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Liang S, Ratnayake PU, Keinath C, Jia L, Wolfe R, Ranaweera A, Weliky DP. Efficient Fusion at Neutral pH by Human Immunodeficiency Virus gp41 Trimers Containing the Fusion Peptide and Transmembrane Domains. Biochemistry 2018; 57:1219-1235. [PMID: 29345922 DOI: 10.1021/acs.biochem.7b00753] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Human immunodeficiency virus (HIV) is membrane-enveloped, and an initial infection step is joining/fusion of viral and cell membranes. This step is catalyzed by gp41, which is a single-pass integral viral membrane protein. The protein contains an ∼170-residue ectodomain located outside the virus that is important for fusion and includes the fusion peptide (FP), N-helix, loop, C-helix, and viral membrane-proximal external region (MPER). The virion initially has noncovalent complexes between three gp41 ectodomains and three gp120 proteins. A gp120 contains ∼500 residues and functions to identify target T-cells and macrophages via binding to specific protein receptors of the target cell membrane. gp120 moves away from the gp41 ectodomain, and the ectodomain is thought to bind to the target cell membrane and mediate membrane fusion. The secondary and tertiary structures of the ectodomain are different in the initial complex with gp120 and the final state without gp120. There is not yet imaging of gp41 during fusion, so the temporal relationship between the gp41 and membrane structures is not known. This study describes biophysical and functional characterization of large gp41 constructs that include the ectodomain and transmembrane domain (TM). Significant fusion is observed of both neutral and anionic vesicles at neutral pH, which reflects the expected conditions of HIV/cell fusion. Fusion is enhanced by the FP, which in HIV/cell fusion likely contacts the host membrane, and the MPER and TM, which respectively interfacially contact and traverse the HIV membrane. Initial contact with vesicles is made by protein trimers that are in a native oligomeric state that reflects the initial complex with gp120 and also is commonly observed for the ectodomain without gp120. Circular dichroism data support helical structure for the N-helix, C-helix, and MPER and nonhelical structure for the FP and loop. Distributions of monomer, trimer, and hexamer states are observed by size-exclusion chromatography (SEC), with dependences on solubilizing detergent and construct. These SEC and other data are integrated into a refined working model of HIV/cell fusion that includes dissociation of the ectodomain into gp41 monomers followed by folding into hairpins that appose the two membranes, and subsequent fusion catalysis by trimers and hexamers of hairpins. The monomer and oligomer gp41 states may therefore satisfy dual requirements for HIV entry of membrane apposition and fusion.
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Affiliation(s)
- S Liang
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - P U Ratnayake
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - C Keinath
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - L Jia
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - R Wolfe
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - A Ranaweera
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
| | - D P Weliky
- Department of Chemistry, Michigan State University , East Lansing, Michigan 48824, United States
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Serrano S, Huarte N, Rujas E, Andreu D, Nieva JL, Jiménez MA. Structure-Related Roles for the Conservation of the HIV-1 Fusion Peptide Sequence Revealed by Nuclear Magnetic Resonance. Biochemistry 2017; 56:5503-5511. [PMID: 28930470 DOI: 10.1021/acs.biochem.7b00745] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Despite extensive characterization of the human immunodeficiency virus type 1 (HIV-1) hydrophobic fusion peptide (FP), the structure-function relationships underlying its extraordinary degree of conservation remain poorly understood. Specifically, the fact that the tandem repeat of the FLGFLG tripeptide is absolutely conserved suggests that high hydrophobicity may not suffice to unleash FP function. Here, we have compared the nuclear magnetic resonance (NMR) structures adopted in nonpolar media by two FP surrogates, wtFP-tag and scrFP-tag, which had equal hydrophobicity but contained wild-type and scrambled core sequences LFLGFLG and FGLLGFL, respectively. In addition, these peptides were tagged at their C-termini with an epitope sequence that folded independently, thereby allowing Western blot detection without interfering with FP structure. We observed similar α-helical FP conformations for both specimens dissolved in the low-polarity medium 25% (v/v) 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), but important differences in contact with micelles of the membrane mimetic dodecylphosphocholine (DPC). Thus, whereas wtFP-tag preserved a helix displaying a Gly-rich ridge, the scrambled sequence lost in great part the helical structure upon being solubilized in DPC. Western blot analyses further revealed the capacity of wtFP-tag to assemble trimers in membranes, whereas membrane oligomers were not observed in the case of the scrFP-tag sequence. We conclude that, beyond hydrophobicity, preserving sequence order is an important feature for defining the secondary structures and oligomeric states adopted by the HIV FP in membranes.
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Affiliation(s)
- Soraya Serrano
- Institute of Physical Chemistry "Rocasolano" (IQFR-CSIC) , Serrano 119, E-28006 Madrid, Spain
| | - Nerea Huarte
- Biofisika Institute (CSIC-UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country , P.O. Box 644, 48080 Bilbao, Spain
| | - Edurne Rujas
- Biofisika Institute (CSIC-UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country , P.O. Box 644, 48080 Bilbao, Spain
| | - David Andreu
- Proteomics and Protein Chemistry Unit, Department of Experimental and Health Sciences, Pompeu Fabra University , Barcelona Biomedical Research Park, Dr. Aiguader 88, 08003 Barcelona, Spain
| | - José L Nieva
- Biofisika Institute (CSIC-UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country , P.O. Box 644, 48080 Bilbao, Spain
| | - María Angeles Jiménez
- Institute of Physical Chemistry "Rocasolano" (IQFR-CSIC) , Serrano 119, E-28006 Madrid, Spain
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Shai Y. ATR-FTIR studies in pore forming and membrane induced fusion peptides. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012. [PMID: 23201348 DOI: 10.1016/j.bbamem.2012.11.027] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Infrared (IR) spectroscopy has been shown to be very reliable for the characterization, identification and quantification of structural data. Particularly, the Attenuated Total Reflectance (ATR) technique which became one of the best choices to study the structure and organization of membrane proteins and membrane-bound peptides in biologically relevant membranes. An important advantage of IR spectroscopy is its ability to analyze material under a very wide range of conditions including solids, liquids and gases. This method allows elucidation of component secondary structure elements of a peptide or protein in a global manner, and by using site specific isotope labeling allows determination of specific regions. A few advantages in using ATR-FTIR spectroscopy include; a relatively simple technique, allow the determination of peptide orientation in the membrane, allow the determination of secondary structures of very small peptides, and importantly, the method is sensitive to isotopic labeling on the scale of single amino acids. Many studies were reported on the use of ATR-FTIR spectroscopy in order to study the structure and orientation of membrane bound hydrophobic peptides and proteins. The list includes native and de-novo designed peptides, as well as those derived from trans-membrane domains of various receptors (TMDs). The present review will focus on several examples that demonstrate the potential and the simplicity in using the ATR-FTIR approach to determine secondary structures of proteins and peptides when bound, inserted, and oligomerized within membranes. The list includes (i) a channel forming protein/peptide: the Ca(2+) channel phospholamban, (ii) a cell penetrating peptide, (iii) changes in the structure of a transmembrane domain located within ordered and non-ordered domains, and (iv) isotope edited FTIR to directly assign structure to the membrane associated fusion peptide in context of a Key gp41 Structural Motif. Importantly, a unique advantage of infrared spectroscopy is that it allows a simultaneous study of the structure of lipids and proteins in intact biological membranes without an introduction of foreign perturbing probes. Because of the long IR wavelength, light scattering problems are virtually non-existent. This allows the investigation of highly aggregated materials or large membrane fragments. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies.
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Affiliation(s)
- Yechiel Shai
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel.
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Garg H, Viard M, Jacobs A, Blumenthal R. Targeting HIV-1 gp41-induced fusion and pathogenesis for anti-viral therapy. Curr Top Med Chem 2012; 11:2947-58. [PMID: 22044225 DOI: 10.2174/156802611798808479] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Revised: 02/28/2011] [Accepted: 12/01/2011] [Indexed: 11/22/2022]
Abstract
HIV gp41 is a metastable protein whose native conformation is maintained in the form of a heterodimer with gp120. The non-covalently associated gp41/gp120 complex forms a trimer on the virus surface. As gp120 engages with HIV's receptor, CD4, and coreceptor, CXCR4 or CCR5, gp41 undergoes several conformational changes resulting in fusion between the viral and cellular membranes. Several lipophilic and amphiphilic domains have been shown to be critical in that process. While the obvious function of gp41 in viral entry is well-established its role in cellular membrane fusion and the link with pathogenesis are only now beginning to appear. Recent targeting of gp41 via fusion inhibitors has revealed an important role of this protein not only in viral entry but also in bystander apoptosis and HIV pathogenesis. Studies by our group and others have shown that the phenomenon of gp41-mediated hemifusion initiates apoptosis in bystander cells and correlates with virus pathogenesis. More interestingly, recent clinical evidence suggests that gp41 mutants arising after Enfuvirtide therapy are associated with CD4 cell increase and immunological benefits. This has in turn been correlated to a decrease in bystander apoptosis in our in vitro as well as in vivo assays. Although a great deal of work has been done to unravel HIV-1 gp41-mediated fusion mechanisms, the factors that regulate gp41-mediated fusion versus hemifusion and the mechanism by which hemifusion initiates bystander apoptosis are not fully understood. Further insight into these issues will open new avenues for drug development making gp41 a critical anti-HIV target both for neutralization and virus attenuation.
