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.     

Mannose receptor targeting of tumor antigen pmel17 to human dendritic cells directs anti-melanoma T cell responses via multiple HLA molecules

Targeting recycling endocytic receptors with specific Abs provides a means for introducing a variety of tumor-associated Ags into human dendritic cells (DCs), culminating in their efficient presentation to T cells. We have generated a human mAb (B11) against the mannose receptor that is rapidly internalized by DCs through receptor-mediated endocytosis. By genetically linking the melanoma Ag, pmel17, to Ab B11, we obtained the fully human fusion protein, B11-pmel17. Treatment of DCs with B11-pmel17 resulted in the presentation of pmel17 in the context of HLA class I and class II molecules. Thus, potent pmel17-specific T cells were cytotoxic toward gp100(+) HLA-matched melanoma targets, but not HLA-mismatched melanoma or gp100(-) nonmelanoma tumor lines. Importantly, competitive inhibition of lysis of an otherwise susceptible melanoma cell line by cold targets pulsed with known gp100 CD8 T cell epitopes as well as a dose-dependent proliferative response to Th epitopes demonstrates that DCs can process targeted Ag for activation of cytotoxic as well as helper arms of the immune response. Thus, the specific targeting of soluble exogenous tumor Ag to the DC mannose receptor directly contributes to the generation of multiple HLA-restricted Ag-specific T cell responses.     

HIV-1 gp120 mannoses induce immunosuppressive responses from dendritic cells

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 is a vaccine immunogen that can signal via several cell surface receptors. To investigate whether receptor biology could influence immune responses to gp120, we studied its interaction with human, monocyte-derived dendritic cells (MDDCs) in vitro. Gp120 from the HIV-1 strain JR-FL induced IL-10 expression in MDDCs from 62% of donors, via a mannose C-type lectin receptor(s) (MCLR). Gp120 from the strain LAI was also an IL-10 inducer, but gp120 from the strain KNH1144 was not. The mannose-binding protein cyanovirin-N, the 2G12 mAb to a mannose-dependent gp120 epitope, and MCLR-specific mAbs inhibited IL-10 expression, as did enzymatic removal of gp120 mannose moieties, whereas inhibitors of signaling via CD4, CCR5, or CXCR4 were ineffective. Gp120-stimulated IL-10 production correlated with DC-SIGN expression on the cells, and involved the ERK signaling pathway. Gp120-treated MDDCs also responded poorly to maturation stimuli by up-regulating activation markers inefficiently and stimulating allogeneic T cell proliferation only weakly. These adverse reactions to gp120 were MCLR-dependent but independent of IL-10 production. Since such mechanisms might suppress immune responses to Env-containing vaccines, demannosylation may be a way to improve the immunogenicity of gp120 or gp140 proteins.     

The heat shock protein gp96: a receptor-targeted cross-priming carrier and activator of dendritic cells

Heat shock proteins like gp96 (grp94) are able to induce specific cytotoxic T-cell (CTL) responses against cells from which they originate and are currently studied in clinical trials for use in immunotherapy of tumors. We have recently demonstrated that gp96 binds to at least one yet unidentified receptor restricted to antigen-presenting cells (APCs) like dendritic cells (DCs) but not to T cells. Moreover we have shown, that for CTL activation by gp96-chaperoned peptides receptor-mediated uptake of gp96 by APCs is required. Lately, we have discovered a second function of gp96 when interacting with professional APCs. Gp96 is able to mediate maturation of DCs as determined by upregulation of MHC class II, CD86 and CD83 molecules, secretion of pro-inflammatory cytokines IL-12 and TNF-alpha and enhanced T-cell simulatory capacity. Furthermore, the gp96 receptor(s) are down-regulated on mature DCs, suggesting that the gp96 receptor(s) behave similar to other endocytic receptors like CD36, mannose receptor etc. Our findings now provide additional evidence for the remarkable immunogenicity of gp96: first, the existence of specific gp96 receptors on APCs and second, the capacity to activate dendritic cells which is strictly required to enable these highly sophisticated APCs to prime CTL responses.     

