Recombinant rhodostomin substrates induce transformation and active calcium oscillation in human platelets

Exposure of Platelets to Dengue Virus and Envelope Protein Domain III Induces Nlrp3 Inflammasome-Dependent Platelet Cell Death and Thrombocytopenia in Mice

In tropical and subtropical regions, mosquito-borne dengue virus (DENV) infections can lead to severe dengue, also known as dengue hemorrhage fever, which causes bleeding, thrombocytopenia, and blood plasma leakage and increases mortality. Although DENV-induced platelet cell death was linked to disease severity, the role of responsible viral factors and the elicitation mechanism of abnormal platelet activation and cell death remain unclear. DENV and virion-surface envelope protein domain III (EIII), a cellular binding moiety of the virus particle, highly increase during the viremia stage. Our previous report suggested that exposure to such viremia EIII levels can lead to cell death of endothelial cells, neutrophils, and megakaryocytes. Here we found that both DENV and EIII could induce abnormal platelet activation and predominantly necrotic cell death pyroptosis. Blockages of EIII-induced platelet signaling using the competitive inhibitor chondroitin sulfate B or selective Nlrp3 inflammasome inhibitors OLT1177 and Z-WHED-FMK markedly ameliorated DENV- and EIII-induced thrombocytopenia, platelet activation, and cell death. These results suggest that EIII could be considered as a virulence factor of DENV, and that Nlrp3 inflammasome is a feasible target for developing therapeutic approaches against dengue-induced platelet defects.

Thioacetamide-induced liver damage and thrombocytopenia is associated with induction of antiplatelet autoantibody in mice

Thrombocytopenia is usually associated with liver injury, elevated plasma aspartate aminotransferase and alanine aminotransferase levels, and high antiplatelet immunoglobulin (Ig) titers, although the mechanism behind these effects remains elusive. Deciphering the mechanism behind acute liver disease–associated thrombocytopenia may help solve difficulties in routine patient care, such as liver biopsy, antiviral therapy, and surgery. To determine whether liver damage is sufficient per se to elicit thrombocytopenia, thioacetamide (TAA)-induced hepatitis rodent models were employed. The analysis results indicated that TAA treatment transiently induced an elevation of antiplatelet antibody titer in both rats and mice. B-cell-deficient (BCD) mice, which have loss of antibody expression, exhibited markedly less thrombocytopenia and liver damage than wild-type controls. Because TAA still induces liver damage in BCD mice, this suggests that antiplatelet Ig is one of the pathogenic factors, which play exacerbating role in the acute phase of TAA-induced hepatitis. TNF-α was differentially regulated in wild-type versus BCD mice during TAA treatment, and anti-TNF treatment drastically ameliorated antiplatelet Ig induction, thrombocytopenia, and liver injury, suggesting that the TNF pathway plays a critical role in the disease progression.

Recombinant and Chimeric Disintegrins in Preclinical Research

Disintegrins are a family of small cysteine-rich peptides, found in a wide variety of snake venoms of different phylogenetic origin. These peptides selectively bind to integrins, which are heterodimeric adhesion receptors that play a fundamental role in the regulation of many physiological and pathological processes, such as hemostasis and tumor metastasis. Most disintegrins interact with integrins through the RGD (Arg-Gly-Asp) sequence loop, resulting in an active site that modulates the integrin activity. Some variations in the tripeptide sequence and the variability in its neighborhood result in a different specificity or affinity toward integrin receptors from platelets, tumor cells or neutrophils. Recombinant forms of these proteins are obtained mainly through Escherichia coli, which is the most common host used for heterologous expression. Advances in the study of the structure-activity relationship and importance of some regions of the molecule, especially the hairpin loop and the C-terminus, rely on approaches such as site-directed mutagenesis and the design and expression of chimeric peptides. This review provides highlights of the biological relevance and contribution of recombinant disintegrins to the understanding of their binding specificity, biological activities and therapeutic potential. The biological and pharmacological relevance on the newest discoveries about this family of integrin-binding proteins are discussed.