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Affiliation(s)
- Himanshu Garg
- Center of Excellence for Infectious Disease, Department of Biomedical Sciences, Texas Tech University Health Sciences Center, El Paso, TX 79905, USA
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Hartmann L, Neveling K, Borkens S, Schneider H, Freund M, Grassman E, Theiss S, Wawer A, Burdach S, Auerbach AD, Schindler D, Hanenberg H, Schaal H. Correct mRNA processing at a mutant TT splice donor in FANCC ameliorates the clinical phenotype in patients and is enhanced by delivery of suppressor U1 snRNAs. Am J Hum Genet 2010; 87:480-93. [PMID: 20869034 DOI: 10.1016/j.ajhg.2010.08.016] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Revised: 08/26/2010] [Accepted: 08/31/2010] [Indexed: 12/19/2022] Open
Abstract
The U1 small nuclear RNA (U1 snRNA) as a component of the major U2-dependent spliceosome recognizes 5' splice sites (5'ss) containing GT as the canonical dinucleotide in the intronic positions +1 and +2. The c.165+1G>T germline mutation in the 5'ss of exon 2 of the Fanconi anemia C (FANCC) gene commonly predicted to prevent correct splicing was identified in nine FA patients from three pedigrees. RT-PCR analysis of the endogenous FANCC mRNA splicing pattern of patient-derived fibroblasts revealed aberrant mRNA processing, but surprisingly also correct splicing at the TT dinucleotide, albeit with lower efficiency. This consequently resulted in low levels of correctly spliced transcript and minute levels of normal posttranslationally processed FANCD2 protein, indicating that this naturally occurring TT splicing might contribute to the milder clinical manifestations of the disease in these patients. Functional analysis of this FANCC 5'ss within splicing reporters revealed that both the noncanonical TT dinucleotide and the genomic context of FANCC were required for the residual correct splicing at this mutant 5'ss. Finally, use of lentiviral vectors as a delivery system to introduce expression cassettes for TT-adapted U1 snRNAs into primary FANCC patient fibroblasts allowed the correction of the DNA-damage-induced G2 cell-cycle arrest in these cells, thus representing an alternative transcript-targeting approach for genetic therapy of inherited splice-site mutations.
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Affiliation(s)
- Linda Hartmann
- Institute of Virology, Heinrich-Heine-University, D-40225 Düsseldorf, Germany
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Cheng SF, Chien MP, Lin CH, Chang CC, Lin CH, Liu YT, Chang DK. The fusion peptide domain is the primary membrane-inserted region and enhances membrane interaction of the ectodomain of HIV-1 gp41. Mol Membr Biol 2010; 27:31-44. [PMID: 19995328 DOI: 10.3109/09687680903333847] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
To execute the membrane fusion function, it is necessary for the fusion protein of the virus to penetrate into the hydrophobic milieu of membrane bilayer. Hence identification of the region(s) of the ectodomain of viral fusion proteins involved in the membrane insertion and their interaction with the rest of the fusion protein in the membrane would be important for the mechanistic study of membrane fusion. To this end, we examined membrane activity of the fusion peptide, and the ectodomain protein with or without the fusion peptide domain of HIV-1 gp41 by several biophysical measurements. The results revealed that the ectodomain protein containing the fusion peptide domain had higher membrane-perturbing activity and deeper membrane insertion, while the construct lacking the fusion peptide domain had much lower membrane activity. Strikingly, the N-terminal heptad repeat region was found to be induced deeper into the membrane by the fusion peptide, consistent with the role of the latter in the membrane penetration. We concluded that the fusion peptide is the only stretch of gp41 ectodomain that embeds deeply in the membrane interior in the prefusion stage. The function of fusion peptide in terms of membrane interaction and the implications of its interplay with other domains of gp41 on the membrane fusion cascade were discussed.
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Affiliation(s)
- Shu-Fang Cheng
- Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China
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Pan J, Lai CB, Scott WRP, Straus SK. Synthetic Fusion Peptides of Tick-Borne Encephalitis Virus as Models for Membrane Fusion. Biochemistry 2009; 49:287-96. [DOI: 10.1021/bi9017895] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jinhe Pan
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
| | - C. Benjamin Lai
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
| | - Walter R. P. Scott
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
| | - Suzana K. Straus
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
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Pang W, Tam SC, Zheng YT. Current peptide HIV type-1 fusion inhibitors. Antivir Chem Chemother 2009; 20:1-18. [PMID: 19794228 DOI: 10.3851/imp1369] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
There are now 26 antiretroviral drugs and 6 fixed-dose combinations, including reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors and fusion (or entry) inhibitors, approved by the US Food and Drug Administration for clinical use. Although they are clinically effective when used in combination, none of the existing drugs are considered ideal because of toxic side effects and the ascendance of inducing drug-resistant mutants. Development of new antiviral agents is essential. In the past decades, there has been great progress in understanding the structure of HIV type-1 (HIV-1) gp41 and the mechanism of HIV-1 entry into host cells. This opened up a promising avenue for rationally designed agents to interfere with this process. A number of fusion inhibitors have been developed to block HIV-1 replication. Enfuvirtide (T20) was one of those approved for clinical use. This signalled a new era in AIDS therapeutics. It is a synthetic polypeptide with potent inhibitory activity against HIV-1 infection. However, it is sensitive to proteolytic digestion and resistant virus strains are easily induced with multiple clinical use. One of the directions in designing new fusion inhibitors is to overcome these shortages. In the past years, large numbers of promising fusion inhibitory peptides have emerged. The antiviral activities are more potent or they can act differently from that of T20. Some of these new compounds have great potential to be further developed as therapeutic agents. This article reviewed some recent developments of these peptides and the possible role in anti-HIV-1 therapy.
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Affiliation(s)
- Wei Pang
- Key Laboratory of Animal Models and Human Diseases Mechanisms, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan, China
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Tu Y, Kim JS. A fusogenic segment of glycoprotein H from herpes simplex virus enhances transfection efficiency of cationic liposomes. J Gene Med 2008; 10:646-54. [PMID: 18383507 DOI: 10.1002/jgm.1184] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
BACKGROUND Low cellular uptake and endosomal escape are regarded as major limitations for nonviral gene delivery. In the present study, we use cationic liposomes incorporating fusogenic peptides from glycoprotein H of herpes simplex virus to improve cellular internalization and endosomal release of cationic liposome-DNA complexes. METHODS A synthetic analogue of a fusogenic peptide domain in glycoprotein H from herpes simplex virus was evaluated for in vitro gene delivery. The fusogenicity of the peptide was evaluated by a lipid mixing assay in neutral and acidic environments. The influence of the peptide on cellular internalization and subcellular distribution of Lipofectamine-pGL3 complexes were evaluated by flow cytometry, fluorescence microscopy, and confocal laser scanning microscopy. The effect of the peptide on transfection efficiency of cationic liposomes was also evaluated by luciferase assay in human cell lines. RESULTS A pH-sensitive fusogenicity of the wild-type peptide was observed. In the lipid mixing assay, the peptide mediated 80% membrane fusion at pH 7.4 at a 0.05 : 1 (peptide : lipid) mole ratio. At pH 4.5, 100% of membrane fusion was observed at a 0.005 : 1 ratio. Adding the peptide to Lipofectamine-pGL3 complexes significantly increased cellular uptake and, thus, increased transgene expression up to 30-fold in human cell lines. Nuclear localization of the DNA complex by the fusogenic peptide was observed by confocal microscopy. CONCLUSIONS A synthetic analogue of a fusogenic peptide domain from herpes simplex virus has been proven to improve cationic lipid-mediated transfection in vitro. The application of this fusogenic peptide will lead to improved strategies for transfection and successful gene therapy.
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Affiliation(s)
- Ying Tu
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN 38163, USA
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The membrane-proximal external region of the human immunodeficiency virus type 1 envelope: dominant site of antibody neutralization and target for vaccine design. Microbiol Mol Biol Rev 2008; 72:54-84, table of contents. [PMID: 18322034 DOI: 10.1128/mmbr.00020-07] [Citation(s) in RCA: 202] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Enormous efforts have been made to produce a protective vaccine against human immunodeficiency virus type 1; there has been little success. However, the identification of broadly neutralizing antibodies against epitopes on the highly conserved membrane-proximal external region (MPER) of the gp41 envelope protein has delineated this region as an attractive vaccine target. Furthermore, emerging structural information on the MPER has provided vaccine designers with new insights for building relevant immunogens. This review describes the current state of the field regarding (i) the structure and function of the gp41 MPER; (ii) the structure and binding mechanisms of the broadly neutralizing antibodies 2F5, 4E10, and Z13; and (iii) the development of an MPER-targeting vaccine. In addition, emerging approaches to vaccine design are presented.