Mannose 6-Phosphate/Insulin-like growth factor II receptor mediates internalization and degradation of leukemia inhibitory factor but not signal transduction.

Leukemia inhibitory factor (LIF) is a multifunctional cytokine belonging to the interleukin-6 subfamily of helical cytokines, all of which use the glycoprotein (gp) 130 subunit for signal transduction. The specific receptor for LIF, gp190, binds this cytokine with low affinity and is also required for signal transduction. We have recently reported that glycosylated LIF produced by transfected Chinese hamster ovary cells also binds to a lectin-like receptor, mannose 6-phosphate/insulin-like growth factor II receptor (Man-6-P/IGFII-R) (Blanchard, F., Raher, S., Duplomb, L., Vusio, P., Pitard, V., Taupin, J. L., Moreau, J. F., Hoflack, B., Minvielle, S., Jacques, Y., and Godard, A. (1998) J. Biol. Chem. 273, 20886-20893). The present study shows that (i) mannose 6-phosphate-containing LIF is naturally produced by a number of normal and tumor cell lines; (ii) other cytokines in the interleukin-6 family do not bind to Man-6-P/IGFII-R; and (iii) another unrelated cytokine, macrophage-colony-stimulating factor, is also able to bind to Man-6-P/IGFII-R in a mannose 6-phosphate-sensitive manner. No functional effects or signal transductions mediated by this lectin-like receptor were observed in various biological assays after LIF binding, and mannose 6-phosphate-containing LIF was as active as non-glycosylated LIF. However, mannose 6-phosphate-sensitive LIF binding resulted in rapid internalization and degradation of the cytokine on numerous cell lines, which suggests that Man-6-P/IGFII-R plays an important role in regulating the amounts of LIF available in vivo.     

Structural and biosynthetic studies of the granule membrane protein, GMP-140, from human platelets and endothelial cells

GMP-140 is an integral membrane glycoprotein of apparent Mr = 140,000 located in secretory storage granules of platelets and vascular endothelial cells. When these cells are activated, GMP-140 redistributes from the membrane of the granules to the plasma membrane. To gain insight into the potential function of GMP-140, we examined aspects of its structure and biosynthesis. The amino acid composition of platelet GMP-140 revealed elevated numbers of cystinyl (6.1%), prolinyl (7.2%), and tryptophanyl (2.1%) residues. GMP-140 contained 28.8% carbohydrate by weight, distributed among N-acetylneuraminic acid, neutral sugar, and N-acetylglucosamine residues. Enzymatic removal of N-linked oligosaccarides reduced the protein's apparent Mr by more than 50,000. The biosynthesis of GMP-140 in HEL cells, which share biochemical features with megakaryocytes, was studied by pulse-chase labeling with [35S]cysteine followed by immunoprecipitation. HEL cells synthesized a heterogeneous GMP-140 precursor of 98-125 kDa which converted to a mature 140-kDa form within 40-60 min. Removal of high mannose oligosaccarides by endo-beta-N-acetylglucosaminidase H treatment reduced the apparent Mr of the precursor but not the mature protein. Tunicamycin-treated HEL cells synthesized three to four precursors of 80-92 kDa, suggesting the possibility of heterogeneity of GMP-140 at the protein level. Exposure of activated platelets to proteases followed by Western blotting indicated that most of the mass of GMP-140 was located on the extracytoplasmic side of the membrane. Our studies indicate that GMP-140 is a cysteine-rich, heavily glycosylated protein with a large extracytoplasmic domain. These features are compatible with a receptor function for the molecule when it is exposed on the surface of activated platelets and endothelial cells.     

