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Domain Organization of Lentiviral and Betaretroviral Surface Envelope Glycoproteins Modeled with AlphaFold. J Virol 2021; 96:e0134821. [PMID: 34705555 DOI: 10.1128/jvi.01348-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The surface envelope glycoproteins of non-primate lentiviruses and betaretroviruses share sequence similarity with the inner proximal domain β-sandwich of the human immunodeficiency virus type 1 (HIV-1) gp120 glycoprotein that faces the transmembrane glycoprotein as well as patterns of cysteine and glycosylation site distribution that points to a similar two-domain organization in at least some lentiviruses. Here, high reliability models of the surface glycoproteins obtained with the AlphaFold algorithm are presented for the gp135 glycoprotein of the small ruminant caprine arthritis-encephalitis (CAEV) and visna lentiviruses and the betaretroviruses jaagsiekte sheep retrovirus (JSRV), mouse mammary tumor virus (MMTV) and consensus human endogenous retrovirus type K (HERV-K). The models confirm and extend the inner domain structural conservation in these viruses and identify two outer domains with a putative receptor binding site in the CAEV and visna virus gp135. The location of that site is consistent with patterns of sequence conservation and glycosylation site distribution in gp135. In contrast, a single domain is modeled for the JSRV, MMTV and HERV-K betaretrovirus envelope proteins that is highly conserved structurally in the proximal region and structurally diverse in apical regions likely to interact with cell receptors. The models presented here identify sites in small ruminant lentivirus and betaretrovirus envelope glycoproteins likely to be critical for virus entry and virus neutralization by antibodies and will facilitate their functional and structural characterization. Importance Structural information on the surface envelope proteins of lentiviruses and related betaretroviruses is critical to understand mechanisms of virus-host interactions. However, experimental determination of these structures has been challenging and only the structure of the human immunodeficiency virus type 1 gp120 has been determined. The advent of the AlphaFold artificial intelligence method for structure prediction allows high-quality modeling of the structures of small ruminant lentiviral and betaretroviral surface envelope proteins. The models are consistent with much of previously described experimental data, show regions likely to interact with receptors and identify domains that may be involved in mechanisms of antibody neutralization resistance in the small ruminant lentiviruses. The models will allow more precise design of mutants to further determine mechanisms of viral entry and immune evasion in this group of viruses and constructs for structure of these surface envelope proteins.
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Furtado Araújo J, Andrioli A, Pinheiro RR, Sider LH, de Sousa ALM, de Azevedo DAA, Peixoto RM, Lima AMC, Damasceno EM, Souza SCR, Teixeira MFDS. Vertical transmissibility of small ruminant lentivirus. PLoS One 2020; 15:e0239916. [PMID: 33206648 PMCID: PMC7673514 DOI: 10.1371/journal.pone.0239916] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 09/15/2020] [Indexed: 12/18/2022] Open
Abstract
This study aimed to evaluate by means of Nested Polymerase Chain Reaction (nPCR), co-cultivation and sequencing, with genetic comparison between strains (mother/newborn), the occurrence of vertical transmission of Small Ruminant Lentiviruses (SRLV) from naturally occurring nannies infected for their offspring. For the detection of SRLV seropositive progenitors, blood was collected from 42 nannies in the final third of gestation in tubes with and without anticoagulant. The diagnostic tests used were Western Blot (WB) and nPCR. During the period of birth, the same blood collection procedure was performed on 73 newborns at zero hours of birth, with the same diagnostic tests. Seventeen blood samples from seven-day-old kids, proven positive for SRLV by nPCR, chosen at random, were subjected to coculture in goat synovial membrane (GSM) cells for 105 days. The pro-viral DNA extracted from the cell supernatant from the coculture was subjected to nPCR. For DNA sequencing from the nPCR products, nine positive samples were chosen at random, four nannies with their respective offspring, also positive. Each sample was performed in triplicate, thus generating 27 nPCR products of which only 19 were suitable for analysis. Among the 42 pregnant goats, in 50% (21/42) pro-viral DNA was detected by nPCR, while in the WB, only 7.14% (3/42) presented antibodies against SRLV. Regarding neonates, of the 73 kids, 34 (46.57%) were positive for the virus, using the nPCR technique, while in the serological test (WB), three positive animals (4.10%) were observed. The coculture of the 17 samples with a positive result in the nPCR was confirmed in viral isolation by amplification of the SRLV pro-viral DNA. When aligned, the pro-viral DNA sequences (nannies and their respective offspring) presented homology in relation to the standard strain CAEV Co. It was concluded that the transmission of SRLV through intrauterine route was potentially the source of infection in the newborn goats.