Soluble P-selectin rescues mice from anthrax lethal toxin-induced mortality through PSGL-1 pathway-mediated correction of hemostasis

As one of the virulence factors of Bacillus anthracis, lethal toxin (LT) induces various pathogenic responses including the suppression of the coagulation system. In this study, we observed that LT markedly increased the circulating soluble P-selectin (sP-sel) levels and microparticle (MP) count in wild-type but not P-selectin (P-sel, Selp^-/-) or P-sel ligand-1 (PSGL-1, Selplg^-/-) knockout mice. Because sP-sel induces a hypercoagulable state through PSGL-1 pathway to generate tissue factor-positive MPs, we hypothesized that the increase in plasma sP-sel levels can be a self-rescue response in hosts against the LT-mediated suppression of the coagulation system. In agreement with our hypothesis, our results indicated that compared with wild-type mice, Selp^-/- and Selplg^-/- mice were more sensitive to LT. In addition, the recombinant sP-sel treatment markedly ameliorated LT-mediated pathogenesis and reduced mortality. As a result, elicitation of circulating sP-sel is potentially a self-rescue response, which is beneficial to host recovery from an LT-induced hypocoagulation state. These results suggest that the administration of sP-sel is likely to be useful in the development of a new strategy to treat anthrax.

Visible Light-Responsive Platinum-Containing Titania Nanoparticle-Mediated Photocatalysis Induces Nucleotide Insertion, Deletion and Substitution Mutations

Conventional photocatalysts are primarily stimulated using ultraviolet (UV) light to elicit reactive oxygen species and have wide applications in environmental and energy fields, including self-cleaning surfaces and sterilization. Because UV illumination is hazardous to humans, visible light-responsive photocatalysts (VLRPs) were discovered and are now applied to increase photocatalysis. However, fundamental questions regarding the ability of VLRPs to trigger DNA mutations and the mutation types it elicits remain elusive. Here, through plasmid transformation and β-galactosidase α-complementation analyses, we observed that visible light-responsive platinum-containing titania (TiO₂) nanoparticle (NP)-mediated photocatalysis considerably reduces the number of Escherichia coli transformants. This suggests that such photocatalytic reactions cause DNA damage. DNA sequencing results demonstrated that the DNA damage comprises three mutation types, namely nucleotide insertion, deletion and substitution; this is the first study to report the types of mutations occurring after photocatalysis by TiO₂-VLRPs. Our results may facilitate the development and appropriate use of new-generation TiO₂ NPs for biomedical applications.

Soluble P-selectin rescues viper venom-induced mortality through anti-inflammatory properties and PSGL-1 pathway-mediated correction of hemostasis

Venomous snakebites are lethal and occur frequently worldwide each year, and receiving the antivenom antibody is currently the most effective treatment. However, the specific antivenom might be unavailable in remote areas. Snakebites by Viperidae usually lead to hemorrhage and mortality if untreated. In the present study, challenges of rattlesnake (Crotalus atrox) venom markedly increased the circulating soluble P-selectin (sP-sel) level, but not P-selectin (P-sel, Selp^−/−) mutants, in wild-type mice. Because sP-sel enhances coagulation through the P-selectin ligand 1 (PSGL-1, Selplg) pathway to produce tissue factor–positive microparticles, we hypothesized that increasing the plasma sP-sel level can be a self-rescue response in hosts against snake venom–mediated suppression of the coagulation system. Confirming our hypothesis, our results indicated that compared with wild-type mice, Selp^−/− and Selplg^−/− mice were more sensitive to rattlesnake venom. Additionally, administration of recombinant sP-sel could effectively reduce the mortality rate of mice challenged with venoms from three other Viperidae snakes. The antivenom property of sP-sel is associated with improved coagulation activity in vivo. Our data suggest that the elevation of endogenous sP-sel level is a self-protective response against venom-suppressed coagulation. The administration of recombinant sP-sel may be developed as a new strategy to treat Viperidae snakebites.

