure of the Kaiser ninhydrin test to detect free amino groups of certain amino acids at the N-terminus of synthetic peptides. These results suggest the need for more careful monitoring of Fmoc synthesis reactions than previously recognized or recommended in standard protocols. We demonstrate the utility of plasma desorption mass spectrometry (PDMS) in analyzing peptide products and recommend a minimum sequence of analytical quality control including HPLC and PDMS.

A general model for the transmembrane proteins of HIV and other retroviruses

A hypothetical model of the transmembrane (TM) protein of human immunodeficiency virus (HIV) is proposed that is derived from the known structure of the influenza TM protein HA2. This model is consistent with computer algorithms of predicted protein structure and with known properties of TM proteins determined by sequence homology, site-directed mutations, peptide analogs, immunochemistry, or other biologic means. It is applicable to a wide variety of retroviral TM proteins differing widely in overall molecular weight.