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Affiliation(s)
| | | | | | | | | | | | - Renato Mesquita Peixoto
- Embrapa Goats and Sheep, Sobral, Ceará, Brazil
- Scholarship for Regional Scientific Development of the National Council for Scientific and Technological Development (DCR-CNPq/FUNCAP), level C, Brasilia, Distrito Federal–DF, Brazil
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An Immunodominant Region of the Envelope Glycoprotein of Small Ruminant Lentiviruses May Function as Decoy Antigen. Viruses 2018; 10:v10050231. [PMID: 29724026 PMCID: PMC5977224 DOI: 10.3390/v10050231] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 04/28/2018] [Accepted: 04/30/2018] [Indexed: 02/04/2023] Open
Abstract
(1) Background: Small ruminant lentiviruses (SRLV) persist in infected goats that mount a strong humoral immune response characterized by low neutralizing titers. In this study, we characterized the antibody response to SU5, a variable, immunodominant epitope of the envelope glycoprotein of SRLV. We tested the working hypothesis that the variability of SU5 reflects escape from neutralizing antibody. (2) Methods: Affinity purified anti-SU5 antibody were tested for their neutralizing activity to the homologous lentivirus. Virus culture supernatant—in native form or following sonication and filtration—was used to test the ability of free envelope glycoproteins to compete for binding in a SU5-peptide-ELISA. (3) Results: Anti-SU5 antibodies are not neutralizing, strongly suggesting that they do not bind intact viral particles. In contrast, shed envelope glycoproteins efficiently compete for binding in a SU5-ELISA, providing convincing evidence that the SU5 epitope is exposed only on shed envelope glycoproteins. (4) Conclusions: Our results show that the antibody engaging SU5 is not neutralizing and does not appear to bind to SU expressed at the surface of virus particles. We propose that SU5 is a potential decoy epitope exposed on shaded envelope glycoproteins, luring the humoral immune response in committing an original antigenic sin to a functionally irrelevant epitope.
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Characterization of Ovine A3Z1 Restriction Properties against Small Ruminant Lentiviruses (SRLVs). Viruses 2017; 9:v9110345. [PMID: 29149056 PMCID: PMC5707552 DOI: 10.3390/v9110345] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 11/14/2017] [Accepted: 11/15/2017] [Indexed: 12/22/2022] Open
Abstract
Intrinsic factors of the innate immune system include the apolipoprotein B editing enzyme catalytic polypeptide-like 3 (APOBEC3) protein family. APOBEC3 inhibits replication of different virus families by cytosine deamination of viral DNA and a not fully characterized cytosine deamination-independent mechanism. Sheep are susceptible to small ruminant lentivirus (SRLVs) infection and contain three APOBEC3 genes encoding four proteins (A3Z1, Z2, Z3 and Z2-Z3) with yet not deeply described antiviral properties. Using sheep blood monocytes and in vitro-derived macrophages, we found that A3Z1 expression is associated with lower viral replication in this cellular type. A3Z1 transcripts may also contain spliced variants (A3Z1Tr) lacking the cytidine deaminase motif. A3Z1 exogenous expression in fully permissive fibroblast-like cells restricted SRLVs infection while A3Z1Tr allowed infection. A3Z1Tr was induced after SRLVs infection or stimulation of blood-derived macrophages with interferon gamma (IFN-γ). Interaction between truncated isoform and native A3Z1 protein was detected as well as incorporation of both proteins into virions. A3Z1 and A3Z1Tr interacted with SRLVs Vif, but this interaction was not associated with degradative properties. Similar A3Z1 truncated isoforms were also present in human and monkey cells suggesting a conserved alternative splicing regulation in primates. A3Z1-mediated retroviral restriction could be constrained by different means, including gene expression and specific alternative splicing regulation, leading to truncated protein isoforms lacking a cytidine-deaminase motif.