Cell adhesion as a novel approach to determining the cellular binding motif on the severe acute respiratory syndrome coronavirus spike protein

Emerging life threatening pathogens such as severe acute aspiratory syndrome-coronavirus (SARS-CoV), avian-origin influenzas H7N9, and the Middle East respiratory syndrome coronavirus (MERS-CoV) have caused a high case-fatality rate and psychological effects on society and the economy. Therefore, a simple, rapid, and safe method to investigate a therapeutic approach against these pathogens is required. In this study, a simple, quick, and safe cell adhesion inhibition assay was developed to determine the potential cellular binding site on the SARS-CoV spike protein. Various synthetic peptides covering the potential binding site helped to minimize further the binding motif to 10–25 residues. Following analyses, 2 peptides spanning the 436–445 and 437–461 amino acids of the spike protein were identified as peptide inhibitor or peptide vaccine candidates against SARS-CoV.

Applications of snake venom components to modulate integrin activities in cell-matrix interactions

Snake venom proteins are broadly investigated in the different areas of life science. Direct interaction of these compounds with cells may involve a variety of mechanisms that result in diverse cellular responses leading to the activation or blocking of physiological functions of the cell. In this review, the snake venom components interacting with integrins will be characterized in context of their effect on cellular response. Currently, two major families of snake venom proteins are considered as integrin-binding molecules. The most attention has been devoted to the disintegrin family, which binds certain types of integrins through specific motifs recognized as a tri-peptide structurally localized on an integrin-binding loop. Other snake venom integrin-binding proteins belong to the C-type lectin family. Snake venom molecules bind to the cellular integrins resulting in a modulation of cell signaling and in consequence, the regulation of cell proliferation, migration and apoptosis. Therefore, snake venom research on the integrin-binding molecules may have significance in biomedicine and basic cell biology.

Suppressive effects of anthrax lethal toxin on megakaryopoiesis

Anthrax lethal toxin (LT) is a major virulence factor of Bacillus anthracis. LT challenge suppresses platelet counts and platelet function in mice, however, the mechanism responsible for thrombocytopenia remains unclear. LT inhibits cellular mitogen-activated protein kinases (MAPKs), which are vital pathways responsible for cell survival, differentiation, and maturation. One of the MAPKs, the MEK1/2-extracellular signal-regulated kinase pathway, is particularly important in megakaryopoiesis. This study evaluates the hypothesis that LT may suppress the progenitor cells of platelets, thereby inducing thrombocytopenic responses. Using cord blood-derived CD34(+) cells and mouse bone marrow mononuclear cells to perform in vitro differentiation, this work shows that LT suppresses megakaryopoiesis by reducing the survival of megakaryocytes. Thrombopoietin treatments can reduce thrombocytopenia, megakaryocytic suppression, and the quick onset of lethality in LT-challenged mice. These results suggest that megakaryocytic suppression is one of the mechanisms by which LT induces thrombocytopenia. These findings may provide new insights for developing feasible approaches against anthrax.

Platelets in inflammation and immune modulations: functions beyond hemostasis

Platelets play central roles for maintaining the homeostasis of the blood coagulation. As they are also involved in immune responses and host defenses, increasing evidences have suggested that platelets exert other roles beyond their well-recognized function in preventing bleeding. This review is focused on inflammation, allergy and immune modulations of platelets. Platelets conduct immunoregulation through secretion of functional mediators, interaction with various immune cells, endothelial cells and beneficial for the leukocyte infiltration to inflamed/allergic tissues. In these regulations, the leukocytes are influenced by and receiving the signals from platelets. In contrast, rare attentions were focused on platelet regulations by immune system. An intriguingly example in the intravenous immunoglobulin (IVIg) treatment is discussed, in which dendritic cells exert anti-inflammatory effect through platelets. This further suggests that coagulant and immune systems are tightly associated rather than separate entities. The cross-talks between these two systems implicate that platelet therapy may have application beyond thrombosis, and immune interventions may have potentials to treat thrombosis diseases.

