A peptide-model for the heparin-binding property of pseudorabies virus glycoprotein III

Antiviral activities of lactoferrin

Lactoferrin (LF) is an iron binding glycoprotein that is present in several mucosal secretions. Many biological functions have been ascribed to LF. One of the functions of LF is the transport of metals, but LF is also an important component of the non-specific immune system, since LF has antimicrobial properties against bacteria, fungi and several viruses. This review gives an overview of the present knowledge about the antiviral activities and, when possible, the antiviral modes of action of this protein. Lactoferrin displays antiviral activity against both DNA- and RNA-viruses, including rotavirus, respiratory syncytial virus, herpes viruses and HIV. The antiviral effect of LF lies in the early phase of infection. Lactoferrin prevents entry of virus in the host cell, either by blocking cellular receptors, or by direct binding to the virus particles.

Interaction of heparin with a synthetic pentadecapeptide from the C-terminal heparin-binding domain of fibronectin

The synthetic pentadecapeptide FN-C/H II (KNNQKSEPLIGRKKT-NH(2)) has the sequence of the carboxy-terminal heparin-binding domain of module III(14) of fibronectin. Interaction of FN-C/H II with bovine lung heparin has been studied by (1)H and (23)Na NMR spectroscopy and by heparin affinity chromatography. FN-C/H II binds to heparin from pD <2 up to pD approximately 10; at higher pD, the binding decreases as the lysine side-chain ammonium groups are titrated. Na(+) counterions are displaced from the counterion condensation volume that surrounds sodium heparinate by FN-C/H II, which provides direct evidence that the binding involves electrostatic interactions. The pK(A) values for each of the five ammonium groups of FN-C/H II increase upon binding to heparin which, together with chemical shift data, indicates that the binding involves both delocalized and direct electrostatic interactions between ammonium groups of FN-C/H II and carboxylate and/or sulfate groups of heparin. NMR data also provide evidence for the direct interaction of the guanidinium group of the arginine side chain with anionic sites on heparin. The affinity of heparin for FN-C/H II and for 13 analogue peptides in which lysine and arginine residues were systematically substituted with alanine increases as the number of basic residues increases. The relative contribution of each lysine and arginine to the affinity of heparin for FN-C/H II is R(12) > K(13) > K(14) > K(1) > K(5). Nuclear Overhauser enhancement (NOE) data indicate that, while FN-C/H II is largely unstructured in aqueous solution, the bound peptide interconverts among overlapping, turn-like conformations over the L(9) - T(15) segment of the peptide. NOE data for the interaction of FN-C/H II with a heparin-derived hexasaccharide, together with the number of Na(+) ions displaced from heparin by FN-C/H II as determined by (23)Na NMR, indicates that the peptide binds to a hexasaccharide segment of heparin. Identical NMR and heparin affinity chromatography results were obtained for the interaction of FN-C/H II and its D-amino acid analogue peptide with heparin, which is of interest for the potential use of peptides as therapeutic agents for diseases in which cell adhesion plays a critical role.

Identification of a linear heparin binding domain for human respiratory syncytial virus attachment glycoprotein G

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in infants and young children worldwide. Infection is mediated, in part, by an initial interaction between attachment protein (G) and a highly sulfated heparin-like glycosaminoglycan (Gag) located on the cell surface. Synthetic overlapping peptides derived from consensus sequences of the G protein ectodomain from both RSV subgroups A and B were tested by heparin-agarose affinity chromatography for their abilities to bind heparin. This evaluation identified a single linear heparin binding domain (HBD) for RSV subgroup A (184A-->T198) and B (183K-->K197). The binding of these peptides to Vero cells was inhibited by heparin. Peptide binding to two CHO cell mutants (pgsD-677 and pgsA-745) deficient in heparan sulfate or total Gag synthesis was decreased 50% versus the parental cell line, CHO-K1, and decreased an average of 87% in the presence of heparin. The RSV-G HBD peptides were also able to inhibit homologous and heterologous virus infectivity of Vero cells. These results indicate that the sequence 184A/183K-->198T/K197 for RSV subgroups A and B, respectively, defines an important determinant of RSV-G interactions with heparin.