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Qiang W, Bodner ML, Weliky DP. Solid-state NMR spectroscopy of human immunodeficiency virus fusion peptides associated with host-cell-like membranes: 2D correlation spectra and distance measurements support a fully extended conformation and models for specific antiparallel strand registries. J Am Chem Soc 2008; 130:5459-71. [PMID: 18370385 DOI: 10.1021/ja077302m] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The human immunodeficiency virus (HIV) is "enveloped" by a membrane, and infection of a host cell begins with fusion between viral and target cell membranes. Fusion is catalyzed by the HIV gp41 protein which contains a functionally critical approximately 20-residue apolar "fusion peptide" (HFP) that associates with target cell membranes. In this study, chemically synthesized HFPs were associated with host-cell-like membranes and had "scatter-uniform" labeling (SUL), that is, only one residue of each amino acid type was U-(13)C, (15)N labeled. For the first sixteen HFP residues, an unambiguous (13)C chemical shift assignment was derived from 2D (13)C/(13)C correlation spectra with short mixing times, and the shifts were consistent with continuous beta-strand conformation. (13)C-(13)C contacts between residues on adjacent strands were derived from correlation spectra with long mixing times and suggested close proximity of the following residues: Ala-6/Gly-10, Ala-6/Phe-11, and Ile-4/Gly-13. Specific antiparallel beta-strand registries were further tested using a set of HFPs that were (13)CO-labeled at Ala-14 and (15)N-labeled at either Val-2, Gly-3, Ile-4, or Gly-5. The solid-state NMR data were fit with 50-60% population of antiparallel HFP with either Ala-14/Gly-3 or Ala-14/Ile-4 registries and 40-50% population of structures not specified by the NMR experiments. The first two registries correlated with intermolecular hydrogen bonding of 15-16 apolar N-terminal residues and this hydrogen-bonding pattern would be consistent with a predominant location of these residues in the hydrophobic membrane interior. To our knowledge, these results provide the first residue-specific structural models for membrane-associated HFP in its beta-strand conformation.
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Affiliation(s)
- Wei Qiang
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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Asang C, Hauber I, Schaal H. Insights into the selective activation of alternatively used splice acceptors by the human immunodeficiency virus type-1 bidirectional splicing enhancer. Nucleic Acids Res 2008; 36:1450-63. [PMID: 18203748 PMCID: PMC2275126 DOI: 10.1093/nar/gkm1147] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The guanosine-adenosine-rich exonic splicing enhancer (GAR ESE) identified in exon 5 of the human immunodeficiency virus type-1 (HIV-1) pre-mRNA activates either an enhancer-dependent 5′ splice site (ss) or 3′ ss in 1-intron reporter constructs in the presence of the SR proteins SF2/ASF2 and SRp40. Characterizing the mode of action of the GAR ESE inside the internal HIV-1 exon 5 we found that this enhancer fulfils a dual splicing regulatory function (i) by synergistically mediating exon recognition through its individual SR protein-binding sites and (ii) by conferring 3′ ss selectivity within the 3′ ss cluster preceding exon 5. Both functions depend upon the GAR ESE, U1 snRNP binding at the downstream 5′ ss D4 and the E42 sequence located between these elements. Therefore, a network of cross-exon interactions appears to regulate splicing of the alternative exons 4a and 5. As the GAR ESE-mediated activation of the upstream 3′ ss cluster also is essential for the processing of intron-containing vpu/env-mRNAs during intermediate viral gene expression, the GAR enhancer substantially contributes to the regulation of viral replication.
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Affiliation(s)
- Corinna Asang
- Institut für Virologie, Universitätsklinikum Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany
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13
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Fatty acids can substitute the HIV fusion peptide in lipid merging and fusion: an analogy between viral and palmitoylated eukaryotic fusion proteins. J Mol Biol 2007; 374:220-30. [PMID: 17919659 DOI: 10.1016/j.jmb.2007.09.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2007] [Revised: 08/20/2007] [Accepted: 09/04/2007] [Indexed: 11/22/2022]
Abstract
Various fusion proteins from eukaryotes and viruses share structural similarities such as a coiled coil motif. However, compared with eukaryotic proteins, a viral fusion protein contains a fusion peptide (FP), which is an N-terminal hydrophobic fragment that is primarily involved in directing fusion via anchoring the protein to the target cell membrane. In various eukaryotic fusion proteins the membrane targeting domain is cysteine-rich and must undergo palmitoylation prior to the fusion process. Here we examined whether fatty acids can replace the FP of human immunodeficiency virus type 1 (HIV-1), thereby discerning between the contributions of the sequence versus hydrophobicity of the FP in the lipid-merging process. For that purpose, we structurally and functionally characterized peptides derived from the N terminus of HIV fusion protein - gp41 in which the FP is lacking or replaced by fatty acids. We found that fatty acid conjugation dramatically enhanced the capability of the peptides to induce lipid mixing and aggregation of zwitterionic phospholipids composing the outer leaflet of eukaryotic cell membranes. The enhanced effect of the acylated peptides on membranes was further supported by real-time atomic force microscopy (AFM) showing nanoscale holes in zwitterionic membranes. Membrane-binding experiments revealed that fatty acid conjugation did not increase the affinity of the peptides to the membrane significantly. Furthermore, all free and acylated peptides exhibited similar alpha-helical structures in solution and in zwitterionic membranes. Interestingly, the fusogenic active conformation of N36 in negatively charged membranes composing the inner leaflet of eukaryotic cells is beta-sheet. Apparently, N-terminal heptad repeat (NHR) can change its conformation as a response to a change in the charge of the membrane head group. Overall, the data suggest an analogy between the eukaryotic cysteine-rich domains and the viral fusion peptide, and mark the hydrophobic nature of FP as an important characteristic for its role in lipid merging.
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14
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Gabrys CM, Weliky DP. Chemical shift assignment and structural plasticity of a HIV fusion peptide derivative in dodecylphosphocholine micelles. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:3225-34. [PMID: 17935693 DOI: 10.1016/j.bbamem.2007.07.028] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Revised: 07/31/2007] [Accepted: 07/31/2007] [Indexed: 10/22/2022]
Abstract
A "HFPK3" peptide containing the 23 residues of the human immunodeficiency virus (HIV) fusion peptide (HFP) plus three non-native C-terminal lysines was studied in dodecylphosphocholine (DPC) micelles with 2D 1H NMR spectroscopy. The HFP is at the N-terminus of the gp41 fusion protein and plays an important role in fusing viral and target cell membranes which is a critical step in viral infection. Unlike HFP, HFPK3 is monomeric in detergent-free buffered aqueous solution which may be a useful property for functional and structural studies. H alpha chemical shifts indicated that DPC-associated HFPK3 was predominantly helical from I4 to L12. In addition to the highest-intensity crosspeaks used for the first chemical shift assignment (denoted I), there were additional crosspeaks whose intensities were approximately 10% of those used for assignment I. A second assignment (II) for residues G5 to L12 as well as a few other residues was derived from these lower-intensity crosspeaks. Relative to the I shifts, the II shifts were different by 0.01-0.23 ppm with the largest differences observed for HN. Comparison of the shifts of DPC-associated HFPK3 with those of detergent-associated HFP and HFP derivatives provided information about peptide structures and locations in micelles.
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Affiliation(s)
- Charles M Gabrys
- Department of Chemistry, Michigan State University, East Lansing, MI 48824-1320, USA
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15
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Qiang W, Yang J, Weliky DP. Solid-state nuclear magnetic resonance measurements of HIV fusion peptide to lipid distances reveal the intimate contact of beta strand peptide with membranes and the proximity of the Ala-14-Gly-16 region with lipid headgroups. Biochemistry 2007; 46:4997-5008. [PMID: 17417873 PMCID: PMC2631438 DOI: 10.1021/bi6024808] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Human immunodeficiency virus (HIV) infection begins with fusion between viral and host cell membranes and is catalyzed by the HIV gp41 fusion protein. The approximately 20 N-terminal apolar residues of gp41 are called the HIV fusion peptide (HFP), interact with the host cell membrane, and play a key role in fusion. In this study, the membrane location of peptides which contained the HFP sequence (AVGIGALFLGFLGAAGSTMGARS) was probed in samples containing either only phospholipids or phospholipids and cholesterol. Four HFPs were examined which each contained 13CO labeling at three sequential residues between G5 and G16. The 13CO chemical shifts indicated that HFP had predominant beta strand conformation over the labeled residues in the samples. The internuclear distances between the HFP 13CO groups and the lipid 31P atoms were measured using solid-state nuclear magnetic resonance rotational-echo double-resonance experiments. The shortest 13CO-31P distances of 5-6 A were observed for HFP labeled between A14 and G16 and correlated with intimate association of beta strand HFP and membranes. These results were confirmed with measurements using HFPs singly labeled with 13CO at A6 or A14. To our knowledge, these data are the first measurements of distances between HIV fusion peptide nuclei and lipid P, and qualitative models of the membrane location of oligomeric beta strand HFP which are consistent with the experimental data are presented. Observation of intimate contact between beta strand HFP and membranes provides a rationale for further investigation of the relationship between structure and fusion activity for this conformation.