Carbohydrates of human immunodeficiency virus. Structures of oligosaccharides linked to the envelope glycoprotein 120

Human T-cells (H9), persistently infected with the HTLV-III strain of human immunodeficiency virus, were metabolically labeled with D-[2-3H]mannose or D-[6-3H]glucosamine. The viral envelope glycoprotein, gp120, was isolated either from cell lysates or from cell-free culture supernatant. After proteolytic digestion, the radiolabeled oligosaccharides were sequentially liberated from glycopeptides by treatment with endo-beta-N-acetylhexosaminidase H and peptide:N-glycosidase F. Oligosaccharides released were separated from residual (glyco)peptides and fractionated according to size, charge, and fucose content. The individual oligosaccharide species obtained were characterized by digestion with exoglycosidases and by chromatographic comparison with standard oligosaccharides. Our results demonstrate that the intracellular gp120 carries predominantly oligomannosidic glycans comprising nine or eight mannose residues. The secreted glycoprotein is equally substituted by oligomannosidic species, containing seven to nine mannose residues, and by fucosylated, partially sialylated bi- and triantennary complex-type oligosaccharides.     

Effects of anti-gp120 monoclonal antibodies on CD4 receptor binding by the env protein of human immunodeficiency virus type 1.

Monoclonal antibodies (MAbs) to defined peptide epitopes on gp120 from human immunodeficiency virus type 1 were used to investigate the involvement of their epitopes in gp120 binding to the CD4 receptor. Recombinant vaccinia viruses were constructed that expressed either full-length gp120 (v-ED6), or a truncated gp120 lacking 44 amino acids at the carboxyl terminus (v-ED4). Binding of these glycoproteins to the CD4 receptor was detected directly with metabolically labeled gp120 or indirectly with the gp120 MAbs. Truncated gp120 from v-ED4 bound to CD4-positive cells less than 1/12 as well as gp120 from v-ED6, indicating that the C-terminal region of gp120, which is conserved in numerous isolates of human immunodeficiency virus type 1, is critical for CD4 binding. However, MAb 110-1, which recognizes a peptide contained in the region deleted from v-ED4 (amino acids 489 through 511), did not inhibit binding of gp120 to CD4. MAb 110-1 also reacted with gp120 bound to the CD4 receptor, indicating that the epitope for this antibody does not directly interact with CD4. A second MAb, 110-4, which recognizes a peptide epitope located between amino acids 303 and 323 and has potent viral neutralizing activity, also bound to gp120 on the CD4 receptor. Furthermore, pretreatment of gp120 with MAb 110-4 at concentrations approximately 1,000-fold higher than those required for complete virus neutralization inhibited subsequent CD4 binding by only about 65%. Taken together, these data suggest that neutralization mediated by antibody 110-4 does not result from binding of this MAb to the CD4-binding site of gp120.     

Natural killer cell-mediated cytotoxicity does not depend on recognition of mannose 6-phosphate residues

Interaction of mannose 6-phosphate-specific receptors with their ligands has been suggested to be essential for natural killer cell (NK)-mediated cytotoxicity. Indeed, mannose 6-phosphate-specific receptors and ligands bearing mannose 6-phosphate residues are demonstrable on human peripheral blood leukocytes with NK activity as well as on K-562 NK target cells, allowing at least in principle such an interaction. It can also be shown that NK activity of human peripheral blood leukocytes is inhibited by mannose 6-phosphate. The following observations, however, exclude an essential role of the mannose 6-phosphate receptor-ligand system in NK cell-mediated cytotoxicity. 1) NK cytotoxicity is sensitive to a broad range of structurally unrelated sugar phosphates. 2) NK activity is normal in patients with I cell disease (mucolipidosis II), which due to a genetic defect are unable to synthesize the ligands for the mannose 6-phosphate-specific receptor. 3) NK cytotoxicity is not inhibited by an antiserum against the mannose 6-phosphate receptor, which blocks the receptor function.     

Fine specificity of the human immune response to the major neutralization epitopes expressed on cytomegalovirus gp58/116 (gB), as determined with human monoclonal antibodies.