Neuroinvasiveness of pseudorabies virus injected intracerebrally is dependent on viral concentration and terminal field density

Pseudorabies virus (PRV), a neurotropic swine alpha herpesvirus, has been used extensively for transneuronal analysis ofmultisynaptic circuitry after peripheral injection. In the present analysis, we examined the influence of viral concentration and neuronal architecture on the invasiveness, replication, and transynaptic passage of an attenuated strain of PRV (PRV-Bartha) injected into rat striatum. Different concentrations of PRV-Bartha were injected into the striatum at a constant rate of infusion (10 nl/minute), and animals were killed 50 hours later. Viral concentration was manipulated by either altering the volume of the inoculum (100, 50, 20 nl) or by diluting the inoculum within a constant volume of 100 nl. Immunohistochemical localization of infected neurons revealed dramatic differences in the progression of infection that were dependent directly on the concentration of injected virus. In every case, the pattern of infection was consistent with preferential uptake of virions by axon terminals and retrograde transynaptic passage of virus from the injection site. The known topographically organized corticostriatal projections permitted a precise definition of the zone of viral uptake. This analysis demonstrated that the "effective zone of viral uptake" (i.e., the zone within which viral uptake led to productive replication of virus) varied in relation to the concentration of injected virus, with the highest concentration of PRV invading terminals within a 500 microm radius of the canula. Concentration-dependent changes in the progression of retrograde transynaptic infection also were observed. The highest concentration of virus produced the most extensive infection. The distribution of infected neurons in these cases included those with known afferent projections to striatum as well as those that became infected by retrograde transynaptic infection. Lesser concentrations of PRV-Bartha produced an increasingly restricted infection of the same circuitry within the same postinoculation interval. It is noteworthy that neurons known to elaborate dense striatal terminal fields were less sensitive to reduction in viral concentration than those giving rise to terminal fields of lesser density. Collectively, the data indicate that the onset of viral replication after intracerebral injection of PRV is directly dependent on virus concentration and terminal field density at the site of virus injection.

Transneuronal tracing of neural pathways controlling an abdominal muscle, rectus abdominis, in the ferret

Abdominal muscles participate in generating a large number of behaviors and reflex responses, including expiration, coughing, sneezing, vomiting, postural control, production of speech, straining, facilitation of venous return to the heart, and reaction to vestibular stimulation. However, the only premotor neurons that have been conclusively shown to influence abdominal motoneurons are located in nucleus retroambiguus, the expiratory region of the caudal ventral respiratory group. In the present study, the neural circuitry controlling the activity of one abdominal muscle, rectus abdominis, was mapped using the transneuronal tracer pseudorabies virus (PRV) in the ferret. Injections of PRV into rectus abdominis labeled large presumed motoneurons in the ventral horn of T12-L4, and smaller presumed interneurons that were scattered in laminae VII, VIII, IX, and X of T4-L4. In addition, neurons in several areas of the medulla and caudal pons, including the retroambigual nucleus, medial and ventromedial reticular formation, nucleus prepositus hypoglossi, vestibular nuclei, and raphe nuclei, were infected by transynaptic passage of PRV from rectus abdominis motoneurons. Thus, the multifunctional roles of abdominal muscles appear to be coordinated by premotor neurons located in both the spinal cord and several regions of the brainstem.

Transmission, species specificity, and pathogenicity of Aujeszky's disease virus

Aujeszky's disease virus (ADV), also known as pseudorabies virus (PrV), is an alphaherpesvirus that causes fatal infections in a wide range of animal species. The virus shares a variety of biological properties with human pathogenic herpesviruses like herpes simplex virus or varicella-zoster virus. Although only limited data are available, it seems unlikely that PrV causes disease in immunocompetent humans, but may pose a risk for immunocompromised patients.

Glycoprotein B (gB) of pseudorabies virus interacts specifically with the glycosaminoglycan heparin

We have previously shown that the pseudorabies virus (PrV) glycoproteins gB and gC (former PrV-gII and PrV-gIII) exhibit heparin-binding properties. While PrV-gC functions as the major adsorption protein, the biological role of the heparin-binding properties of PrV-gB are not understood. We used a gC-deleted PrV-mutant, PrV (dlg92/dltk), to analyse the heparin-binding properties of PrV-gB and the biological role of the PrV-gB-protein in adsorption. PrV-gB was the only glycoprotein of this vaccine strain binding to immobilised heparin in in vitro assays. Presence of the gC-protein was not necessary for the interaction of gB with heparin. Soluble heparin also interfered with adsorption of this mutant virus to a similar extent as it blocked adsorption of wild-type PrV (Ka), but it had only a minor inhibitory effect on infectivity of the mutant strain. These results show that PrV-gB interacts specifically with immobilized heparin and heparin-like structures on the cell surface, but this interaction is not required for a productive infection.