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Affiliation(s)
- Wei Qiang
- Department of Chemistry, Michigan State University, East Lansing, MI 48824
| | - Jun Yang
- Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195
| | - David P. Weliky
- Department of Chemistry, Michigan State University, East Lansing, MI 48824
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16
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Kammler S, Otte M, Hauber I, Kjems J, Hauber J, Schaal H. The strength of the HIV-1 3' splice sites affects Rev function. Retrovirology 2006; 3:89. [PMID: 17144911 PMCID: PMC1697824 DOI: 10.1186/1742-4690-3-89] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Accepted: 12/04/2006] [Indexed: 11/16/2022] Open
Abstract
Background The HIV-1 Rev protein is a key component in the early to late switch in HIV-1 splicing from early intronless (e.g. tat, rev) to late intron-containing Rev-dependent (e.g. gag, vif, env) transcripts. Previous results suggested that cis-acting sequences and inefficient 5' and 3' splice sites are a prerequisite for Rev function. However, we and other groups have shown that two of the HIV-1 5' splice sites, D1 and D4, are efficiently used in vitro and in vivo. Here, we focus on the efficiency of the HIV-1 3' splice sites taking into consideration to what extent their intrinsic efficiencies are modulated by their downstream cis-acting exonic sequences. Furthermore, we delineate their role in RNA stabilization and Rev function. Results In the presence of an efficient upstream 5' splice site the integrity of the 3' splice site is not essential for Rev function whereas an efficient 3' splice site impairs Rev function. The detrimental effect of a strong 3' splice site on the amount of Rev-dependent intron-containing HIV-1 glycoprotein coding (env) mRNA is not compensatable by weakening the strength of the upstream 5' splice site. Swapping the HIV-1 3' splice sites in an RRE-containing minigene, we found a 3' splice site usage which was variably dependent on the presence of the usual downstream exonic sequence. The most evident activation of 3' splice site usage by its usual downstream exonic sequence was observed for 3' splice site A1 which was turned from an intrinsic very weak 3' splice site into the most active 3' splice site, even abolishing Rev activity. Performing pull-down experiments with nuclear extracts of HeLa cells we identified a novel ASF/SF2-dependent exonic splicing enhancer (ESE) within HIV-1 exon 2 consisting of a heptameric sequence motif occurring twice (M1 and M2) within this short non-coding leader exon. Single point mutation of M1 within an infectious molecular clone is detrimental for HIV-1 exon 2 recognition without affecting Rev-dependent vif expression. Conclusion Under the conditions of our assay, the rate limiting step of retroviral splicing, competing with Rev function, seems to be exclusively determined by the functional strength of the 3' splice site. The bipartite ASF/SF2-dependent ESE within HIV-1 exon 2 supports cross-talk between splice site pairs across exon 2 (exon definition) which is incompatible with processing of the intron-containing vif mRNA. We propose that Rev mediates a switch from exon to intron definition necessary for the expression of all intron-containing mRNAs.
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Affiliation(s)
- Susanne Kammler
- Institut für Virologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 22.21, D-40225 Düsseldorf, Germany
- Department of Molecular Biology, University of Aarhus, C.F. Møllers Allé, Bldg. 1130, DK-8000 Aarhus C, Denmark
| | - Marianne Otte
- Institut für Virologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 22.21, D-40225 Düsseldorf, Germany
- Institut für Genetik, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 26.03, D-40225 Düsseldorf, Germany
| | - Ilona Hauber
- Heinrich-Pette-Institute for Experimental Virology and Immunology, Martinistrasse 52, D-20251 Hamburg, Germany
| | - Jørgen Kjems
- Department of Molecular Biology, University of Aarhus, C.F. Møllers Allé, Bldg. 1130, DK-8000 Aarhus C, Denmark
| | - Joachim Hauber
- Heinrich-Pette-Institute for Experimental Virology and Immunology, Martinistrasse 52, D-20251 Hamburg, Germany
| | - Heiner Schaal
- Institut für Virologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Geb. 22.21, D-40225 Düsseldorf, Germany
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17
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Hager-Braun C, Katinger H, Tomer KB. The HIV-neutralizing monoclonal antibody 4E10 recognizes N-terminal sequences on the native antigen. THE JOURNAL OF IMMUNOLOGY 2006; 176:7471-81. [PMID: 16751393 DOI: 10.4049/jimmunol.176.12.7471] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Characterization of the epitope recognized by the broadly neutralizing anti-HIV Ab 4E10 has, heretofore, focused on a linear sequence from the gp41 pretransmembrane region (PTMR). Attempts to generate neutralizing Abs based on this linear epitope sequence have been unsuccessful. We have characterized the antigenic determinants on recombinant glycosylated full-length Ags, and nonglycosylated and truncated Ags recognized by 4E10 using epitope extraction and excision assays in conjunction with MALDI mass spectrometry. The mAb recognized the peptides (34)LWVTVYYGVPVWK(46) and (512)AVGIGAVFLGFLGAAGSTMGAASMTLTVQAR(542) located at the N-terminal region of gp120 and gp41, respectively. Immunoassays verified AV(L/M)FLGFLGAA as the gp41 epitope core. Recognition of the peptide from the gp41 PTMR was detected only in constructs in which the N termini of the mature envelope proteins were missing. In this region, the epitope core is located in the sequence (672)WFDITNWLWY(681). We hypothesize that the hydrophobic surface of the paratope functions as a "trap" for the viral sequences, which are responsible for insertion into the host cell membrane. As the N-terminal region of gp120, the fusogenic peptide of gp41, and the PTMR of gp41 show high sequence homology among various HIV strains, this model is consistent with the broadly neutralizing capabilities of 4E10.
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Affiliation(s)
- Christine Hager-Braun
- National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA.
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18
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Sackett K, Wexler-Cohen Y, Shai Y. Characterization of the HIV N-terminal fusion peptide-containing region in context of key gp41 fusion conformations. J Biol Chem 2006; 281:21755-21762. [PMID: 16751188 DOI: 10.1074/jbc.m603135200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Central to our understanding of human immunodeficiency virus-induced fusion is the high resolution structure of fragments of the gp41 fusion protein folded in a low energy core conformation. However, regions fundamental to fusion, like the fusion peptide (FP), have yet to be characterized in the context of the cognate protein regardless of its conformation. Based on conformation-specific monoclonal antibody recognition, we identified the polar region consecutive to the N36 fragment as a stabilizer of trimeric coiled-coil assembly, thereby enhancing inhibitory potency. This tertiary organization is retained in the context of the hydrophobic FP (N70 fragment). Our data indicate that the N70 fragment recapitulates the expected organization of this region in the viral fusion intermediate (N-terminal half of the pre-hairpin intermediate (N-PHI)), which happens to be the prime target for fusion inhibitors. Regarding the low energy conformation, we show for the first time core formation in the context of the FP (N70 core). The alpha-helical and coiled-coil stabilizing polar region confers substantial thermal stability to the core, whereas the hydrophobic FP does not add further stability. For the two key fusion conformations, N-PHI and N70 core, we find that the FP adopts a nonhelical structure and directs higher order assembly (assembly of coiled coils in N-PHI and assembly of bundles in the N70 core). This supra-molecular organization of coiled coils or folded cores is seen only in the context of the FP. This study is the first to characterize the FP region in the context of the folded core and provides a basic understanding of the role of the elusive FP for key gp41 fusion conformations.
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Affiliation(s)
- Kelly Sackett
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yael Wexler-Cohen
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yechiel Shai
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
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19
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Charloteaux B, Lorin A, Crowet JM, Stroobant V, Lins L, Thomas A, Brasseur R. The N-terminal 12 Residue Long Peptide of HIV gp41 is the Minimal Peptide Sufficient to Induce Significant T-cell-like Membrane Destabilization in Vitro. J Mol Biol 2006; 359:597-609. [PMID: 16677669 DOI: 10.1016/j.jmb.2006.04.018] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2006] [Accepted: 04/03/2006] [Indexed: 11/26/2022]
Abstract
Here, we predicted the minimal N-terminal fragment of gp41 required to induce significant membrane destabilization using IMPALA. This algorithm is dedicated to predict peptide interaction with a membrane. We based our prediction of the minimal fusion peptide on the tilted peptide theory. This theory proposes that some protein fragments having a peculiar distribution of hydrophobicity adopt a tilted orientation at a hydrophobic/hydrophilic interface. As a result of this orientation, tilted peptides should disrupt the interface. We analysed in silico the membrane-interacting properties of gp41 N-terminal peptides of different length derived from the isolate BRU and from an alignment of 710 HIV strains available on the Los Alamos National Laboratory. Molecular modelling results indicated that the 12 residue long peptide should be the minimal fusion peptide. We then assayed lipid-mixing and leakage of T-cell-like liposomes with N-terminal peptides of different length as first challenge of our predictions. Experimental results confirmed that the 12 residue long peptide is necessary and sufficient to induce membrane destabilization to the same extent as the 23 residue long fusion peptide. In silico analysis of some fusion-incompetent mutants presented in the literature further revealed that they cannot insert into a modelled membrane correctly tilted. According to this work, the tilted peptide model appears to explain at least partly the membrane destabilization properties of HIV fusion peptide.
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Affiliation(s)
- B Charloteaux
- Centre de Biophysique Moléculaire Numérique, Faculté Universitaire des Sciences Agronomiques, Passage des déportés, B-5030 Gembloux, Belgium.