The use of nanoscale visible light-responsive photocatalyst TiO2-Pt for the elimination of soil-borne pathogens

Exposure to the soil-borne pathogens Burkholderia pseudomallei and Burkholderia cenocepacia can lead to severe infections and even mortality. These pathogens exhibit a high resistance to antibiotic treatments. In addition, no licensed vaccine is currently available. A nanoscale platinum-containing titania photocatalyst (TiO₂-Pt) has been shown to have a superior visible light-responsive photocatalytic ability to degrade chemical contaminants like nitrogen oxides. The antibacterial activity of the catalyst and its potential use in soil pathogen control were evaluated. Using the plating method, we found that TiO₂-Pt exerts superior antibacterial performance against Escherichia coli compared to other commercially available and laboratory prepared ultraviolet/visible light-responsive titania photocatalysts. TiO₂-Pt-mediated photocatalysis also affectively eliminates the soil-borne bacteria B. pseudomallei and B. cenocepacia. An air pouch infection mouse model further revealed that TiO₂-Pt-mediated photocatalysis could reduce the pathogenicity of both strains of bacteria. Unexpectedly, water containing up to 10% w/v dissolved soil particles did not reduce the antibacterial potency of TiO₂-Pt, suggesting that the TiO₂-Pt photocatalyst is suitable for use in soil-contaminated environments. The TiO₂-Pt photocatalyst exerted superior antibacterial activity against a broad spectrum of human pathogens, including B. pseudomallei and B. cenocepacia. Soil particles (<10% w/v) did not significantly reduce the antibacterial activity of TiO₂-Pt in water. These findings suggest that the TiO₂-Pt photocatalyst may have potential applications in the development of bactericides for soil-borne pathogens.

Integrin-mediated membrane blebbing is dependent on sodium-proton exchanger 1 and sodium-calcium exchanger 1 activity

Integrin signaling and membrane blebbing modulate cell adhesion, spreading, and migration. However, the relationship between integrin signaling and membrane blebbing is unclear. Here, we show that an integrin-ligand interaction induces both membrane blebbing and changes in membrane permeability. Sodium-proton exchanger 1 (NHE1) and sodium-calcium exchanger 1 (NCX1) are membrane proteins located on the bleb membrane. Inhibition of NHE1 disrupts membrane blebbing and decreases changes in membrane permeability. However, inhibition of NCX1 enhances cell blebbing; cells become swollen because of NHE1 induced intracellular sodium accumulation. Our study found that NHE1 induced sodium influx is a driving force for membrane bleb growth, while sodium efflux (and calcium influx) induced by NCX1 in a reverse mode results in membrane bleb retraction. Together, these findings reveal a novel function for NHE1 and NCX1 in membrane blebbing and permeability, and establish a link between membrane blebbing and integrin signaling.

The effects of the bacterial interaction with visible-light responsive titania photocatalyst on the bactericidal performance

Bactericidal activity of traditional titanium dioxide (TiO₂) photocatalyst is effective only upon irradiation by ultraviolet light, which restricts the potential applications of TiO₂ for use in our living environments. Recently carbon-containing TiO₂ was found to be photoactive at visible-light illumination that affords the potential to overcome this problem; although, the bactericidal activity of these photocatalysts is relatively lower than conventional disinfectants. Evidenced from scanning electron microscopy and confocal Raman spectral mapping analysis, we found the interaction with bacteria was significantly enhanced in these anatase/rutile mixed-phase carbon-containing TiO₂. Bacteria-killing experiments indicate that a significantly higher proportion of all tested pathogens including Staphylococcus aureus, Shigella flexneri and Acinetobacter baumannii, were eliminated by the new nanoparticle with higher bacterial interaction property. These findings suggest the created materials with high bacterial interaction ability might be a useful strategy to improve the antimicrobial activity of visible-light-activated TiO₂.

