The basement membrane glycoprotein entactin promotes cell attachment and binds calcium ions

Mouse entactin derived from the extracellular matrix of M1536-B3 cells and from insect cells infected with a recombinant virus containing entactin sequences were shown to promote the attachment of mouse mammary tumor, human melanoma, and other cells. The cell attachment was inhibited by antibodies against mouse entactin but not by anti-fibronectin or anti-laminin antibodies. On a weight basis entactin was as effective as laminin in promoting the attachment of mouse mammary tumor cells. The attachment of cells to entactin was in part mediated by the integrin recognition RGD peptide sequence. This was demonstrated by the cell attachment properties of peptides derived from entactin which contained this sequence. Furthermore, the peptide RGDS could inhibit the attachment of mouse mammary tumor cells to entactin to approximately 60% of control. It is suggested that additional cell recognition sequences may be present in entactin. The direct binding of calcium ions to entactin was observed. It is probable that the binding sites reside in peptide sequences located toward the NH2 terminus region of entactin. This conclusion was supported by the demonstration that synthetic peptides, containing potential calcium binding sequences derived from entactin, bound calcium. In addition, a recombinant peptide containing the amino-terminal 330 amino acids of entactin also bound calcium ions. The significance of these properties of entactin is discussed.     

Proteoglycans Act as Cellular Hepatitis Delta Virus Attachment Receptors

The hepatitis delta virus (HDV) is a small, defective RNA virus that requires the presence of the hepatitis B virus (HBV) for its life cycle. Worldwide more than 15 million people are co-infected with HBV and HDV. Although much effort has been made, the early steps of the HBV/HDV entry process, including hepatocyte attachment and receptor interaction are still not fully understood. Numerous possible cellular HBV/HDV binding partners have been described over the last years; however, so far only heparan sulfate proteoglycans have been functionally confirmed as cell-associated HBV attachment factors. Recently, it has been suggested that ionotrophic purinergic receptors (P2XR) participate as receptors in HBV/HDV entry. Using the HBV/HDV susceptible HepaRG cell line and primary human hepatocytes (PHH), we here demonstrate that HDV entry into hepatocytes depends on the interaction with the glycosaminoglycan (GAG) side chains of cellular heparan sulfate proteoglycans. We furthermore provide evidence that P2XR are not involved in HBV/HDV entry and that effects observed with inhibitors for these receptors are a consequence of their negative charge. HDV infection was abrogated by soluble GAGs and other highly sulfated compounds. Enzymatic removal of defined carbohydrate structures from the cell surface using heparinase III or the obstruction of GAG synthesis by sodium chlorate inhibited HDV infection of HepaRG cells. Highly sulfated P2XR antagonists blocked HBV/HDV infection of HepaRG cells and PHH. In contrast, no effect on HBV/HDV infection was found when uncharged P2XR antagonists or agonists were applied. In summary, HDV infection, comparable to HBV infection, requires binding to the carbohydrate side chains of hepatocyte-associated heparan sulfate proteoglycans as attachment receptors, while P2XR are not actively involved.     

Rabies virus binding to an acetylcholine receptor alpha-subunit peptide

The binding of 125I-labeled rabies virus to a synthetic peptide comprising residues 173-204 of the alpha 1-subunit of the nicotinic acetylcholine receptor was investigated. Binding of rabies virus to the receptor peptide was dependent on pH, could be competed with by unlabeled homologous virus particles, and was saturable. Synthetic peptides of snake venom, curaremimetic neurotoxins and of the structurally similar segment of the rabies virus glycoprotein, were effective in competing with labeled virus binding to the receptor peptide at micromolar concentrations. Similarly, synthetic peptides of the binding domain on the acetylcholine receptor competed for binding. These findings suggest that both rabies virus and neurotoxins bind to residues 173-204 of the alpha 1-subunit of the acetylcholine receptor. Competition studies with shorter alpha-subunit peptides within this region indicate that the highest affinity virus binding determinants are located within residues 179-192. A rat nerve alpha 3-subunit peptide, that does not bind alpha-bungarotoxin, inhibited binding of virus to the alpha 1 peptide, suggesting that rabies binds to neuronal nicotinic acetylcholine receptors. These studies indicate that synthetic peptides of the glycoprotein binding domain and of the receptor binding domain may represent useful antiviral agents by targeting the recognition event between the viral attachment protein and the host cell receptor, and inhibiting attachment of virus to the receptor.     

