Molecular Characterization and Functional Analysis of the Nattectin-like Toxin from the Venomous Fish Thalassophryne maculosa

TmC4-47.2 is a toxin with myotoxic activity found in the venom of Thalassophryne maculosa, a venomous fish commonly found in Latin America whose envenomation produces an injury characterized by delayed neutrophil migration, production of major pro-inflammatory cytokines, and necrosis at the wound site, as well as a specific systemic immune response. However, there are few studies on the protein structure and functions associated with it. Here, the toxin was identified from the crude venom by chromatography and protein purification systems. TmC4-47.2 shows high homology with the Nattectin from Thalassophryne nattereri venom, with 6 cysteines and QPD domain for binding to galactose. We confirm its hemagglutinating and microbicide abilities independent of carbohydrate binding, supporting its classification as a nattectin-like lectin. After performing the characterization of TmC4-47.2, we verified its ability to induce an increase in the rolling and adherence of leukocytes in cremaster post-capillary venules dependent on the α5β1 integrin. Finally, we could observe the inflammatory activity of TmC4-47.2 through the production of IL-6 and eotaxin in the peritoneal cavity with sustained recruitment of eosinophils and neutrophils up to 24 h. Together, our study characterized a nattectin-like protein from T. maculosa, pointing to its role as a molecule involved in the carbohydrate-independent agglutination response and modulation of eosinophilic and neutrophilic inflammation.

Kinetics of Influenza A/BANGKOK/1/1979(Н3N2) Virus Thermal Inactivation in the Presence of Polyallylamine

Polyelectrolytes currently play an increasingly important role in antivirus therapy. Antiviral activity towards influenza virus, measles virus, herpes simplex virus type 1, and cytomegalovirus was demonstrated for the 6000 Da polyelectrolyte polyallylamine. A nontoxic polyallylamine concentration of 30 µM at which the compound retains its antiviral effect towards measles and influenza viruses but lacks any toxic effect on human cells was previously determined. It is well known, at the same time, that simultaneous virus exposure to physical environmental factors and chemical substances causes a more significant decrease in virus infectivity. Temperature is among these physical factors since thermal exposure causes virus inactivation. Analysis of virus thermal inactivation parameters is of high practical importance when it comes to the development of vaccines against influenza virus and to the study of how virus particles infectivity decreases on various surfaces. In this view, the study of kinetic and thermodynamical characteristics of influenza virus thermal inactivation in the presence of the antiviral preparation polyallylanime is of particular interest. The paper reports that thermal inactivation of influenza virus in the temperature range of 38-60°C in the presence of polyallylamine follows the first-order reaction kinetics. Thermodynamic parameters of influenza virus thermal inactivation evidence that influenza virus surface proteins are involved in the inactivation process as a result of their interaction with polyallylamine. The obtained results show that polyallylamine may be used to accelerate thermal inactivation of the influenza virus.

Identification of Echinacea Purpurea (L.) Moench Root LysM Lectin with Nephrotoxic Properties

Echinacea purpurea (L.) Moench (EP) is a well-studied plant used for health benefits. Even though there are a lot of data on EP secondary metabolites, its active proteins are not studied well enough. The aim of our experiment was to purify lectin fraction from EP roots and evaluate its biological activity in vitro as well as its effect on kidney morphology in vivo. An EP root glycoprotein fraction was purified by affinity chromatography, identified by LC-MS/MS, and used for biological activity tests in vitro and in vivo. Identified glycoproteins were homologous with the LysM domain containing lectins from the Asteraceae plants Helianthus annuus L., Lactuca sativa L., Cynara cardunculus L. A purified fraction was tested by hemagglutination and hemagglutination inhibition (by carbohydrate reactions) in vitro. We purified the hemagglutinating active ~40 kDa size lactose, D-mannose, and D-galactose specific glycoproteins with two peptidoglycan binding LysM (lysine motif) domains. Purified LysM lectin was tested in vivo. Eight-week old Balb/C male mice (n = 15) were treated with 5 μg of the purified lectin. Injections were repeated four times per week. At the fifth experimental week, animals were sedated with carbon dioxide, then euthanized by cervical dislocation and their kidney samples were collected. Morphological changes were evaluated in hematoxylin and eosin stained kidney samples. The purified LysM lectin induced a statistically significant (p < 0.05) kidney glomerular vacuolization and kidney tubular necrosis (p < 0.001).

Structure and function analysis of Polygonatum cyrtonema lectin by site-directed mutagenesis

The crystal structure of mature Polygonatum cyrtonema lectin (PCL) showed three similar carbohydrate-binding sites (CBS I, CBS II, and CBS III). The Gln58 and Asp60 residues of CBS II are substituted with His58 and Asn60. To establish the relationship between the key amino acid residues and structure or activity of PCL, we constructed four recombinant mutants in CBS I, CBS II, and CBS III. The experimental results indicate that CBS I, CBS III and the disulfide bond play vital roles in the binding with mannose. Furthermore, molecular dynamics simulations and binding free energy calculation illustrate that CBS I has a direct and strong relationship with the activity of PCL. CBS II does not play a critical role in the model for mannose binding by PCL. Although CBS III does not enhance the activity, it helps to maintain the activity and 3D structure. These results suggest that the carbohydrate-binding site of PCL may be in a hydrophilic environment, and Asn and Tyr are the key amino acids involved in its binding with sugar, but Gln and Asp are not necessary to maintain its activity.