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20
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Gómara MJ, Lorizate M, Huarte N, Mingarro I, Perez-Payá E, Nieva JL. Hexapeptides that interfere with HIV-1 fusion peptide activity in liposomes block GP41-mediated membrane fusion. FEBS Lett 2006; 580:2561-6. [PMID: 16647705 DOI: 10.1016/j.febslet.2006.04.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2005] [Revised: 03/24/2006] [Accepted: 04/03/2006] [Indexed: 10/24/2022]
Abstract
Upon receptor-mediated activation, the gp41 hydrophobic, conserved fusion peptide inserts into the target membrane and promotes the kind of perturbations required for the progression of the HIV-cell fusion reaction. Using a synthetic combinatorial library we have identified all d-amino acid hexapeptide sequences that inhibited the fusion peptide capacity of perturbing model membranes. Two hexapeptides that effectively inhibited the fusion peptide in these systems were subsequently shown to inhibit cell-cell fusion promoted by gp41 expressed at cell surfaces. These observations might be of importance for understanding the mechanisms underlying fusion peptide activity and suggest new strategies for screening compounds that target these viral sequences.
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Affiliation(s)
- María J Gómara
- Biofisika Unitatea, CSIC-UPV/EHU, and Biokimika Saila, Euskal Herriko Unibertsitatea, Posta Kutxa 644, 48080 Bilbao, Spain
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21
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Heise T, Sommer G, Reumann K, Meyer I, Will H, Schaal H. The hepatitis B virus PRE contains a splicing regulatory element. Nucleic Acids Res 2006; 34:353-63. [PMID: 16410615 PMCID: PMC1331995 DOI: 10.1093/nar/gkj440] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Revised: 12/12/2005] [Accepted: 12/23/2005] [Indexed: 12/12/2022] Open
Abstract
The posttranscriptional regulatory element (PRE) is considered to enhance hepatitis B virus (HBV) gene expression by facilitating the nuclear export of intronless viral subgenomic RNAs. Its role in the RNA metabolism of the viral pregenomic RNA (pgRNA) is currently unknown. We identified a positively cis-acting splicing regulatory element (SRE-1) and present two lines of evidence for its functionality. Firstly, in a heterologous context SRE-1 functionally substitutes for a retroviral bidirectional exonic splicing enhancer (ESE). As expected, SRE-1 is a splicing enhancer also in its natural viral sequence context, since deletion of SRE-1 reduces splicing of pgRNA in cell culture experiments. Secondly, we show that stimulation of HBV RNA splicing by the splicing factor PSF was repressed by the PRE. Analysis of a variety of PSF mutants indicated that RNA-binding and protein-protein interaction were required to enhance splicing. In addition, we show that the PRE contributed to pgRNA stability, but has little influence on its nuclear export. Herein, we report for the first time that the PRE harbors splicing stimulating and inhibiting regulatory elements controlling processing of the viral pregenome. We discuss a model in which the regulation of pgRNA splicing depends on cellular factors interacting with the PRE.
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Affiliation(s)
- Tilman Heise
- Heinrich-Pette-Institut für Experimentelle Virologie und Immunologie an der Universität Hamburg, Martinistrasse 52, D-20251 Hamburg, Germany.
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22
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Freund M, Hicks MJ, Konermann C, Otte M, Hertel KJ, Schaal H. Extended base pair complementarity between U1 snRNA and the 5' splice site does not inhibit splicing in higher eukaryotes, but rather increases 5' splice site recognition. Nucleic Acids Res 2005; 33:5112-9. [PMID: 16155183 PMCID: PMC1201333 DOI: 10.1093/nar/gki824] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Spliceosome formation is initiated by the recognition of the 5′ splice site through formation of an RNA duplex between the 5′ splice site and U1 snRNA. We have previously shown that RNA duplex formation between U1 snRNA and the 5′ splice site can protect pre-mRNAs from degradation prior to splicing. This initial RNA duplex must be disrupted to expose the 5′ splice site sequence for base pairing with U6 snRNA and to form the active spliceosome. Here, we investigated whether hyperstabilization of the U1 snRNA/5′ splice site duplex interferes with splicing efficiency in human cell lines or nuclear extracts. Unlike observations in Saccharomyces cerevisiae, we demonstrate that an extended U1 snRNA/5′ splice site interaction does not decrease splicing efficiency, but rather increases 5′ splice site recognition and exon inclusion. However, low complementarity of the 5′ splice site to U1 snRNA significantly increases exon skipping and RNA degradation. Although the splicing mechanisms are conserved between human and S.cerevisiae, these results demonstrate that distinct differences exist in the activation of the spliceosome.
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Affiliation(s)
| | - Martin J. Hicks
- Department of Microbiology and Molecular Genetics, School of Medicine, University of CaliforniaIrvine, Irvine, CA 92697, USA
| | | | | | - Klemens J. Hertel
- Department of Microbiology and Molecular Genetics, School of Medicine, University of CaliforniaIrvine, Irvine, CA 92697, USA
| | - Heiner Schaal
- To whom correspondence should be addressed. Tel: +49 211 81 12393; Fax: +49 211 81 12227;
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23
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Castano S, Desbat B. Structure and orientation study of fusion peptide FP23 of gp41 from HIV-1 alone or inserted into various lipid membrane models (mono-, bi- and multibi-layers) by FT-IR spectroscopies and Brewster angle microscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1715:81-95. [PMID: 16126160 DOI: 10.1016/j.bbamem.2005.07.008] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2005] [Revised: 07/12/2005] [Accepted: 07/19/2005] [Indexed: 11/18/2022]
Abstract
In the present work, we study the structure and the orientation of the 23 N-terminal peptide of the HIV-1 gp 41 protein (AVGIGALFLGFLGAAGSTMGARS) called FP23. The behaviour of FP23 was investigated alone at the air/water interface and inserted into various lipid model systems: in monolayer or multibilayers of a DOPC/cholesterol/DOPE/DOPG (6/5/3/2) and in a DMPC bilayer. PMIRRAS and polarized ATR spectroscopy coupled with Brewster angle microscopy and spectral simulations were used to precisely determine the structure and the orientation of the peptide in its environment as well as the lipid perturbations induced by the FP23 insertion. The infra-red results show the structural polymorphism of the FP23 and its ability to transit quasi irreversibly from an alpha-helix to antiparallel beta-sheets. At the air/water interface, the transition is induced by compression of the peptide alone and is modulated by compression and lipid to peptide ratio (Ri) when FP23 is inserted into a lipid monolayer. In multibilayers and in a single bilayer, there is coexistence in quasi equal proportions of alpha-helix and antiparallel beta-sheets of FP23 at low peptide content (Ri=100, 200) while antiparallel beta-sheets are predominant at high FP23 concentration (Ri=50). In (multi)bilayer systems, evaluation of dichroic ratios and sprectral simulations show that both the alpha-helix and the antiparallel beta-sheets are tilted at diluted FP23 concentrations (tilt angle of alpha-helix with respect to the normal of the interface=36.5+/-3.0 degrees for FP23 in multibilayers of DOPC/Chol/DOPE/DOPG at Ri=200 and 39.0+/-5.0 degrees in a single bilayer of DMPC at Ri=100 and tilt angle of the beta-sheets=36.0+/-2.0 degrees for the beta-sheets in multibilayers and 30.0+/-2.0 degrees in the lipid bilayer). In parallel, the FP23 induces an increase of the lipid chain disorder which shows both by an increase of the methylene stretching frequencies and an increase of the average C-C-C angle of the acyl chains. At high FP23 content (Ri=50), the antiparallel beta-sheets induce a complete disorganization of the lipid chains in (multi)bilayers.
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Affiliation(s)
- Sabine Castano
- Laboratoire de Physico-Chimie Moléculaire, UMR CNRS 5803, Université de Bordeaux I, 351 cours de la Libération, 33405 Talence, France.
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24
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Gong R, Peng X, Kang S, Feng H, Huang J, Zhang W, Lin D, Tien P, Xiao G. Structural characterization of the fusion core in syncytin, envelope protein of human endogenous retrovirus family W. Biochem Biophys Res Commun 2005; 331:1193-200. [PMID: 15883002 PMCID: PMC7092852 DOI: 10.1016/j.bbrc.2005.04.032] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Indexed: 02/01/2023]
Abstract
Syncytin is a captive retroviral envelope protein, possibly involved in the formation of the placental syncytiotrophoblast layer generated by trophoblast cell fusion at the maternal–fetal interface. We found that syncytin and type I viral envelope proteins shared similar structural profiling, especially in the regions of N- and C-terminal heptad repeats (NHR and CHR). We expressed the predicted regions of NHR (41 aa) and CHR (34 aa) in syncytin as a native single chain (named 2-helix protein) to characterize it. 2-helix protein exists as a trimer and is highly α-helix, thermo-stable, and denatured by low pH. NHR and CHR could form a protease-resistant complex. The complex structure built by the molecular docking demonstrated that NHR and CHR associated in an antiparallel manner. Overall, the 2-helix protein could form a thermo-stable coiled coil trimer. The fusion core structure of syncytin was first demonstrated in endogenous retrovirus. These results support the explanation how syncytin mediates cytotrophoblast cell fusion involved in placental morphogenesis.