A recombinant, arginine-glycine-aspartic acid (RGD) motif from foot-and-mouth disease virus binds mammalian cells through vitronectin and, to a lower extent, fibronectin receptors

The cell-binding abilities of a recombinant, RGD-containing peptide from foot-and-mouth disease virus (FMDV) have been characterized in HeLa and BHK cells. This peptide represents the aa sequence of the solvent-exposed G-H loop of protein VP1 which is involved in cell recognition and infection. The efficiency of the viral motif in promoting cell attachment and spreading is comparable to that shown by fibronectin or vitronectin. Cell binding is inhibited by a monoclonal antibody directed against a viral, RGD-involving B-cell epitope and also by sera against vitronectin (_Vβ₃/β₅) and fibronectin (₅β₁) receptors. In addition, a synthetic RGD peptide, which is a ligand for both integrins, prevents the cell binding mediated by the FMDV domain. These data demonstrate that the FMDV RGD motif is a potent ligand for cell-receptor integrins and sufficient to promote cell attachment to susceptible cells mainly through the vitronectin receptor.     

Hepatitis B virus large surface protein is not secreted but is immunogenic when selectively expressed by recombinant vaccinia virus.

The envelope region of the hepatitis B virus (HBV) genome contains an open reading frame that begins upstream of the major surface protein gene. The two minor proteins that are initiated within this pre-s segment are immunogenic and may be involved in virus attachment to hepatocytes. We have constructed a recombinant vaccinia virus that contains the predicted coding segment for the large surface protein (LS) under control of a vaccinia virus that contains the predicted coding segment for the large surface protein (LS) under control of a vaccinia virus promoter. Cells infected with the recombinant virus synthesized HBV polypeptides of 39 and 42 kilodaltons, corresponding to the unglycosylated and glycosylated forms of LS, respectively. The presence of pre-s epitopes in the 39- and 42-kilodalton polypeptides was demonstrated by binding of antibody prepared against a synthetic peptide. Synthesis of the 42-kilodalton species was specifically inhibited by tunicamycin, suggesting that it is N-glycosylated. Despite apparent glycosylation, LS was not secreted into the medium of infected cells. Nevertheless, rabbits vaccinated with the purified recombinant virus made antibodies that recognized s and pre-s epitopes. Antibody to the NH2 terminus of LS appeared before or simultaneously with antibody that bound to the major surface protein. The additional immunogenicity provided by expression of LS may be advantageous for the development of an HBV vaccine.     

Synergism between membrane gangliosides and Arg-Gly-Asp-directed glycoprotein receptors in attachment to matrix proteins by melanoma cells

The identification of specific cell surface glycoprotein receptors for Arg-Gly-Asp-containing extracellular matrix proteins such as fibronectin has focused attention on the role of gangliosides in this process. Is their involvement dependent or independent of the protein receptors? In attachment assays with cells from a human melanoma cell line, titration experiments with an antibody (Mel 3) with specificity for the disialogangliosides GD2 and GD3, used together with a synthetic peptide containing the cell binding sequence Arg-Gly-Asp, show that their joint effect is synergistic. Both the Mel 3 antibody and the synthetic peptide individually cause rapid detachment of melanoma cells from fibronectin substrate but, when used together, much smaller concentrations of both are required to achieve the same effect. The Mel 3 antibody was not nonspecifically reducing receptor binding to the Arg- Gly-Asp sequence since, in binding assays with radiolabeled peptide performed with cells in suspension, very little peptide is bound by the melanoma cells under these conditions but addition of Mel 3, an antibody of IgM isotype, causes a two- to threefold increase in specific binding. The simplest interpretation of these data is that the Mel 3 antibody is causing sufficient clustering of membrane gangliosides in local areas and producing a favorably charged environment to facilitate peptide binding by specific glycoprotein receptors.     