The receptor-binding domain of pseudorabies virus glycoprotein gC is composed of multiple discrete units that are functionally redundant

Many herpesviruses attach to cells in a two-step process, using the glycoprotein gC family of homologs to bind the primary receptor, heparan sulfate (HS) proteoglycan, and glycoprotein gD homologs to bind an unknown secondary receptor. We have previously shown by deletion analysis that the amino-terminal one-third of gC from pseudorabies virus (PRV), a swine herpesvirus, includes at least the principal HS receptor-binding domain. This portion of PRV gC contains three discrete clusters of basic residues that exactly or nearly match proposed consensus sequences for heparin-binding domains (HBDs); four additional potential HBDs lie in the distal two-thirds of the glycoprotein. We now specifically implicate each of the three amino-terminal HBDs in virus attachment. Mutational analysis demonstrated that any one of the three HBDs could mediate efficient virus infectivity; HS-dependent PRV attachment to cells was eliminated only after all three amino-terminal HBDs were altered. Furthermore, the binding dysfunction was due to a disruption of the specific HBDs and not to total charge loss. Thus, unlike previously described viral receptor-binding domains, the PRV gC receptor-binding domain is composed of multiple, discrete units that can function independently of one another. These units may function redundantly either to increase binding affinity or perhaps to effectively increase the virus's host range.

Protein-glycosaminoglycan interactions: infectiological aspects

Glycosaminoglycans (GAGs) are linear heteropolysaccharides consisting of repeated disaccharide units that are variably N- and O-sulfated. Due to this heterogeneity, GAGs possess a high amount of structural information. Linked to a protein core to form a proteoglycan, GAGs are present on the surface of probably all mammalian tissues. During the recent years, a number of pathogens ranging from viruses to protozoans were found to interact specifically with cell surface GAGs to recognize and bind to their target cells. This review is intended to give a short overview over protein-GAG interaction under the aspects of infection.

Interaction of herpes simplex virus glycoprotein gC with mammalian cell surface molecules

The entry of herpes simplex virus (HSV) into mammalian cells is a multistep process beginning with an attachment step involving glycoproteins gC and gB. A second step requires the interaction of glycoprotein gD with a cell surface molecule. We explored the interaction between gC and the cell surface by using purified proteins in the absence of detergent. Truncated forms of gC and gD, gC1(457t), gC2(426t), and gD1(306t), lacking the transmembrane and carboxyl regions were expressed in the baculovirus system. We studied the ability of these proteins to bind to mammalian cells, to bind to immobilized heparin, to block HSV type 1 (HSV-1) attachment to cells, and to inhibit plaque formation by HSV-1. Each of these gC proteins bound to conformation-dependent monoclonal antibodies and to human complement component C3b, indicating that they maintained the same conformation of gC proteins expressed in mammalian cells. Biotinylated gC1(457t) and gC2(426t) each bind to several cell lines. Binding was inhibited by an excess of unlabeled gC but not by gD, indicating specificity. The attachment of gC to cells involves primarily heparan sulfate proteoglycans, since heparitinase treatment of cells reduced gC binding by 50% but had no effect on gD binding. Moreover, binding of gC to two heparan sulfate-deficient L-cell lines, gro2C and sog9, both of which are mostly resistant to HSV infection, was markedly reduced. Purified gD1 (306t), however, bound equally well to the two mutant cell lines. In contrast, saturating amounts of gC1(457t) interfered with HSV-1 attachment to cells but failed to block plaque formation, suggesting a role for gC in attachment but not penetration. A mutant form of gC lacking residues 33 to 123, gC1(delta 33-123t), expressed in the baculovirus system, bound significantly less well to cells than did gC1(457t) and competed poorly with biotinylated gC1(457t) for binding. These results suggest that residues 33 to 123 are important for gC attachment to cells. In contrast, both the mutant and wild-type forms of gC bound to immobilized heparin, indicating that binding of these proteins to the cell surface involves more than a simple interaction with heparin. To determine that the contribution of the N-terminal region of gC is important for HSV attachment, we compared several properties of a mutant HSV-1 which contains gC lacking amino acids 33 to 123 to those of its parental virus, which contains full-length gC. The mutant bound less well to cells than the parental virus but exhibited normal growth properties.(ABSTRACT TRUNCATED AT 400 WORDS)

A heterologous heparin-binding domain can promote functional attachment of a pseudorabies virus gC mutant to cell surfaces

The efficient attachment of pseudorabies virus to cultured cells is dependent on an electrostatic interaction between negatively charged cell surface heparan sulfate and the viral envelope glycoprotein gC. Deletion of the first one-third of gC severely impairs virus attachment, but the mutant virions are still capable of entering cells and establishing an infection via a gC-independent pathway. This region of gC contains three clusters of positively charged amino acids that exactly or nearly conform to proposed consensus motifs for heparin-binding domains (HBDs), and the loss of one or more of these potential HBDs may be responsible for the observed attachment defect. To more directly show the involvement of HBDs in pseudorabies virus attachment to cells, we replaced the first one-third of gC with a single, biochemically defined HBD from apolipoprotein B-100. On the basis of the results of attachment, penetration, and heparin competition assays, the heterologous HBD mediated heparan sulfate-dependent virus attachment, but not to fully wild-type levels. Although the intermediate phenotype is not understood, the apolipoprotein B-100 HBD may represent the smallest defined amino acid sequence that promotes functional herpesvirus attachment to cultured cells.