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Affiliation(s)
- Rui Gong
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Xiaoxue Peng
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Shuli Kang
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Huixing Feng
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Jianying Huang
- Shanghai Institute of Meteria Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 201203, China
| | - Wentao Zhang
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
| | - Donghai Lin
- Shanghai Institute of Meteria Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 201203, China
| | - Po Tien
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
- Corresponding authors. Fax: +86 27 68752897
| | - Gengfu Xiao
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
- Corresponding authors. Fax: +86 27 68752897
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25
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Sackett K, Shai Y. The HIV Fusion Peptide Adopts Intermolecular Parallel β-Sheet Structure in Membranes when Stabilized by the Adjacent N-Terminal Heptad Repeat: A 13C FTIR Study. J Mol Biol 2005; 350:790-805. [PMID: 15964015 DOI: 10.1016/j.jmb.2005.05.030] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2005] [Revised: 05/16/2005] [Accepted: 05/17/2005] [Indexed: 10/25/2022]
Abstract
The HIV gp41 protein mediates fusion with target host cells. The region primarily involved in directing fusion, the fusion peptide (FP), is poorly understood at the level of structure and function due to its toxic effect in expression systems. To overcome this, we used a synthetic approach to generate the N70 construct, whereby the FP is stabilized in context of the adjacent auto oligomerization domain. The amide I profile of unlabeled N70 in membranes reveals prominent alpha-helical contribution, along with significant beta-structure. By truncating the N terminus (FP region) of N70, beta-structure is eliminated, suggesting that the FP adopts a beta-structure in membranes. To assess this directly, (13)C Fourier-transformed infra-red analysis was carried out to map secondary structure of the 16 N-terminal hydrophobic residues of the fusion peptide (FP16). The (13)C isotope shifted absorbance of the FP was filtered from the global secondary structure of the 70 residue construct (N70). On the basis of the peak shift induced by the (13)C-labeled residues of FP16, we directly assign beta-sheet structure in ordered membranes. A differential labeling scheme in FP16 allows us to distinguish the type of beta-sheet structure as parallel. Dilution of each FP16-labeled N70 peptide, by mixing with unlabeled N70, shows directly that the FP16 beta-strand region self-assembles. We discuss our structural findings in the context of the prevailing gp41 fusion paradigm. Specifically, we address the role of the FP region in organizing supramolecular gp41 assembly, and we also discuss the mechanism by which exogenous, free FP constructs inhibit gp41-induced fusion.
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Affiliation(s)
- Kelly Sackett
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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26
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Yang J, Prorok M, Castellino FJ, Weliky DP. Oligomeric beta-structure of the membrane-bound HIV-1 fusion peptide formed from soluble monomers. Biophys J 2004; 87:1951-63. [PMID: 15345571 PMCID: PMC1304598 DOI: 10.1529/biophysj.103.028530] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2003] [Accepted: 06/01/2004] [Indexed: 11/18/2022] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) fusion peptide serves as a useful model system for understanding viral/target cell fusion, at least to the lipid mixing stage. Previous solid-state NMR studies have shown that the peptide adopts an oligomeric beta-strand structure when associated with a lipid and cholesterol mixture close to that of membranes of host cells of the virus. In this study, this structure was further investigated using four different peptide constructs. In aqueous buffer solution, two of the constructs were primarily monomeric whereas the other two constructs had significant populations of oligomers/aggregates. NMR measurements for all membrane-associated peptide constructs were consistent with oligomeric beta-strand structure. Thus, constructs that are monomeric in solution can be converted to oligomers as a result of membrane association. In addition, samples prepared by very different methods had very similar NMR spectra, which indicates that the beta-strand structure is an equilibrium rather than a kinetically trapped structure. Lipid mixing assays were performed to assess the fusogenicities of the different constructs, and there was not a linear correlation between the solution oligomeric state and fusogenicity. However, the functional assays do suggest that small oligomers may be more fusogenic than either monomers or large aggregates.
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Affiliation(s)
- Jun Yang
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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27
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Lau WL, Ege DS, Lear JD, Hammer DA, DeGrado WF. Oligomerization of fusogenic peptides promotes membrane fusion by enhancing membrane destabilization. Biophys J 2004; 86:272-84. [PMID: 14695269 PMCID: PMC1303790 DOI: 10.1016/s0006-3495(04)74103-x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
A key element of membrane fusion reactions in biology is the involvement of specific fusion proteins. In many viruses, the proteins that mediate membrane fusion usually exist as homotrimers. Furthermore, they contain extended triple-helical coiled-coil domains and fusogenic peptides. It has been suggested that the coiled-coil domains present the fusogenic peptide in a conformation or geometry favorable for membrane fusion. To test the hypothesis that trimerization of fusogenic peptide is related to optimal fusion, we have designed and synthesized a triple-stranded coiled-coil X31 peptide, also known as the ccX31, which mimics the influenza virus hemagglutinin fusion peptide in the fusion-active state. We compared the membrane interactive properties of ccX31 versus the monomeric X31 fusogenic peptide. Our data show that trimerization enhances peptide-induced leakage of liposomal contents and lipid mixing. Furthermore, studies using micropipette aspiration of single vesicles reveal that ccX31 decreases lysis tension, tau(lysis), but not area expansion modulus, Ka, of phospholipid bilayers, whereas monomeric X31 peptide lowers both tau(lysis) and Ka. Our results are consistent with the hypothesis that oligomerization of fusogenic peptide promotes membrane fusion, possibly by enhancing localized destabilization of lipid bilayers.
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Affiliation(s)
- Wai Leung Lau
- Department of Biochemistry and Molecular Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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28
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Freund M, Asang C, Kammler S, Konermann C, Krummheuer J, Hipp M, Meyer I, Gierling W, Theiss S, Preuss T, Schindler D, Kjems J, Schaal H. A novel approach to describe a U1 snRNA binding site. Nucleic Acids Res 2004; 31:6963-75. [PMID: 14627829 PMCID: PMC290269 DOI: 10.1093/nar/gkg901] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
RNA duplex formation between U1 snRNA and a splice donor (SD) site can protect pre-mRNA from degradation prior to splicing and initiates formation of the spliceosome. This process was monitored, using sub-genomic HIV-1 expression vectors, by expression analysis of the glycoprotein env, whose formation critically depends on functional SD4. We systematically derived a hydrogen bond model for the complementarity between the free 5' end of U1 snRNA and 5' splice sites and numerous mutations following transient transfection of HeLa-T4+ cells with 5' splice site mutated vectors. The resulting model takes into account number, interdependence and neighborhood relationships of predicted hydrogen bond formation in a region spanning the three most 3' base pairs of the exon (-3 to -1) and the eight most 5' base pairs of the intron (+1 to +8). The model is represented by an algorithm classifying U1 snRNA binding sites which can or cannot functionally substitute SD4 with respect to Rev-mediated env expression. In a data set of 5' splice site mutations of the human ATM gene we found a significant correlation between the algorithmic classification and exon skipping (P = 0.018, chi2-test), showing that the applicability of the proposed model reaches far beyond HIV-1 splicing. However, the algorithmic classification must not be taken as an absolute measure of SD usage as it may be modified by upstream sequence elements. Upstream to SD4 we identified a fragment supporting ASF/SF2 binding. Mutating GAR nucleotide repeats within this site decreased the SD4-dependent Rev-mediated env expression, which could be balanced simply by artificially increasing the complementarity of SD4.
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Affiliation(s)
- Marcel Freund
- Institut für Virologie, Heinrich-Heine-Universität Düsseldorf, Geb. 22.21, Universitätsstrasse 1, D-40225 Düsseldorf, Germany
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29
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Caputi M, Freund M, Kammler S, Asang C, Schaal H. A bidirectional SF2/ASF- and SRp40-dependent splicing enhancer regulates human immunodeficiency virus type 1 rev, env, vpu, and nef gene expression. J Virol 2004; 78:6517-26. [PMID: 15163745 PMCID: PMC416506 DOI: 10.1128/jvi.78.12.6517-6526.2004] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The integrated human immunodeficiency virus type 1 (HIV-1) genome is transcribed in a single pre-mRNA that is alternatively spliced into more than 40 mRNAs. We characterized a novel bidirectional exonic splicing enhancer (ESE) that regulates the expression of the HIV-1 env, vpu, rev, and nef mRNAs. The ESE is localized downstream of the vpu-, env-, and nef-specific 3' splice site no. 5. SF2/ASF and SRp40 activate the ESE and are required for efficient 3' splice site usage and binding of the U1 snRNP to the downstream 5' splice site no. 4. U1 snRNP binding to the 5' splice site no. 4 is required for splicing of the rev and nef mRNAs and to increase expression of the partially spliced env mRNA. Finally, our results indicate that this ESE is necessary for the recruitment of the U1 snRNP to the 5' splice site no. 4, even when the 5' splice site and the U1 snRNA have been mutated to obtain a perfect complementary match. The ESE characterized here is highly conserved in most viral subtypes.