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Konishi M, Hayama Y, Shirafuji H, Kameyama KI, Murakami K, Tsutsui T, Akashi H. Serological survey of caprine arthritis-encephalitis virus infection in Japan. J Vet Med Sci 2015; 78:447-50. [PMID: 26498401 PMCID: PMC4829515 DOI: 10.1292/jvms.15-0357] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A serological survey of caprine arthritis-encephalitis virus (CAEV) infection was conducted from September 2006 to February 2007 in Japan. A total of 857 serum samples were collected from 113 herds in 28 prefectures and were analyzed for the presence of CAEV antibodies using agar gel immunodiffusion test. The seroprevalence of CAEV infection at the herd and animal levels was 15.0% (17/113) and 10.0% (86/857), respectively. Large farms with more than 10 goats and with animals for dairy and breeding purposes had higher seroprevalence (P<0.05). The results of this study provide useful information to consider effective control programs against CAEV infection in Japan.
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Affiliation(s)
- Misako Konishi
- National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan
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Bertolotti L, Mazzei M, Puggioni G, Carrozza ML, Dei Giudici S, Muz D, Juganaru M, Patta C, Tolari F, Rosati S. Characterization of new small ruminant lentivirus subtype B3 suggests animal trade within the Mediterranean Basin. J Gen Virol 2011; 92:1923-1929. [DOI: 10.1099/vir.0.032334-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Small ruminant lentiviruses (SRLVs) represent a group of viruses infecting sheep and goats worldwide. Despite the high heterogeneity of genotype A strains, which cluster into as many as ten subtypes, genotype B was believed to be less complex and has, so far, been subdivided into only two subtypes. Here, we describe two novel full-length proviral sequences isolated from Sarda sheep in two Italian regions. Genome sequence as well as the main linear epitopes clearly placed this cluster into genotype B. However, owing to long-standing segregation of this sheep breed, the genetic distances that are clearly >15 % with respect to B1 and B2 subtypes suggest the designation of a novel subtype, B3. Moreover the close relationship with a gag sequence obtained from a Turkish sheep adds new evidence to historical data that suggest an anthropochorous dissemination of hosts (small ruminants) and their pathogens (SRLV) during the colonization of the Mediterranean from the Middle East.
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Affiliation(s)
- L. Bertolotti
- Molecular Biotechnology Center, Università degli Studi di Torino, via Nizza 52, 10126 Torino, Italy
- Dipartimento di Produzioni Animali, Epidemiologia, Ecologia, Facoltà di Medicina Veterinaria, Università degli Studi di Torino, Via Leonardo da Vinci 44, 10095 Grugliasco (TO), Italy
| | - M. Mazzei
- Dipartimento di Patologia Animale, Profilassi ed Igiene degli Alimenti, Facoltà di Medicina Veterinaria, Università di Pisa, Viale delle Piagge 2, 56124 Pisa, Italy
| | - G. Puggioni
- Istituto Zooprofilattico Sperimentale della Sardegna, Sassari, Italy
| | - M. L. Carrozza
- Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
| | - S. Dei Giudici
- Istituto Zooprofilattico Sperimentale della Sardegna, Sassari, Italy
| | - D. Muz
- Faculty of Veterinary Medicine, Department of Virology, Mustafa Kemal University, Hatay, Turkey
| | - M. Juganaru
- Dipartimento di Produzioni Animali, Epidemiologia, Ecologia, Facoltà di Medicina Veterinaria, Università degli Studi di Torino, Via Leonardo da Vinci 44, 10095 Grugliasco (TO), Italy
| | - C. Patta
- Istituto Zooprofilattico Sperimentale della Sardegna, Sassari, Italy
| | - F. Tolari
- Dipartimento di Patologia Animale, Profilassi ed Igiene degli Alimenti, Facoltà di Medicina Veterinaria, Università di Pisa, Viale delle Piagge 2, 56124 Pisa, Italy
| | - S. Rosati
- Dipartimento di Produzioni Animali, Epidemiologia, Ecologia, Facoltà di Medicina Veterinaria, Università degli Studi di Torino, Via Leonardo da Vinci 44, 10095 Grugliasco (TO), Italy
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Juganaru M, Reina R, Bertolotti L, Stella M, Profiti M, Armentano M, Bollo E, Amorena B, Rosati S. In vitro properties of small ruminant lentivirus genotype E. Virology 2011; 410:88-95. [DOI: 10.1016/j.virol.2010.10.031] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 07/15/2010] [Accepted: 10/17/2010] [Indexed: 10/18/2022]
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Frequency of the serological reactivity against the caprine arthritis encephalitis lentivirus gp135 in children who consume goat milk. Arch Med Res 2009; 40:204-7. [PMID: 19427972 DOI: 10.1016/j.arcmed.2009.02.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Accepted: 01/09/2009] [Indexed: 11/23/2022]