Apolipoprotein E Mediates Attachment of Clinical Hepatitis C Virus to Hepatocytes by Binding to Cell Surface Heparan Sulfate Proteoglycan Receptors

Our previous studies demonstrated that the cell culture-grown hepatitis C virus of genotype 2a (HCVcc) uses apolipoprotein E (apoE) to mediate its attachment to the surface of human hepatoma Huh-7.5 cells. ApoE mediates HCV attachment by binding to the cell surface heparan sulfate (HS) which is covalently attached to the core proteins of proteoglycans (HSPGs). In the present study, we further determined the physiological importance of apoE and HSPGs in the HCV attachment using a clinical HCV of genotype 1b (HCV1b) obtained from hepatitis C patients and human embryonic stem cell-differentiated hepatocyte-like cells (DHHs). DHHs were found to resemble primary human hepatocytes. Similar to HCVcc, HCV1b was found to attach to the surface of DHHs by the apoE-mediated binding to the cell surface HSPGs. The apoE-specific monoclonal antibody, purified HSPGs, and heparin were all able to efficiently block HCV1b attachment to DHHs. Similarly, the removal of heparan sulfate from cell surface by treatment with heparinase suppressed HCV1b attachment to DHHs. More significantly, HCV1b attachment was potently inhibited by a synthetic peptide derived from the apoE receptor-binding region as well as by an HSPG-binding peptide. Likewise, the HSPG-binding peptide prevented apoE from binding to heparin in a dose-dependent manner, as determined by an in vitro heparin pull-down assay. Collectively, these findings demonstrate that HSPGs serve as major HCV attachment receptors on the surface of human hepatocytes to which the apoE protein ligand on the HCV envelope binds.     

ICAM-2 peptides mediate lymphocyte adhesion by binding to CD11a/CD18 and CD49d/CD29 integrins.

Three fifteen-amino-acid polypeptides designated peptides 1, 2 and 3 were synthesised as likely candidates for mimicking the role of ICAM-2 as a ligand. The ability of each peptide to bind lymphoid cells was tested. Peptide 2 largely mediated cell attachment of unstimulated cells and this binding was only marginally increased by stimulating the cells with phorbol dibutyrate (P(Bu)2). Peptide 3 mediated minimal spontaneous cell attachment, but this binding was significantly enhanced following P(Bu)2 stimulation. Peptide 1 had no effect on cell attachment with or without stimulation. The cell attachment to peptide 2 was both temperature- and cation-dependent. Studies using specific monoclonal antibodies showed that with unstimulated cells, anti-VLA-4 alpha(CD49d) or beta chain (CD29) antibodies (KD4-13 and 4B4) and anti-CD18 (1B4) each partially inhibited the cell binding. Monoclonal antibodies against CD54 (ICAM-1; 84H10 or LB2), MHC class 1 (W6/32) and control mouse IgG had no effect. When anti-CD29 and anti-CD18 monoclonal antibodies were used concurrently, there was almost complete inhibition of the cell attachment. These observations indicated that cell adhesion via ICAM-2 is mediated: (i) predominantly by peptide 2 in unstimulated and P(Bu)2-stimulated cells, and also, to some extent, by peptide 3 in P(Bu)2-stimulated cells and (ii) by binding to both CD11/CD18 and CD49d/CD29 integrins.     