Stepped changes of monovalent ligand-binding force during ligand-induced clustering of integrin alphaIIB beta3

Recent evidence demonstrated that conformational changes of the integrin during receptor activation affected its binding to extracellular matrix; however, experimental assessment of ligand-receptor binding following the initial molecular interaction has rarely been carried out at a single-molecule resolution. In the present study, laser tweezers were used to measure the binding force exerted by a live Chinese hamster ovary cell that expressed integrin alphaIIb beta3 (CHO alphaIIb beta3), to the bead carrier coated with the snake venom rhodostomin that served as an activated ligand for integrin alphaIIb beta3. A progressive increase of total binding force over time was noticed when the bead interacted with the CHO alphaIIb beta3 cell; such an increase was due mainly to the recruitment of more integrin molecules to the bead-cell interface. When the binding strength exerted by a single ligand-receptor pair was derived from the "polyvalent" measurements, surprisingly, a stepped decrease of the "monovalent binding force" was noted (from 4.15 to 2.54 piconewtons (pN)); such decrease appeared to occur during the ligand-induced integrin clustering process. On the other hand, the mutant rhodostomin defective in clustering integrins exhibited only one (1.81 pN) unit binding strength.

The integrin alpha6beta1 modulation of PI3K and Cdc42 activities induces dynamic filopodium formation in human platelets

Platelets are an ideal model for studying a rapid morphological change in response to various signal transduction systems. Morphological changes via the activation of integrin alphaIIbbeta3 in platelets have been investigated intensively. In contrast, activation via integrin alpha6beta1 is less well studied. Here, we provide the first biochemical evidence that integrins alpha6beta1 and alphaIIbbeta3 of platelets are associated with different membrane proteins. We also demonstrate that platelets activated by integrin alpha6beta1 show dynamic change by actively forming filopodia and never fully spreading over a period of more than an hour. In addition, platelets activated by integrin alpha6beta1 are different from those activated by integrin alphaIIbbeta3 in terms of cell-substrate contact and in their distribution pattern of actin, Arp2/3 and various phosphotyrosine proteins. The morphological appearance of platelets produced through integrin alpha6beta1 activation is highly dependent on PI3 kinase (PI3K) but less dependent on Src kinase. Suppression of PI3K activity in integrin alpha6beta1 activated platelets induces an increase in Cdc42 activity and more filopodium formation. However, both Cdc42 and PI3K activity are higher in platelets activated by integrin alpha6beta1 than in those activated by integrin alphaIIbbeta3. Taken together, this study demonstrates that the signals induced by integrin alpha6beta1 modulate at the level of PI3K and Cdc42 activity to allow platelets to actively form filopodia.

PI3-kinase is essential for ADP-stimulated integrin alpha(IIb)beta3-mediated platelet calcium oscillation, implications for P2Y receptor pathways in integrin alpha(IIb)beta3-initiated signaling cross-talks

Phosphatidylinositol 3-kinase (PI3K) pathway is important for platelet activation. Recent studies showed that PI3K and oscillative calcium could cross talk to each other and positively regulate integrin alpha (IIb)beta3-mediated outside-in signaling. However, the mechanism of this feedback regulation remains to be further characterized. Here we found that treatments of both PI3K inhibitor wortmannin and P2Y1 inhibitor A3P5P could inhibit granular secretion in platelets. Additionally, when RGD-substrate adherent platelets were treated with the ADP scavenger apyrase to deplete the granular-released ADP, their attachments in engaging with substrates became looser and the frequency of calcium oscillation decreased. Since it is known that ADP stimulates the PI3K and calcium signal primarily through P2Y12 and P2Y1 receptors respectively, our data indicated that integrin alpha(IIb)beta3 downstream PI3K and calcium activation might be not completely coupled to integrin associated signaling complex, but in part through feedback stimulation by granular released ADP. Our data indicates the important roles of PI3K and granular released ADP in coordinating the feedback regulations in integrin alpha(IIb)beta3-mediated platelet activation.