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MESH Headings
- Base Sequence
- Enhancer Elements, Genetic
- Exons
- Gene Expression Regulation, Viral
- Gene Products, env/genetics
- Gene Products, env/metabolism
- Gene Products, nef/genetics
- Gene Products, nef/metabolism
- Gene Products, rev/genetics
- Gene Products, rev/metabolism
- HIV-1/classification
- HIV-1/genetics
- HIV-1/physiology
- HeLa Cells
- Human Immunodeficiency Virus Proteins
- Humans
- Molecular Sequence Data
- Nuclear Proteins/metabolism
- Phosphoproteins/metabolism
- RNA Splicing
- RNA, Messenger/biosynthesis
- RNA, Viral/biosynthesis
- RNA-Binding Proteins
- Ribonucleoprotein, U1 Small Nuclear/metabolism
- Serine-Arginine Splicing Factors
- Spliceosomes
- Viral Regulatory and Accessory Proteins/genetics
- Viral Regulatory and Accessory Proteins/metabolism
- nef Gene Products, Human Immunodeficiency Virus
- rev Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- Massimo Caputi
- Department of Biology, The Johns Hopkins University, Baltimore, MD 21218, USA
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30
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Gordon LM, Mobley PW, Lee W, Eskandari S, Kaznessis YN, Sherman MA, Waring AJ. Conformational mapping of the N-terminal peptide of HIV-1 gp41 in lipid detergent and aqueous environments using 13C-enhanced Fourier transform infrared spectroscopy. Protein Sci 2004; 13:1012-30. [PMID: 15044732 PMCID: PMC2280061 DOI: 10.1110/ps.03407704] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2003] [Revised: 11/26/2004] [Accepted: 11/28/2004] [Indexed: 10/26/2022]
Abstract
The N-terminal domain of HIV-1 glycoprotein 41,000 (gp41) participates in viral fusion processes. Here, we use physical and computational methodologies to examine the secondary structure of a peptide based on the N terminus (FP; residues 1-23) in aqueous and detergent environments. (12)C-Fourier transform infrared (FTIR) spectroscopy indicated greater alpha-helix for FP in lipid-detergent sodium dodecyl sulfate (SDS) and aqueous phosphate-buffered saline (PBS) than in only PBS. (12)C-FTIR spectra also showed disordered FP conformations in these two environments, along with substantial beta-structure for FP alone in PBS. In experiments that map conformations to specific residues, isotope-enhanced FTIR spectroscopy was performed using FP peptides labeled with (13)C-carbonyl. (13)C-FTIR results on FP in SDS at low peptide loading indicated alpha-helix (residues 5 to 16) and disordered conformations (residues 1-4). Because earlier (13)C-FTIR analysis of FP in lipid bilayers demonstrated alpha-helix for residues 1-16 at low peptide loading, the FP structure in SDS micelles only approximates that found for FP with membranes. Molecular dynamics simulations of FP in an explicit SDS micelle indicate that the fraying of the first three to four residues may be due to the FP helix moving to one end of the micelle. In PBS alone, however, electron microscopy of FP showed large fibrils, while (13)C-FTIR spectra demonstrated antiparallel beta-sheet for FP (residues 1-12), analogous to that reported for amyloid peptides. Because FP and amyloid peptides each exhibit plaque formation, alpha-helix to beta-sheet interconversion, and membrane fusion activity, amyloid and N-terminal gp41 peptides may belong to the same superfamily of proteins.
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Affiliation(s)
- Larry M Gordon
- REI at Harbor-UCLA Medical Center, 124 West Carson Street, Bldg. F5 South, Torrance, CA 90502-2064, USA.
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31
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Sáez-Cirión A, Nieva JL, Gallaher WR. The hydrophobic internal region of bovine prion protein shares structural and functional properties with HIV type 1 fusion peptide. AIDS Res Hum Retroviruses 2003; 19:969-78. [PMID: 14678604 DOI: 10.1089/088922203322588323] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The conserved fusion peptide at the N-terminus of HIV-1 envelope glycoprotein gp41 is involved in the virus-cell fusion reaction and in the cytopathic effects promoted by expression in single cells. The conserved bovine prion protein 121KHVAGAAAAGAVVGGLGGYMLGSAMSR147 transmembrane region (BPrP(tm)) contains a sequence rich in Gly residues [i.e., 130GAVVGGLGGYMLGSAMSR147 (BPrP(mi))] that shows homology with HIV-1 fusion peptide. As in the case of the latter peptide, analysis of the BPrP(mi) interfacial hydrophobicity confirms that this stretch bears an intrinsic tendency to partitioning from the aqueous phase into membranes. Experimental analyses of BPrP(mi)-lipid interactions suggest several similarities between this sequence and HIV-1 fusion peptide. Infrared spectroscopy reveals a conformational plasticity of the membrane-associated prion sequence comparable to that displayed by the viral sequence. The adoption of a mainly alpha-helical structure correlates with the formation of lytic pores. This helical structure can be converted into a beta-sheet conformation by addition of calcium, a process that is accompanied by vesicle membrane fusion. In contrast, transmembrane BPrP(tm) associates with membranes in a nonlytic, mainly helical structure but also containing some random coil. Upon addition of calcium, the random coils disappear while the helical conformation remains. In the absence of membranes both prion and HIV-1 sequences form amyloid-type fibers. It is proposed that during the pathological processes induced by secreted PrPSc and its proteolytic fragments, conformational polymorphism displayed by membrane-inserted BPrP(mi) may play a role at perturbing the general architecture of the membrane lipid bilayer and inducing protein-protein aggregation at membrane surfaces. These findings suggest the existence of common mechanisms underlying cytotoxicity by PrP and HIV-1 gp41.
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Affiliation(s)
- Asier Sáez-Cirión
- Unidad de Biofísica (CSIC-UPV/EHU), and Departamento de Bioquímica, Universidad del País Vasco, 48080 Bilbao, Spain
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32
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Yang J, Weliky DP. Solid-State Nuclear Magnetic Resonance Evidence for Parallel and Antiparallel Strand Arrangements in the Membrane-Associated HIV-1 Fusion Peptide. Biochemistry 2003; 42:11879-90. [PMID: 14529300 DOI: 10.1021/bi0348157] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The HIV-1 fusion peptide serves as a useful model system for understanding viral/target cell fusion, at least to the lipid-mixing stage. Previous solid-state NMR studies have shown that the membrane-bound HIV-1 fusion peptide adopts an extended conformation in a lipid mixture close to that of host cells of the virus. In the present study, solid-state NMR REDOR methods were applied for detection of oligomeric beta strand structure. The samples were prepared under fusogenic conditions and contained equimolar amounts of two peptides, one with selective [(13)C]carbonyl labeling and the other with selective [(15)N]amide labeling. In the REDOR measurements, observation of reduced (13)C intensity due to hydrogen-bonded amide (15)N provides strong experimental evidence of oligomer formation by the membrane-associated peptide. Comparison of REDOR spectra on samples that were labeled at different residue positions suggests that there are both parallel and antiparallel arrangements of peptide strands. In the parallel arrangement, interpeptide hydrogen bonding decreases toward the C-terminus, while in the antiparallel arrangement, hydrogen bonds are observed along the entire length of residues which was probed (Gly-5 to Gly-16). For the parallel arrangement, these observations are consistent with the model in which the apolar N-terminal and central regions of the peptides penetrate into the membrane and hydrogen bond with one another while the polar C-terminus of the peptide is outside the membrane and hydrogen bonds with water. These measurements show that, at least at the end state of fusion, the peptide can adopt an oligomeric beta strand structure.
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Affiliation(s)
- Jun Yang
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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33
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Luedtke NW, Tor Y. Fluorescence-based methods for evaluating the RNA affinity and specificity of HIV-1 Rev-RRE inhibitors. Biopolymers 2003; 70:103-19. [PMID: 12925996 DOI: 10.1002/bip.10428] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
RNA plays a pivotal role in the replication of all organisms, including viral and bacterial pathogens. The development of small molecules that selectively interfere with undesired RNA activity is a promising new direction for drug design. Currently, there are no anti-HIV treatments that target nucleic acids. This article presents the HIV-1 Rev response element (RRE) as an important focus for the development of antiviral agents that target RNA. The Rev binding site on the RRE is highly conserved, even between different groups of HIV-1 isolates. Compounds that inhibit HIV replication by binding to the RRE and displacing Rev are therefore expected to retain activity across groups of genetically diverse HIV infections. Systematic evaluations of both the RRE affinity and specificity of numerous small molecule inhibitors are essential for deciphering the parameters that govern effective RRE recognition. This article discusses fluorescence-based techniques that are useful for probing a small molecule's RRE affinity and its ability to inhibit Rev-RRE binding. Rev displacement experiments can be conducted by observing the fluorescence anisotropy of a fluorescein-labeled Rev peptide, or by quantifying its displacement from a solid-phase immobilized RRE. Experiments conducted in the presence of competing nucleic acids are useful for evaluating the RRE specificity of Rev-RRE inhibitors. The discovery and characterization of new RRE ligands are described. Eilatin is a polycyclic aromatic heterocycle that has at least one binding site on the RRE (apparent Kd is approximately 0.13 microM), but it does not displace Rev upon binding the RRE (IC50 > 3 microM). In contrast, ethidium bromide and two eilatin-containing metal complexes show better consistency between their RRE affinity and their ability to displace a fluorescent Rev peptide from the RRE. These results highlight the importance of conducting orthogonal binding assays that establish both the RNA affinity of a small molecule and its ability to inhibit the function of the RNA target. Some Rev-RRE inhibitors, including ethidium bromide, Lambda-[Ru(bpy)(2)eilatin]2+, and Delta-[Ru(bpy)(2)eilatin]2+ also inhibit HIV-1 gene expression in cell cultures (IC50 = 0.2-3 microM). These (and similar) results should facilitate the future discovery and implementation of anti-HIV drugs that are targeted to viral RNA sites. In addition, a deeper general understanding of RNA-small molecule recognition will assist in the effective targeting of other therapeutically important RNA sites.