Cloning and expression of a novel hepatitis B virus-binding protein from HepG2 cells

A direct involvement of the hepatitis B virus (HBV) preS1-(21-47) sequence in virus attachment to cell membrane receptor(s) and the presence on the plasma membranes of HepG2 cells of protein(s) with receptor activity for HBV have been suggested by many previous experiments. In this study, by using a tetravalent derivative of the preS1-(21-47) sequence, we have isolated by affinity chromatography from detergent-solubilized HepG2 plasma membranes a 44-kDa protein (HBV-binding protein; HBV-BP), which was found to closely correspond to the human squamous cell carcinoma antigen 1 (SCCA1), a member of the ovalbumin family of serine protease inhibitors. Comparison of SCCA1 sequence with the sequence of the corresponding HBV-BP cDNA, cloned by polymerase chain reaction starting from RNA poly(A)(+) fractions extracted from HepG2 cells, indicated the presence of only four nucleotide substitutions in the coding region, leading to three amino acid changes. Intact recombinant HBV-BP lacked inhibitory activity for serine proteases such as alpha-chymotrypsin and trypsin but inhibited with high potency cysteine proteases such as papain and cathepsin L. Direct binding experiments confirmed the interaction of recombinant HBV-BP with the HBV preS1 domain. HepG2 cells overexpressing HBV-BP after transfection of corresponding cDNA showed a virus binding capacity increased by 2 orders of magnitude compared with untransfected cells, while Chinese hamster ovary cells, which normally do not bind to HBV, acquired susceptibility to HBV binding after transfection. Native HBV particle entry was enhanced in transfected cells. Both recombinant HBV-BP and antibodies to recombinant HBV-BP blocked virus binding and internalization in transfected cells as well as in primary human hepatocytes in a dose-dependent manner. Our findings suggest that this protein plays a major role in HBV infection.     

Preliminary characterization of an epitope involved in neutralization and cell attachment that is located on the major bovine rotavirus glycoprotein.

The 38,200-molecular weight (unreduced)/41,900-molecular-weight (reduced) glycoprotein of bovine rotavirus, isolate C486, was identified as the major neutralizing antigen. This glycoprotein as well as the corresponding glycoprotein of another bovine rotavirus serotype also specifically attached to cell monolayers under normal conditions for virus adsorption in vitro. Further support for this glycoprotein being directly responsible for virus attachment to cells was that (i) infectious virus of both serotypes could compete with the C486 glycoprotein for cell surface receptors, and (ii) neutralizing monospecific antiserum and neutralizing monoclonal antibodies directed toward the glycoprotein could block this virus-cell interaction. Preliminary epitope mapping of the glycoprotein with monoclonal antibodies further localized the neutralization-adsorption domain to a peptide with an approximate molecular weight of 14,000. The effect of two protein modifications, glycosylation and disulfide bridging, on the reactivity of this peptide with antibodies and cell surface receptors was investigated. It was demonstrated that, whereas glycosylation did not appear to affect these reactivities, disulfide bridging seemed to be essential.     

Immunogenic peptide comprising a mouse hepatitis virus A59 B-cell epitope and an influenza virus T-cell epitope protects against lethal infection.

The coronavirus spike protein S is responsible for important biological activities including virus neutralization by antibody, cell attachment, and cell fusion. Recently, we have elucidated the amino acid sequence of an S determinant common in murine coronaviruses (W. Luytjes, D. Geerts, W. Posthumus, R. Meloen, and W. Spaan, J. Virol. 63:1408-1412, 1989). A monoclonal antibody directed to this determinant (MAb 5B19.2) protected mice against acute fatal infection. In this study, BALB/c mice were immunized with a synthetic peptide of 13 amino acids corresponding to the binding site of MAb 5B19.2, which was either extended with an amino acid sequence of influenza virus hemagglutinin or conjugated to keyhole limpet hemocyanin. Both immunogens induced S-specific antibodies in mice, but only the hemagglutinin-peptide construct protected them against lethal challenge. In contrast to mouse hepatitis virus type 4 (MHV-4), MHV-A59 was not neutralized in vitro by MAb 5B19.2. Neither MHV-A59 nor MHV-4 was neutralized in vitro by antibodies comprising by the synthetic peptides. Our results demonstrated that antibodies elicited with a synthetic peptide comprising a B-cell epitope and a T-helper cell determinant can protect mice against an acute fetal mouse hepatitis virus infection.     