The humoral immune response to human cytomegalovirus (CMV) membrane glycoprotein gp58/116 (gB) has been studied by establishing cell lines producing specific human monoclonal antibodies. These cell lines were generated from peripheral blood lymphocytes obtained from a healthy carrier. Hybridomas producing gp58/116-specific antibodies were detected by reactivity to procaryotically expressed proteins containing the major neutralizing epitopes of this glycoprotein complex. One antibody, ITC88, which recognized an epitope located between amino acid residues 67 and 86 of gp116, potently neutralized the virus at 1 to 2 micrograms of immunoglobulin G per ml. Only four of the six human antibodies detecting the major neutralizing domain of gp58 neutralized the virus, and none of them required complement for activity. All antibodies that bound mature, processed gp58 recognized a conformational epitope involving sequences between residues 549 and 635. However, small differences existed between the antibodies in the actual minimal requirement for C- and N-terminal parts of this epitope. By peptide mapping with several of the antibodies, the epitope was shown to consist mainly of residues between amino acids 570 to 579 and 606 to 619. Despite the conformational nature of the epitope, the antibodies recognized both reduced and denatured native antigen. Presence of carbohydrates was not required for antigen binding of these gp58-specific human antibodies, but in at least one case, it greatly enhanced antigen recognition, indicating an importance of carbohydrate structures in some epitopes within the major neutralizing specificity of gp58.     

Purification of the human alveolar macrophage mannose receptor

We report here the first isolation of a mannose receptor from human lung, and identify the alveolar macrophage as the cell of origin. The receptor was purified from detergent-solubilized lung tissue by absorption to mannose- and fucose-Sepharose, and elution with EDTA. The eluted protein had a molecular weight of 175 kD. Maximum binding of 125I-mannan-2 to the isolated receptor occurred at pH 7.5. Binding was inhibited by 40 micrograms/ml mannan (75%); 200 mM mannose (89%); and 200 mM fucose (93%). Galactose (200 mM) had no effect. Polyclonal antibodies raised against the purified receptor reacted with the purified 175 kD protein and a 175 kD protein from detergent extracts of human alveolar macrophages by immunoblot analysis. The antibody immunoprecipitated a 175 kD protein from solubilized 125I-labeled human alveolar macrophage membranes. These studies indicate that the 175 kD protein purified from human lung is the cell surface alveolar macrophage mannose receptor.     

The dominant linear neutralizing antibody-binding site of glycoprotein gp86 of human cytomegalovirus is strain specific.

Bacterial fusion proteins, constructed from overlapping fragments of the open reading frame coding for gp86 of human cytomegalovirus (HCMV) strain AD169, were used to localize antigenic regions recognized by antibodies from human convalescent sera. A major domain for binding of conformation-independent antibodies was localized on fusion protein AP86, containing amino acids 15 to 142 of gp86. Human antibodies, affinity purified on AP86, neutralized infectious virus in tissue culture. In addition, a mouse monoclonal antibody (AP86-SA4), raised against AP86, also neutralized HCMV. AP86-SA4 was reactive with viral gp86 in immunoblot assays and showed a plasma membrane staining on intact HCMV-infected fibroblasts late in infection. After exonuclease III deletions of the viral gene, the binding site of neutralizing human as well as mouse antibodies was localized between amino acid residues 34 and 43. The domain has sequence variation between laboratory strains AD169 and Towne, and binding of the antibodies was strain specific. To our knowledge, this is the first characterization of a strain-specific neutralizing epitope on HCMV.     