Abstract
BACKGROUND Caprine arthritis encephalitis virus (CAEV) is a retrovirus belonging to the lentivirus genus that also includes the human immunodeficiency virus (HIV). CAEV may be transmitted to humans by goat milk consumption. It has been suggested that CAEV may also be involved in the immunological protection process against HIV, but this has not been demonstrated. Here we identified serological reactivity against CAEV gp135 in children who consumed goat milk. METHODS Thirty sera samples from children (males between 6 and 16 years of age) who regularly consumed goat milk and a negative control of 30 serum samples from children (males between 6 and 12 years) with no previous contact with goats or goat dairy products were used. All sera were tested by Western blot against CAEV antigens. RESULTS There were 18/30 serum samples from goat milk consumers that were reactive to CAEV gp135, and one reacted against gp50 simultaneously; none of the 30 serum samples from nonconsumers of goat dairy products reacted to viral proteins. CONCLUSIONS These results showed that the positive response to gp135 may be the result of a repetitive stimulation without viral replication or the result of CAEV replication in humans. CAEV gp135 is codified by the env gene located on the viral particle surface as well as gp50. Moreover, there are similarities between CAEV gp135 and HIV-1 gp120, so there is a possibility that CAEV replicates in humans and may participate in immunological cross-phenomena, but this should be further studied.
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Haflidadóttir BS, Matthíasdóttir S, Agnarsdóttir G, Torsteinsdóttir S, Pétursson G, Andrésson ÓS, Andrésdóttir V. Mutational analysis of a principal neutralization domain of visna/maedi virus envelope glycoprotein. J Gen Virol 2008; 89:716-721. [PMID: 18272763 DOI: 10.1099/vir.0.83410-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have shown previously that a type-specific neutralization domain is located within a 39 aa sequence in the fourth variable domain of gp135 in visna/maedi virus. We now show that neutralizing antibodies detected early in infection are directed to this epitope, suggesting an immunodominant nature of this domain. Ten antigenic variants were previously analysed for mutations in this region, and all but one were found to be mutated. To assess the importance of these mutations in replication and neutralization, we reconstructed several of the mutations in an infectious molecular clone and tested the resulting viruses for neutralization phenotype and replication. Mutation of a conserved cysteine was shown to alter the neutralization epitope, whilst the replication kinetics in macrophages were unchanged. Mutations modulating potential glycosylation sites were found in seven of the ten antigenic variants. A frequently occurring mutation, removing a potential glycosylation site, had no effect on its own on the neutralization phenotype of the virus. However, adding an extra potential glycosylation site in the region resulted in antigenic escape. The results indicate that the conserved cysteine plays a role in the structure of the epitope and that glycosylation may shield the principal neutralization site.
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Affiliation(s)
| | | | - Gudrún Agnarsdóttir
- Institute for Experimental Pathology, University of Iceland, Keldur, Reykjavík, Iceland
| | | | - Gudmundur Pétursson
- Institute for Experimental Pathology, University of Iceland, Keldur, Reykjavík, Iceland
| | - Ólafur S Andrésson
- Institute for Experimental Pathology, University of Iceland, Keldur, Reykjavík, Iceland
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Conservation of inner domain modules in the surface envelope glycoproteins of an ancient rabbit lentivirus and extant lentiviruses and betaretroviruses. Virology 2007; 372:201-7. [PMID: 18037464 DOI: 10.1016/j.virol.2007.10.038] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2007] [Revised: 10/15/2007] [Accepted: 10/31/2007] [Indexed: 11/23/2022]
Abstract
The consensus sequence of endogenous lentiviral elements in the genome of European rabbits (RELIK) was used to extend a model of conserved lentiviral and betaretroviral surface envelope glycoprotein (SU) inner domain structures. Here it is shown that nearly all the inner domain elements of human and simian immunodeficiency virus gp120 mediating conformational changes upon CD4 binding were conserved in the SU of RELIK. Many of these inner domain elements and a carboxy-terminal region outside the gp120 core are also conserved in the SU of other lentiviruses and betaretroviruses, suggesting conserved mechanisms of SU conformational changes induced by receptor binding.