Multiple cell surface receptors for the short arms of laminin: alpha 1 beta 1 integrin and RGD-dependent proteins mediate cell attachment only to domains III in murine tumor laminin

Cell surface molecules that interact with the cross formed by the three short arms of murine tumor laminin were studied using thermal perturbation, antibody and peptide blocking, and affinity chromatography. Several potential receptors for the laminin short arms were revealed that differed from those mediating cell attachment to the E8 (long arm) fragment. Two cell lines, Rugli and L8 attached well to E1-X (short arm) fragments of laminin. This attachment was blocked by antibodies against alpha 1 integrin chains. Other cells were unable to attach strongly to E1-X, but attached to P1. This attachment was unaffected by anti-beta 1 integrin antibodies, but specifically blocked by the peptide GRGDS. By contrast, binding of Rugli cells was RGD independent and blocked by anti-beta 1 integrin antibodies. G7 and C2C12 myoblasts were very sensitive to GRGDS (ID50 approximately 2 micrograms.ml-1) for attachment to P1 which implied that a non-beta 1 series integrin, possibly alpha v beta 3, was involved. On heat denaturation of P1(3) attachment remained sensitive to RGDS and ID50 was unchanged. On heat denaturation of E1-X, attachment remained sensitive to RGDS but the ID50 increased to approximately 200 micrograms.ml-1. Cellular beta 1 integrins were retained on laminin affinity columns. A beta 1 integrin with an approximately 190 kD alpha-chain could be isolated from Rugli cells whose attachment could be blocked by anti-alpha 1 antibodies and not from cells blocked by RGDS peptides. Anti-alpha 1 antibodies blocked Rugli attachment to native laminin, but only when the E8 cell binding sites on laminin were also blocked. Thus, a receptor related to alpha 1 beta 1 integrin can function simultaneously with a receptor for E8. Anti-alpha 1 also blocked attachment to heated laminin, suggesting that the heat-stable attachment activity in laminin involved the E1-X binding site. Thus, at least two putative receptors mediate attachment to the short arms of laminin. One, related to alpha 1 beta 1 integrin, recognizes RGDS-independent sites in E1-X defined by P1 (within domains III, IIIa, IIIb), and one is an RGD-dependent molecule recognizing sites in P1, and is not a beta 1 integrin.     

Differential properties of attachment of human fibroblasts to various extracellular matrix proteins

Human diploid fibroblasts (TIG-3) were shown to attach and spread onto substrata coated with collagen, fibronectin, laminin and vitronectin. The cell attachment to these proteins required divalent cations. Mg2+ stimulated the cell attachment to all the proteins, while Ca2+ alone was not effective for the attachment to collagen and laminin. A mild trypsin treatment had prevented cells from attaching to the laminin, while it had no effect on the attachment to the other proteins. The fibronectin fragment, which retained cell binding activity, inhibited the cells from attaching and spreading onto fibronectin, but it did not cause any inhibition on the other proteins. The synthetic peptide GRGDSP inhibited the cells from attaching and spreading onto fibronectin and vitronectin, while it did not cause any inhibition on collagen and laminin. In attempts to isolate distinct receptors for these proteins, we were able to purify proteins very similar to the fibronectin and vitronectin receptors of human placenta. Based on the differential properties of the attachment of TIG-3 cells to these proteins and biochemical data, we indicate that human diploid fibroblasts have distinctive binding sites (receptors) for collagen, fibronectin, laminin and vitronectin.     

Identification of a peptide sequence involved in homophilic binding in the neural cell adhesion molecule NCAM