Calcium oscillation and phosphatidylinositol 3-kinase positively regulate integrin alpha(IIb)beta3-mediated outside-in signaling

The frequency of calcium oscillation reveals the platelet activation status, however, the biological significance of the periodic calcium responses and methods of communication with other integrin-mediated signals are not clear. RGD-containing disintegrin rhodostomin coated substrates were employed to enhance platelet spreading and calcium oscillation through direct binding and clustering of the receptor integrin alpha(IIb)beta3. The results showed that the activation of phosphatidylinositol 3-kinase (PI3-K) and internal calcium pathways were crucial for alpha(IIb)beta3 outside-in signaling. PI3-K antagonists wortmannin and LY294002 inhibited disintegrin substrates and induced platelet spreading and calcium oscillation. At the same time, pretreatment of platelets with the microsomal calcium-ATPase inhibitor thapsigargin to deplete internal calcium stores severely impaired the calcium oscillation as well as PI3-K activation and spreading on disintegrin substrates. Because inhibition of one pathway could inhibit the other, our data indicates that PI3-K and calcium oscillation are synergistically operated and form a positive-feedback regulation in integrin alpha(IIb)beta3-mediated outside-in signaling.

Distinct glycoprotein Ib/V/IX and integrin alpha IIbbeta 3-dependent calcium signals cooperatively regulate platelet adhesion under flow

We have investigated the calcium signaling relationship between the two major platelet adhesion receptors, glycoprotein Ib/V/IX (GPIb/V/IX) and integrin alpha(IIb)beta(3), involved in regulating platelet adhesion on von Willebrand factor (vWf) under flow. Our studies demonstrate that GPIb engagement of immobilized vWf elicits a transient calcium spike that may function to promote reversible arrest of translocating platelets. Subsequent integrin alpha(IIb)beta(3) engagement of vWf promotes sustained calcium oscillations that are essential for the maintenance of irreversible adhesion. GPIb-induced calcium spikes appear distinct from those initiated by integrin alpha(IIb)beta(3), in that the former are exclusively mediated through release of intracellular calcium stores via a signaling mechanism independent of PI 3-kinase. In contrast, integrin alpha(IIb)beta(3)-dependent calcium flux involves a PI 3-kinase-dependent signaling mechanism linked to intracellular calcium mobilization and subsequent transmembrane calcium influx. Studies employing the caged calcium chelator (o-nitrophenyl-EGTA) demonstrate that transient calcium spikes initiate a transient phase of platelet arrest that is converted to irreversible adhesion with the development of sustained oscillatory calcium flux. These studies demonstrate the existence of a dual step calcium signaling mechanism utilized by GPIb and integrin alpha(IIb)beta(3) that serves to regulate the dynamics of platelet adhesion under flow.

Positional importance of Pro53 adjacent to the Arg49-Gly50-Asp51 sequence of rhodostomin in binding to integrin alphaIIbbeta3

Rhodostomin (RHO), a disintegrin isolated from snake venom, has been demonstrated to inhibit platelet aggregation through interaction with integrin alphaIIbbeta3, but there is a lack of direct evidence for RHO-integrin alphaIIbbeta3 binding. In addition, no study on the length of Arg(49)-Gly(50)-Asp(51) (RGD) loop of RHO influencing on its binding to integrin alphaIIbbeta3 has been reported. In the present study we have developed a highly sensitive dot-blot and glutathione S-transferase-RHO pull-down assays; the latter was coupled with a biotin-avidin-horseradish peroxidase enhanced-chemiluminescence detection system. These were able to demonstrate the direct binding of RHO to integrin alphaIIbbeta3. The pull-down assay further showed that four alanine-insertion mutants upstream of the RGD motif and three insertions downstream of the RGD were able to decrease integrin alphaIIbbeta3 binding activity to only a limited extent. By contrast, two insertions immediately next to RGD and one insertion in front of the Cys(57) caused almost complete loss of binding activity to alphaIIbbeta3. The results of the platelet-aggregation-inhibition assay and platelet-adhesion assay for the insertion mutants were consistent with results of the pull-down assay. It is thus concluded that, although an insertion of a single alanine residue in many positions of the RGD loop has only minor effects on RHO binding to integrin alphaIIbbeta3, the specific position of Pro(53) residue adjacent to the RGD sequence is important for RHO binding to platelet integrin alphaIIbbeta3.