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Immunogenicity of a polyvalent HIV-1 candidate vaccine based on fourteen wild type gp120 proteins in golden hamsters. BMC Immunol 2006; 7:25. [PMID: 17076905 PMCID: PMC1636068 DOI: 10.1186/1471-2172-7-25] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2006] [Accepted: 10/31/2006] [Indexed: 11/10/2022] Open
Abstract
Background One of the major obstacles in the design of an effective vaccine against HIV-1 is the hypervariability of the HIV-1 envelope glycoprotein. Most HIV-1 vaccine candidates have utilized envelope glycoprotein from a single virus isolate, but to date, none of them elicited broadly reactive humoral immunity. Herein, we hypothesised that a cocktail of HIV-1 gp120 proteins containing multiple epitopes may increase the breadth of immune responses against HIV-1. We compared and evaluated the immunogenicity of HIV-1 vaccines containing either gp120 protein alone or in combinations of four or fourteen gp120s from different primary HIV-1 isolates in immunized hamsters. Results We amplified and characterized 14 different gp120s from primary subtype B isolates with both syncytium and non-syncytium inducing properties, and expressed the proteins in Chinese Hamster Ovary (CHO) cell lines. Purified proteins were used either alone or in combinations of four or fourteen different gp120s to vaccinate golden hamsters. The polyvalent vaccine showed higher antibody titers to HIV-1 subtype B isolates MN and SF162 compared to the groups that received one or four gp120 proteins. However, the polyvalent vaccine was not able to show higher neutralizing antibody responses against HIV-1 primary isolates. Interestingly, the polyvalent vaccine group had the highest proliferative immune responses and showed a substantial proportion of cross-subtype CD4 reactivity to HIV-1 subtypes B, C, and A/E Conclusion Although the polyvalent approach achieved only a modest increase in the breadth of humoral and cellular immunity, the qualitative change in the vaccine (14 vs. 1 gp120) resulted in a quantitative improvement in vaccine-induced immunity.
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Gjerset B, Storset AK, Rimstad E. Genetic diversity of small-ruminant lentiviruses: characterization of Norwegian isolates of Caprine arthritis encephalitis virus. J Gen Virol 2006; 87:573-580. [PMID: 16476978 DOI: 10.1099/vir.0.81201-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Small-ruminant lentiviruses (SRLVs), including Caprine arthritis encephalitis virus (CAEV) in goats and maedi-visna virus (MVV) in sheep, are lentiviruses that, despite overall similarities, show considerable genetic variation in regions of the SRLV genome. To gain further knowledge about the genetic diversity and phylogenetic relationships among field isolates of SRLVs occurring in geographically distinct areas, the full-length genomic sequence of a CAEV isolate (CAEV-1GA) and partial env sequences obtained from Norwegian CAEV-infected goats were determined. The genome of CAEV-1GA consisted of 8919 bp. Alignment studies indicated significant diversity from published SRLV sequences. Deletions and hypervariability in the 5′ part of the env gene have implications for the size of the proposed CAEV-1GA Rev protein and the encoded surface glycoprotein (SU). The variable regions in the C-terminal part of SU obtained from Norwegian CAEV isolates demonstrate higher sequence divergence than has been described previously for SRLVs. Phylogenetic analysis based on SU sequences gives further support for a unique group designation. The results described here reveal a distant genetic relationship between Norwegian CAEV and other SRLVs and demonstrate that there is more geographical heterogeneity among SRLVs than reported previously.