Cytokine-enhanced expression of glycoprotein Ib alpha in human endothelium

Platelet glycoprotein Ib is a major platelet membrane protein composed of two disulfide-linked chains, termed the alpha and beta chains. The larger alpha chain (GpIb alpha), a platelet receptor for von Willebrand factor, plays a major role in mediating platelet adhesion to the subendothelium. Our laboratories have previously reported synthesis of a protein in human endothelial cells that is immunoprecipitated with polyclonal and monoclonal antibodies to platelet GpIb alpha. Lopez et al. (Lopez, J. A., Chung, D. W., Fujikawa, K., Hagan, F. S., Papayannopoulou, T., and Roth, G. J. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 5615-5619) have reported the cloning of GpIb alpha from a human erythroleukemia (HEL) cell cDNA library. Using this clone as probe, we have isolated two partial GpIb alpha clones from a human umbilical vein endothelial cell lambda gt11 cDNA library. These clones were localized within HEL-derived GpIb alpha cDNA by sequence and restriction enzyme analysis. Additionally, they detected the same message species in HEL and tonsilar RNA that was detected with the HEL GpIb alpha cDNA. Low level GpIb alpha mRNA expression was detected in cultured human umbilical vein endothelial cells, which was increased by treatment of the cells with tumor necrosis factor-alpha. This effect was enhanced by pretreatment with interferon-gamma. Additionally, localization of GpIb alpha in endothelium of fresh tonsilar tissue was demonstrated by immunohistochemistry and in situ hybridization. GpIb alpha may play a role in mediating platelet or other effector cell adhesion to activated endothelium.     

Growth control of hybridoma cells with an artificially induced EpoR-gp130 heterodimer

IL-6 has been known to modulate the growth of many hybridoma cells and also promote resultant antibody productivity. However, IL-6 is so expensive that the use of IL-6-dependent hybridomas for industrial antibody production is not practical. In this study, we aimed at designing antibody/gp130 and antibody/EpoR chimeras which could tightly control cell growth in response to more affordable cognate antigen. Retroviral vectors encoding V_H or V_L region of anti-hen egg lysozyme (HEL) antibody HyHEL-10 tethered to a pair of extracellular D2/transmembrane domains of erythropoietin receptor (EpoR) and cytoplasmic domains of either EpoR or gp130, were constructed, and a homodimeric or a heterodimeric pair of chimeric receptor combinations (V_H-gp130 and V_L-gp130 or V_H-gp130 and V_L-EpoR) were expressed in an IL-6-dependent hybridoma 7TD1. The chimeric receptor-derived growth signal was observed in both combinations, while some residual growth signal was observed in the absence of HEL. To reduce interchain interaction between the two receptor chains, we introduced mutations to the transmembrane domain of both chimera combinations. Consequently, the heterodimeric combination of V_H-gp130 and V_L-EpoR showed clear HEL-dependent cell growth, while the homodimeric combination of V_H-gp130 and V_L-gp130 showed reduced cell growth in the absence of HEL. This is the first report that an EpoR-gp130 cytoplasmic domain heterodimer could transduce a growth signal in hybridoma cells, indicating tight and economical growth control of hybridoma cells via our chimeric receptors.     

CD4-independent infection of astrocytes by human immunodeficiency virus type 1: requirement for the human mannose receptor

Human immunodeficiency virus type 1 (HIV-1) infection occurs in the central nervous system and causes a variety of neurobehavioral and neuropathological disorders. Both microglia, the residential macrophages in the brain, and astrocytes are susceptible to HIV-1 infection. Unlike microglia that express and utilize CD4 and chemokine coreceptors CCR5 and CCR3 for HIV-1 infection, astrocytes fail to express CD4. Astrocytes express several chemokine coreceptors; however, the involvement of these receptors in astrocyte HIV-1 infection appears to be insignificant. In the present study using an expression cloning strategy, the cDNA for the human mannose receptor (hMR) was found to be essential for CD4-independent HIV-1 infectivity. Ectopic expression of functional hMR rendered U87.MG astrocytic cells susceptible to HIV-1 infection, whereas anti-hMR serum and hMR-specific siRNA blocked HIV-1 infection in human primary astrocytes. In agreement with these findings, hMR bound to HIV-1 virions via the abundant and highly mannosylated sugar moieties of HIV-1 envelope glycoprotein gp120 in a Ca(2+)-dependent fashion. Moreover, hMR-mediated HIV-1 infection was dependent upon endocytic trafficking as assessed by transmission electron microscopy, as well as inhibition of viral entry by endosomo- and lysosomotropic drugs. Taken together, these results demonstrate the direct involvement of hMR in HIV-1 infection of astrocytes and suggest that HIV-1 interaction with hMR plays an important role in HIV-1 neuropathogenesis.     