Expression in Pichia pastoris and characterization by circular dichroism and NMR of rhodostomin

Rhodostomin (Rho) is a snake venom protein isolated from Calloselasma rhodostoma. Rho is a disintegrin that inhibits platelet aggregation by blocking the binding of fibrinogen to the integrin alpha(IIb)beta3 of platelets. Rho produced in Escherichia coli inhibited platelet aggregation with a K(I) value of 263 nM. Although functional, Rho produced in E. coli is misfolded based on our 2D and 3D NMR studies. In order to correct the folding problem, Rho was expressed in Pichia pastoris. The recombinant Rho expressed in P. pastoris inhibited platelet aggregation with a resulting K(I) value of 70 nM. This is the same potency as that of native Rho. CD analysis showed that the secondary structures of Rho are pH-independent and contain 3.5-7.9% alpha-helix, 48.2-50.5% beta-structures, and 42.3-47% coil. The sequential assignment and structure analysis of Rho were obtained using 2D and 3D 15N-edited NMR spectra. These results provide the first direct evidence that highly disulfide-bonded disintegrin can be expressed in P. pastoris with the correct fold. This evidence may serve as the basis for exploring the structure and function relationships as well as the dynamics of disintegrin and its variants.

Modification with a phosphorylation tag of PKA in the TraT-based display vector of Escherichia coli

We have previously developed the TraT display system to express the preS1 peptide of human hepatitis B virus (HBV) and the snake venom rhodostomin (RHO) on the surface of Escherichia coli. In this study, we modified the pT2 vector by adding a thrombin cutting site and a phosphorylation tag of protein kinase A before the multiple restriction enzyme sites. The modified vector allowed us to label the TraT fusion protein (TraT-RHO) with [32P] and to increase the detection sensitivity of TraT-RHO expression bacteria binding to and being internalized into BHK-21 cells. After the thrombin cleavage, the isotope labeled RHO could be detected in a free form. We therefore suggest that the new version of pT2 vector, pT2-KL, will facilitate to identify the counterpart of displayed peptide.

Receptor-mediated endocytosis as a selection force to enrich bacteria expressing rhodostomin on their surface

Previously, we developed a TraT display system to express snake venom rhodostomin (RHO), a disintegrin, on the external surface of Escherichia coli [J Biomed Sci 6:64-70;1999]. To show a new potential use of the TraT display system, we employed a biotin labeling technique coupled with SDS-PAGE and flow cytometry analyses to further demonstrate and confirm the expression of TraT-RHO on the E. coli surface. We also showed that the expression of TraT-RHO on the cell surface not only facilitated the bacteria adhesion to BHK-21 cells but also induced bacterial internalization into BHK-21 cells. This feature allowed us to enrich the TraT-RHO expression bacteria about 10,000-fold starting with a mixture of TraT-RHO bacteria with beta-galactosidase-positive bacteria in a ratio of 10(2):10(7) through four cycles of BHK-21 cell endocytosis and replating of engulfed bacteria on agar plates. We therefore suggest that the TraT display system can be applied to select out bacteria expressing a specific peptide sequence from a large population of display library through the process of receptor-mediated endocytosis and reamplification cycles.

DNA vaccination using the fragment C of botulinum neurotoxin type A provided protective immunity in mice

Botulinum neurotoxin (BoNT) is one of the most toxic substances known to produce severe neuromuscular paralysis. The currently used vaccine is prepared mainly from biohazardous toxins. Thus, we studied an alternative method and demonstrated that DNA immunization provided sufficient protection against botulism in a murine model. A plasmid of pBoNT/A-Hc, which encodes the fragment C gene of type A botulinum neurotoxin, was constructed and fused with an Igkappa leader sequence under the control of a human cytomegalovirus promoter. After 10 cycles of DNA inoculation with this plasmid, mice survived lethal doses of type A botulinum neurotoxin challenges. Immunized mice also elicited cross-protection to the challenges of type E botulinum neurotoxin. This is the first study demonstrating the potential use of DNA vaccination for botulinum neurotoxins.