The neural cell adhesion molecule NCAM is capable of mediating cell-cell adhesion via homophilic interactions. In this study, three strategies have been combined to identify regions of NCAM that participate directly in NCAM-NCAM binding: analysis of domain deletion mutations, mapping of epitopes of monoclonal antibodies, and use of synthetic peptides to inhibit NCAM activity. Studies on L cells transfected with NCAM mutant cDNAs using cell aggregation and NCAM-covasphere binding assays indicate that the third immunoglobulin-like domain is involved in homophilic binding. The epitopes of four monoclonal antibodies that have been previously shown to affect cell-cell adhesion mediated by NCAM were also mapped to domain 3. Overlapping hexapeptides were synthesized on plastic pins and assayed for binding with these monoclonal antibodies. One of them (PP) reacted specifically with the sequence KYSFNY. Synthetic oligopeptides containing the PP epitope were potent and specific inhibitors of NCAM binding activity. A substratum containing immobilized peptide conjugates also exhibited adhesiveness for neural retinal cells. Cell attachment was specifically inhibited by peptides that contained the PP-epitope and by anti-NCAM univalent antibodies. The shortest active peptide has the sequence KYSFNYDGSE, suggesting that this site is directly involved in NCAM homophilic interaction.     

Anti-idiotype antibodies that mimic gp86 of human cytomegalovirus inhibit viral fusion but not attachment.

Human cytomegalovirus (CMV) infects cells by sequential processes involving attachment, fusion with the cell membrane, and penetration of the capsid. We used two monoclonal anti-idiotype that mimic one of the CMV envelope glycoproteins, gp86, to study its role in the early phases of CMV infection. Neither of two such antibodies inhibited virus binding to human embryonic lung (HEL) fibroblasts; however, both antibodies inhibited the fusion of CMV with HEL cells, as measured by an assay in which viral envelope is labeled with a fluorescent amphiphile (octadecyl rhodamine B chloride, or R18), resulting in increased fluorescence during fusion of virus with the cell membrane. Because these anti-idiotype antibodies were shown previously to bind to specific receptors on HEL cell membranes, these findings suggest that both gp86 and its cell membrane receptor may function in the fusion of human CMV with HEL cells.     

Hepatitis B virus (HBV) binding factor in human serum: candidate for a soluble form of hepatocyte HBV receptor.

A hepatitis B virus (HBV) binding factor (HBV-BF) was identified in normal human serum interacting with the pre-S1 and pre-S2 epitopes of the viral envelope located within the protein domains involved in recognition of hepatocyte receptor(s). This molecule was characterized as a 50-kDa glycoprotein showing an isoelectric point of 7.13 with a biological activity depending on its native molecular conformation and on intact sulfhydryl bonds. Monoclonal antibodies to HBV-BF recognized a membrane component of the normal human liver whereas they were unreactive with hepatocyte membranes of other species and with those of the HepG2 cell line. These results suggest that the HBV-BF represents a soluble fragment of the membrane component and can be related to the HBV receptor mediating attachment of HBV to human liver cells.     

Non-natural cell surface receptors: synthetic peptides capped with N-cholesterylglycine efficiently deliver proteins into Mammalian cells

Protein toxins such as shiga toxin and cholera toxin penetrate into cells by binding small molecule-based cell surface receptors localized to cholesterol and sphingolipid-rich lipid raft subdomains of cellular plasma membranes. Molecular recognition between these toxins and their receptors triggers endocytic protein uptake through endogenous membrane trafficking pathways. We report herein the synthesis of functionally related non-natural cell surface receptors comprising peptides capped with N-cholesterylglycine as the plasma membrane anchor. The peptide moieties of these receptors were based on high-affinity epitopes of anti-hemaglutinin antibodies (anti-HA), anti-Flag antibodies, and a moderate-affinity Strep Tag II peptide ligand of the streptavidin protein from Streptomyces avidini. These non-natural receptors were directly loaded into plasma membranes of Jurkat lymphocytes to display peptides from lipid rafts on the cell surface. Molecular recognition between these receptors and added cognate anti-HA, anti-Flag, or streptavidin proteins resulted in rapid clathrin-mediated endocytosis; fluorescent target proteins were completely internalized within 4-12 h of protein addition. Analysis of protein uptake by epifluorescence microscopy and flow cytometry revealed intracellular fluorescence enhancements of 100-fold to 200-fold (10 microM non-natural receptor) with typically >99% efficiency. This method enabled intracellular delivery of a functional Escherichia coli beta-galactosidase enzyme conjugated to Protein A from Staphylococcus aureus. We termed this novel delivery strategy "synthetic receptor targeting", which is an efficient method to enhance macromolecular uptake by decorating mammalian cells with chemically defined synthetic receptors that access the molecular machinery controlling the organization of cellular plasma membranes.     