The mannose-dependent epitope for neutralizing antibody 2G12 on human immunodeficiency virus type 1 glycoprotein gp120

We have analyzed the unique epitope for the broadly neutralizing human monoclonal antibody (MAb) 2G12 on the gp120 surface glycoprotein of human immunodeficiency virus type 1 (HIV-1). Sequence analysis, focusing on the conservation of relevant residues across multiple HIV-1 isolates, refined the epitope that was defined previously by substitutional mutagenesis (A. Trkola, M. Purtscher, T. Muster, C. Ballaun, A. Buchacher, N. Sullivan, K. Srinivasan, J. Sodroski, J. P. Moore, and H. Katinger, J. Virol. 70:1100-1108, 1996). In a biochemical study, we digested recombinant gp120 with various glycosidase enzymes of known specificities and showed that the 2G12 epitope is lost when gp120 is treated with mannosidases. Computational analyses were used to position the epitope in the context of the virion-associated envelope glycoprotein complex, to determine the variability of the surrounding surface, and to calculate the surface accessibility of possible glycan- and polypeptide-epitope components. Together, these analyses suggest that the 2G12 epitope is centered on the high-mannose and/or hybrid glycans of residues 295, 332, and 392, with peripheral glycans from 386 and 448 on either flank. The epitope is mannose dependent and composed primarily of carbohydrate, with probably no direct involvement of the gp120 polypeptide surface. It resides on a face orthogonal to the CD4 binding face, on a surface proximal to, but distinct from, that implicated in coreceptor binding. Its conservation amidst an otherwise highly variable gp120 surface suggests a functional role for the 2G12 binding site, perhaps related to the mannose-dependent attachment of HIV-1 to DC-SIGN or related lectins that facilitate virus entry into susceptible target cells.     

Structures of the carbohydrate chains of membrane glycoproteins IIb and IIIa of human platelets

Human platelet membrane glycoproteins IIb (GPIIb) and IIIa (GPIIIa), which have been proposed to be subunits of a receptor for fibrinogen, were purified from Triton X-100-solubilized platelet membranes by affinity chromatography on a concanavalin A (Con A)-Sepharose column followed by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Compositional analyses of the purified glycoproteins showed that GPIIb and GPIIIa contain 15% and 18% carbohydrate by weight, respectively, which consists of galactose, mannose, glucosamine, fucose, and sialic acid. This suggested that these glycoproteins contained N-linked carbohydrate chains. The carbohydrate chains were released from each glycoprotein by hydrazinolysis and then fractionated by ion-exchange chromatography on a Mono Q column. From each glycoprotein, mono-, di-, and trisialylated and neutral oligosaccharide fractions were obtained. The structures of these oligosaccharides were investigated by means of compositional and methylation analyses and digestion by exoglycosidase, and their reactivities to immobilized lectins were also examined. The neutral oligosaccharides, which comprised about 14% of the total oligosaccharides released from GPIIb and about 52% of that from GPIIIa, were found to be of the high mannose-type, in that they contained 5 or 6 mannose residues. On the other hand, a major part of the acidic oligosaccharides was found to consist of typical bi- and triantennary complex-type sugar chains, and much smaller amounts of tetraantennary complex-type sugar chains, and complex-type sugar chains with a fucosyl residue at a N-acetylglucosamine residue in the peripheral portion or a bisecting N-acetylglucosamine at a beta-mannosyl residue in the core portion were also detected. In conclusion, we found that GPIIb contained mainly complex-type sugar chains, whereas high mannose-type sugar chains were the predominant carbohydrate units in GPIIIa, and that the detected differences in the carbohydrate moieties of GPIIb and GPIIIa were quantitative but not qualitative.     