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Affiliation(s)
- Britt Gjerset
- Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, Box 8146 Dep, N-0033 Oslo, Norway
| | - Anne K Storset
- Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, Box 8146 Dep, N-0033 Oslo, Norway
| | - Espen Rimstad
- Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, Box 8146 Dep, N-0033 Oslo, Norway
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Hötzel I, Cheevers WP. Mutations increasing exposure of a receptor binding site epitope in the soluble and oligomeric forms of the caprine arthritis-encephalitis lentivirus envelope glycoprotein. Virology 2005; 339:261-72. [PMID: 15992850 DOI: 10.1016/j.virol.2005.05.028] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Revised: 05/13/2005] [Accepted: 05/27/2005] [Indexed: 10/25/2022]
Abstract
The caprine arthritis-encephalitis (CAEV) and ovine maedi-visna (MVV) viruses are resistant to antibody neutralization, a feature shared with all other lentiviruses. Whether the CAEV gp135 receptor binding site(s) (RBS) in the functional surface envelope glycoprotein (Env) is protected from antibody binding, allowing the virus to resist neutralization, is not known. Two CAEV gp135 regions were identified by extrapolating a gp135 structural model that could affect binding of antibodies to the RBS: the V1 region and a short sequence analogous in position to the human immunodeficiency virus type 1 gp120 loop B postulated to be located between two major domains of CAEV gp135. Mutation of isoleucine-166 to alanine in the putative loop B of gp135 increased the affinity of soluble gp135 for the CAEV receptor(s) and goat monoclonal antibody (Mab) F7-299 which recognizes an epitope overlapping the gp135 RBS. The I166A mutation also stabilized or exposed the F7-299 epitope in anionic detergent buffers, indicating that the I166A mutation induces conformational changes and stabilizes the RBS of soluble gp135 and enhances Mab F7-299 binding. In contrast, the affinity of a V1 deletion mutant of gp135 for the receptor and Mab F7-299 and its structural stability did not differ from that of the wild-type gp135. However, both the I166A mutation and the V1 deletion of gp135 increased cell-to-cell fusion activity and binding of Mab F7-299 to the oligomeric Env. Therefore, the CAEV gp135 RBS is protected from antibody binding by mechanisms both dependent and independent of Env oligomerization which are disrupted by the V1 deletion and the I166A mutation, respectively. In addition, we found a correlation between side-chain beta-branching at amino acid position 166 and binding of Mab F7-299 to oligomeric Env and cell-to-cell fusion, suggesting local secondary structure constraints in the region around isoleucine-166 as one determinant of gp135 RBS exposure and antibody binding.
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Affiliation(s)
- Isidro Hötzel
- Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164-7040, USA.
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Trujillo JD, Kumpula-McWhirter NM, Hötzel KJ, Gonzalez M, Cheevers WP. Glycosylation of immunodominant linear epitopes in the carboxy-terminal region of the caprine arthritis-encephalitis virus surface envelope enhances vaccine-induced type-specific and cross-reactive neutralizing antibody responses. J Virol 2004; 78:9190-202. [PMID: 15308714 PMCID: PMC506968 DOI: 10.1128/jvi.78.17.9190-9202.2004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
This study evaluated type-specific and cross-reactive neutralizing antibodies induced by immunization with modified surface glycoproteins (SU) of the 63 isolate of caprine arthritis-encephalitis lentivirus (CAEV-63). Epitope mapping of sera from CAEV-infected goats localized immunodominant linear epitopes in the carboxy terminus of SU. Two modified SU (SU-M and SU-T) and wild-type CAEV-63 SU (SU-W) were produced in vaccinia virus and utilized to evaluate the effects of glycosylation or the deletion of immunodominant linear epitopes on neutralizing antibody responses induced by immunization. SU-M contained two N-linked glycosylation sites inserted into the target epitopes by R539S and E542N mutations. SU-T was truncated at 518A, upstream from the target epitopes, by introduction of termination codons at 519Y and 521Y. Six yearling Saanen goats were immunized subcutaneously with 30 microg of SU-W, SU-M, or SU-T in Quil A adjuvant and boosted at 3, 7, and 16 weeks. SU antibody titers determined by indirect enzyme-linked immunosorbent assay demonstrated anamnestic responses after each boost. Wild-type and modified SU-induced type-specific CAEV-63 neutralizing antibodies and cross-reactive neutralizing antibodies against CAEV-Co, a virus isolate closely related to CAEV-63, and CAEV-1g5, an isolate geographically distinct from CAEV-63, were determined. Immunization with SU-T resulted in altered recognition of SU linear epitopes and a 2.8- to 4.6-fold decrease in neutralizing antibody titers against CAEV-63, CAEV-Co, and CAEV-1g5 compared to titers of SU-W-immunized goats. In contrast, immunization with SU-M resulted in reduced recognition of glycosylated epitopes and a 2.4- to 2.7-fold increase in neutralizing antibody titers compared to titers of SU-W-immunized goats. Thus, the glycosylation of linear immunodominant nonneutralization epitopes, but not epitope deletion, is an effective strategy to enhance neutralizing antibody responses by immunization.
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Affiliation(s)
- J D Trujillo
- Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington 99164-7040, USA.
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