N-terminal myristylation of HBV preS1 domain enhances receptor recognition.

The N-terminal portion of the large envelope protein of the human hepatitis B virus (HBV), the preS1 domain, plays a fundamental role in cell attachment and infectivity. Recent investigations have suggested that myristylation of preS1 Gly2 residue is essential for viral infectivity, but the importance of this post-translational modification on HBV-receptor interaction has not been elucidated completely. In this study we produced, using stepwise solid-phase chemical synthesis, the entire preS1[1-119] domain (adw2 subtype), and compared its receptor binding activity with the myristylated form, myristyl-preS1[2-119] in order to define the importance of fatty acid modification. Both synthetic proteins were fully characterized in terms of structural identity using TOF-MALDI mass spectrometry and analysis of tryptic fragments. Circular dichroism measurements indicated a low content of ordered structure in the preS1 protein, while the propensity of the myristylated derivative to assume a conformationally defined structure was more evident. HBV-receptor binding assays performed with plasma membranes preparations from the hepatocyte carcinoma cell line HepG2 clearly showed that the preS1[1-119] domain recognizes the HBV receptor, and confirmed that binding is occurring through the 21-47 region. The myristylated derivative recognized HBV receptor preparations with higher affinity than the preS1 domain, suggesting that the conformational transitions induced in the preS1 moiety by fatty acid post-translational modification are important for efficient attachment of viral particles to HBV receptors.     

General analysis of receptor-mediated viral attachment to cell surfaces.

Viruses are multivalent particles that attach to cells through one or more bonds between viral attachment proteins (VAP) and specific cellular receptors. Three modes of virus binding are presented that can explain the diversity in binding data observed among viruses. They are based on multivalency of attachment and spatial versus receptor saturation effects which are easily distinguished based upon simple criteria. Mode 1 involves only monovalent virus/receptor binding. Modes 2 and 3 involve multivalent bonds between the virus and cell; however, in mode 3 space on the cell surface becomes saturated before receptors. A model is developed for viral attachment that accounts for nonspecific binding, receptor/virus interactions, and spatial saturation effects. The model can describe each mode in different limits and can be applied to virus binding data to extract key physical information such as receptor number and affinity. These values are used to postulate the type of VAP/receptor interaction involved and to predict binding at different parameter values. For the mode 2 binding of Adenovirus 2, the model predicts a receptor number of 4-15 x 10(3) on HeLa cells and an affinity of 2-6 x 10(7) M-1 which closely approximate experimental estimates. For the binding of three, broad-host-range, enveloped viruses, Semliki Forest virus, Vesicular Stomatitis virus, and the baculovirus, Autographa californica nuclear polyhedrosis virus, the model predicts receptor numbers of 10(5) or greater and affinities in the range of 10(4) to 10(5) M-1. These values are indicative of a VAP/oligosaccharide interaction which has been documented for a number of other viruses. Experimental evidence is presented that is the first to demonstrate that baculovirus binding is mediated by a cell surface receptor.     

Peptide T from human immunodeficiency virus envelope does not interact with hepatic, intestinal and colonic vasoactive intestinal peptide (VIP) receptors

Acquired immunodeficiency syndrome (AIDS) is initiated by the attachment of the human immunodeficiency virus (HIV) to specific target cells. An octapeptide sequence contained within the envelope of HIV, peptide T, mediates the viral binding. Since there is a considerable structural homology between peptide T and VIP, it has been proposed that the VIP receptor may be the naturally occurring protein which provides the corresponding cellular attachment site. In three different models (rat intestinal epithelial cell membranes, rat liver plasma membranes and human colonic cells), we document the lack of interaction between peptide T and the VIP receptor. These observations would also exclude any pathophysiologic effect caused by the crossreactivity of peptide T or its analogues and these VIP receptors.