人星形细胞HIV—1膜蛋白gp120新受体的免疫学鉴定

自1994年首次报导HIV－1外膜蛋白gp120与人胎儿星形细胞膜蛋白质位点（推测分子量为260kD,命名为PAG）结合以来[1],这项工作持续集中于研究该蛋白的功能与作用,本研究藉助杂交瘤技术建立了一系列不鼠抗人星形细胞PAG）的单克隆抗体,这些抗体成功的抑制了gp120与PAG的结合,抑制可达50％以上,并几乎完全阻断了gp120介导的由摄入所星表细胞风钙离子的升高,通过ELISA可证实抗体与星形细胞的特异反应,蛋白印迹和免疫沉淀试验结果表明PAG作为实体的存在,试验表明PAG对于gp120与星形细胞的结合,对于gp120个导的星形细胞摄入所致钙离子的升高均有决定性作用,许多方向报导和研究表明gp120可与多种细胞结合而导致HIV－1感染,由此推论PAG是HIV－1gp120在人星形细胞上的新受体,同时也可能对HIV－1脑病的治疗开辟一条崭新的途径,PAG是否为HIV－1感染人星形细胞的受体,仍有等进一步实验证明。     

Processing of the gp55-116 envelope glycoprotein complex (gB) of human cytomegalovirus.

The processing pathway of the major envelope glycoprotein complex, gp55-116 (gB), of human cytomegalovirus was studied using inhibitors of glycosylation and endoglycosidases. The results of these studies indicated that the mature gp55-116 is synthesized by the addition of both simple and complex N-linked sugars to a nonglycosylated precursor of estimated Mr 105,000. In a rapid processing step, the Mr 105,000 precursor is glycosylated to a protein of Mr 150,000 (gp150) which contains only endoglycosidase H-sensitive sugar linkages. The gp150 is then processed relatively slowly to a Mr 165,000 to 170,000 species (gp165-170), which is then cleaved to yield the mature gp55-116. Monensin prevented the final processing steps of the gp150, including cleavage, suggesting that transport through the Golgi apparatus is required for complete processing. Digestion of the intracellular forms of this complex as well as the virion forms confirmed the above findings and indicated that the mature virion form of gp55 contains 8,000 daltons of N-linked sugars. The virion gp116 contains some 52,000 to 57,000 daltons of N-linked carbohydrates and approximately 5,000 daltons of O-linked sugars.     

Functional mimicry of a human immunodeficiency virus type 1 coreceptor by a neutralizing monoclonal antibody

Interaction of the human immunodeficiency virus type 1 (HIV-1) gp120 envelope glycoprotein with the primary receptor, CD4, promotes binding to a chemokine receptor, either CCR5 or CXCR4. The chemokine receptor-binding site on gp120 elicits CD4-induced (CD4i) antibodies in some HIV-1-infected individuals. Like CCR5 itself, the CD4i antibody 412d exhibits a preference for CCR5-using HIV-1 strains and utilizes sulfated tyrosines to achieve binding to gp120. Here, we show that 412d binding requires the gp120 beta19 strand and the base of the V3 loop, elements that are important for the binding of the CCR5 N terminus. Two gp120 residues in the V3 loop base determined 412d preference for CCR5-using HIV-1 strains. A chimeric molecule in which the 412d heavy-chain third complementarity-determining loop sequence replaces the CCR5 N terminus functioned as an efficient second receptor, selectively supporting the entry of CCR5-using HIV-1 strains. Sulfation of N-terminal tyrosines contributed to the function of this chimeric receptor. These results emphasize the close mimicry of the CCR5 N terminus by the gp120-interactive region of a naturally elicited CD4i antibody.