Conformational study reveals amino acid residues essential for hemagglutinating and anti-proliferative activities of Clematis montana lectin

Clematis montana lectin (CML), a novel mannose-binding lectin purified from C. montana Buch.-Ham stem (Ranunculaceae), has been proved to have hemagglutinating activity in rabbit erythrocytes and apoptosis-inducing activity in tumor cells. However, the biochemical properties of CML have not revealed and its structural information still needs to be elucidated. In this study, it was found that CML possessed quite good thermostability and alkaline resistance, and its hemagglutinating activity was bivalent metal cation dependent. In addition, hemagglutination test and fluorescence spectroscopy proved that GuHCl, urea, and sodium dodecyl sulfate could change the conformation of CML and further caused the loss of hemagglutination activity. Moreover, the changes of fluorescence spectrum indicated that the tryptophan (Trp) microenvironment conversion might be related to the conformation and bioactivities of CML. In addition, it was also found that Trp residues, arginine (Arg) residues, and sulfhydryl were important for the hemagglutinating activity of CML, but only Trp was proved to be crucial for the CML conformation. Furthermore, the Trp, Arg, and sulfhydryl-modified CML exhibited 97.17%, 76.99%, and 49.64% loss of its anti-proliferative activity, respectively, which was consistent with the alterations of its hemagglutinating activity. Given these findings, Trp residues on the surface of CML are essential for the active center to form substrate-accessible conformation and suitable environment for carbohydrate binding.

Hemagglutination by murine hepatitis viruses. Absence of detectable activity in strains 3, A59, and S grown on DBT cells

Erythrocytes from twelve mammalian and avian sources in ten different buffers at three incubation temperatures could not be hemagglutinated with murine hepatitis virus (MHV) strains 3, A59, or S grown on DBT cells. Viral antigen preparation in the absence of fetal calf serum, partial virus purification, or various concentrations of red blood cells still failed to yield detectable hemagglutinating activity. Thus, the newly described MHV-DVIM remains the only hemagglutinating strain of murine coronavirus.

Identification and location of the structural glycoproteins of a tissue culture-adapted turkey enteric coronavirus

The Minnesota strain of turkey enteric coronavirus (TCV) was grown on a human rectal tumor (HRT-18) cell line in the presence of radiolabeled amino acids and glucosamine to analyse virion structural proteins. In addition to the 52,000 unglycosylated nucleocapsid protein, three major glycoprotein species were found to be associated with the viral envelope. A predominant glycosylated protein with a molecular weight of 22-24,000 represented the transmembrane matrix protein. Larger glycoproteins with apparent molecular weights of 180-200,000 (gp 200), 120-125,000 (gp 120) and 95-100,000 (gp 100) were associated to the characteristic large bulbous projections (peplomers) located at the surface of the virion. The gp 100 and gp 120 species apparently arose from a proteolytic cleavage of gp 200, as suggested by digestion studies with trypsin and chymotrypsin. An additional large glycoprotein with mol. wt. of 140,000 (gp 140), that behaved as a disulfide-linked dimer of a 66,000 molecule, was found to be associated to granular projections located near the base of the large peplomers. Digestion studies with trypsin, bromelain and pronase demonstrated that gp 140 was related to the hemagglutinating activity of the virus. An inner membranous sac or tongue-shaped structure could be visualized in the interior of the viral particles following treatment with pronase. In contrast, trypsin or chymotrypsin treatments resulted in evaginations ("budding") on the virus surface. Progeny viral particles produced in TCV-infected cell cultures in the presence of tunicamycin lacked both types of surface projections, as demonstrated by electron microscopy and electrophoresis. The matrix protein also appeared to be reduced to its unglycosylated form, concomitant with a considerable loss of its antigenicity. Thus, with respect to its morphological and biochemical characteristics, TCV resembles viruses belonging to the group of mammalian hemagglutinating coronaviruses, but differs in that both types of envelope glycoproteins are N-glycosylated as in case of the avian infectious bronchitis virus.

Characteristics of a coronavirus causing vomition and wasting in pigs

Some characteristics of a virus, isolated from the tonsils of 2 pigs with clinical signs of inappetence and vomition and designated VW572 were examined. It induced the formation of syncytia in primary pig kidney cell cultures, caused hemadsorption and hemagglutination using chicken, turkey, rat and mouse erythrocytes. In growth curve experiments, infectious virus was produced intracellularly starting at 6 hours after inoculation and was followed by rapid release of the virus from the infected cells. The virus contains ribonucleic acid, is ether sensitive and has a size between 100 and 220 nm. At 37° C, the infectivity titer decreased about 2 log10TCID50 per 24 hours. The viral population was heterogeneous as indicated by the rate of inactivation by U.V. irradiation and acid pH. Some hemagglutinating activity was left after complete loss of infectivity by ether-, temperature- and U.V. treatment. The VW 572 isolate is antigenically related if not identical to isolates from Canada, U.S.A. and England which were classified as a porcine coronavirus.

Oronasal and intracerebral inoculation of the VW572 isolate in colostrum deprived pigs resulted in clinical disease after an incubation period of 6 and 4 days, respectively. Signs were characterized by depression, vomition, loss of appetence with rapid weakness in young pigs and vomition with progressive wasting in older pigs. Virus was isolated from nasal and pharyngeal swabs, nasal mucosa, tonsils, lungs and hind brains but not from rectal swabs or other organs tested. Virus could not be isolated later than 8 days after inoculation. Hemagglutination inhibiting and neutralizing antibodies were detected in sera at 6 days and 9 days after inoculation, respectively.