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Affiliation(s)
- Nathan W Luedtke
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0358, USA
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34
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Nieva JL, Agirre A. Are fusion peptides a good model to study viral cell fusion? BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1614:104-15. [PMID: 12873771 DOI: 10.1016/s0005-2736(03)00168-8] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Fusion peptides are hydrophobic and conserved sequences located within glycoprotein ectodomains that protrude from the virion surface. Direct participation of fusion peptides in the viral membrane fusion phenomenon has been inferred from genetic analyses showing that even a single residue substitution or a deletion within these sequences may completely block the process. However, the specific fusion peptide activities associated to the multi-step fusion mechanism are not well defined. Based on the assumption that fusion peptides are transferred into target membranes, biophysical methodologies have been applied to study integration into model membranes of synthetic fragments representing functional and non-functional sequences. From these studies, it is inferred that, following insertion, functional sequences generate target membrane perturbations and adopt specific structural arrangements within. Further characterization of these artificial systems may help in understanding the molecular processes that bring initial bilayer destabilizations to the eventual opening of a fusion pore.
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Affiliation(s)
- José L Nieva
- Unidad de Biofísica (CSIC-UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, Aptdo. 644, 48080, Bilbao, Spain.
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35
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Gabrys CM, Yang J, Weliky DP. Analysis of local conformation of membrane-bound and polycrystalline peptides by two-dimensional slow-spinning rotor-synchronized MAS exchange spectroscopy. JOURNAL OF BIOMOLECULAR NMR 2003; 26:49-68. [PMID: 12766402 DOI: 10.1023/a:1023060102409] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
2D slow-spinning, rotor-synchronized MAS exchange spectroscopy (SSRS-MASE) was applied to study local secondary structure of three structurally different peptides, two of which were membrane-bound. Each peptide was (13)C carbonyl labeled at two adjacent residues in the peptide backbone. In general, this methodology is attractive for membrane-bound peptides because of its lenient spinning, decoupling, and RF homogeneity requirements. For a single set of raw SSRS-MASE data, two linearly independent methods exist for obtaining a 2D spectrum and each spectrum can be fit to obtain conformational constraints. An approach is described for combining the results of these two fits and this method is shown to work for spectra with both resolved and unresolved labeled site resonances. A spectrum is often fit well to a few different conformations which have somewhat different values of the fitting parameter chi(2). A simple statistical theory is developed which relates the deltachi(2) difference between a local minimum and the global minimum chi(2) to the likelihood that the local minimum conformation is the correct structure. Because uncertainty in the simulated data can also contribute to the overall fitting uncertainty, an empirical method is described for incorporating the simulation uncertainty into the deltachi(2) analysis. These data analysis methods were tested on polycrystalline Ala-Gly-Gly and then applied to the membrane-bound melittin and HIV-1 fusion peptides. Melittin gave a best-fit alpha helical structure at Ala-4 while the fusion peptide gave a good-fit beta strand structure at Phe-8. The melittin analysis is in agreement with the known overall structure of this peptide.
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Affiliation(s)
- Charles M Gabrys
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
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36
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Yang R, Yang J, Weliky DP. Synthesis, enhanced fusogenicity, and solid state NMR measurements of cross-linked HIV-1 fusion peptides. Biochemistry 2003; 42:3527-35. [PMID: 12653557 DOI: 10.1021/bi027052g] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the HIV-1 gp41 and other viral fusion proteins, the minimal oligomerization state is believed to be trimeric with three N-terminal fusion peptides inserting into the membrane in close proximity. Previous studies have demonstrated that the fusion peptide by itself serves as a useful model fusion system, at least to the hemifusion stage in which the viral and target cell lipids are mixed. In the present study, HIV-1 fusion peptides were chemically synthesized and cross-linked at their C-termini to form dimers or trimers. C-terminal trimerization is their likely topology in the fusogenic form of the intact gp41 protein. The fusogenicity of the peptides was then measured in an intervesicle lipid mixing assay, and the assay results were compared to those of the monomer. For monomer, dimer, and trimer at peptide strand/lipid mol ratios between 0.0050 and 0.010, the final extent of lipid mixing for the dimer and trimer was 2-3 times greater than for the monomer. These data suggest that the higher local concentration of peptide strands in the cross-linked peptides enhances fusogenicity and that oligomerization of the fusion peptide in gp41 may enhance the rate of viral/target cell membrane fusion. For gp41, this effect is in addition to the role of the trimeric coiled-coil structure in bringing about apposition of viral and target cell membranes. NMR measurements on the membrane-associated dimeric fusion peptide were consistent with an extended structure at Phe-8, which is the same as has been observed for the membrane-bound monomer in the same lipid composition.
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Affiliation(s)
- Rong Yang
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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37
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Maddox MW, Longo ML. Conformational partitioning of the fusion peptide of HIV-1 gp41 and its structural analogs in bilayer membranes. Biophys J 2002; 83:3088-96. [PMID: 12496080 PMCID: PMC1302388 DOI: 10.1016/s0006-3495(02)75313-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Experiments have shown that the ability of the HIV-1 virus to infect cells can be greatly diminished by deactivation of the N-terminal (fusion) peptide of its glycoprotein gp41. Deactivation can be achieved by the deletion of several amino acid residues, or replacement of a hydrophobic residue with a polar residue, to form mutant variants of the wild-type peptide. We report Monte Carlo simulation studies of a simplified peptide/membrane model, representing the interaction of an HIV-1 fusion peptide (FP) and four closely related mutagens with a lipid bilayer. In agreement with experimental results, we show that FP inserts deeply into the bilayer at approximately 40 degrees to the bilayer normal. We also show a previously unreported behavior of membrane peptides, namely their equilibrium partitioning between several distinct conformations within the bilayer. We quantify this partitioning behavior and characterize each conformation in terms of its geometry, energy, and entropy. The diminished ability of FP mutagens to hemolyse and aggregate red blood cells due to their partitioning into unfavorable conformations, is also discussed. Our analysis supports a negative curvature mechanism for red blood cell hemolysis by FP. We also suggest that the small repulsive forces between surface-adsorbed peptides in opposing membrane surfaces may block aggregation.
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Affiliation(s)
- Michael W Maddox
- Department of Chemical Engineering and Materials Science, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
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38
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Kamath S, Wong TC. Membrane structure of the human immunodeficiency virus gp41 fusion domain by molecular dynamics simulation. Biophys J 2002; 83:135-43. [PMID: 12080106 PMCID: PMC1302133 DOI: 10.1016/s0006-3495(02)75155-2] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The structures of the 16-residue fusion domain (or fusion peptide, FP) of the human immunodeficiency virus gp41 fusion protein, two of its mutants, and a shortened peptide (5-16) were studied by molecular dynamics simulation in an explicit palmitoyloleoylphosphoethanolamine bilayer. The simulations showed that the active wild-type FP inserts into the bilayer approximately 44 degrees +/- 6 degrees with respect to the bilayer normal, whereas the inactive V2E and L9R mutants and the inactive 5 to 16 fragment lie on the bilayer surface. This is the first demonstration by explicit molecular dynamics of the oblique insertion of the fusion domain into lipid bilayers, and provides correlation between the mode of insertion and the fusogenic activity of these peptides. The membrane structure of the wild-type FP is remarkably similar to that of the influenza HA(2) FP as determined by nuclear magnetic resonance and electron spin resistance power saturation. The secondary structures of the wild-type FP and the two inactive mutants are quite similar, indicating that the secondary structure of this fusion domain plays little or no role in affecting the fusogenic activity of the fusion peptide. The insertion of the wild-type FP increases the thickness of the interfacial area of the bilayer by disrupting the hydrocarbon chains and extending the interfacial area toward the head group region, an effect that was not observed in the inactive FPs.
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Affiliation(s)
- Shantaram Kamath
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
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39
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Gordon LM, Mobley PW, Pilpa R, Sherman MA, Waring AJ. Conformational mapping of the N-terminal peptide of HIV-1 gp41 in membrane environments using (13)C-enhanced Fourier transform infrared spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1559:96-120. [PMID: 11853678 DOI: 10.1016/s0005-2736(01)00443-6] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The N-terminal domain of HIV-1 glycoprotein 41000 (FP; residues 1--23; AVGIGALFLGFLGAAGSTMGARSCONH(2)) participates in fusion processes underlying virus--cell infection. Here, we use physical techniques to study the secondary conformation of synthetic FP in aqueous, structure-promoting, lipid and biomembrane environments. Circular dichroism and conventional, (12)C-Fourier transform infrared (FTIR) spectroscopy indicated the following alpha-helical levels for FP in 1-palmitoyl-2-oleoylphosphatidylglycerol (POPG) liposomes-hexafluoroisopropanol (HFIP)>trifluoroethanol (TFE)>phosphate-buffered saline (PBS). (12)C-FTIR spectra also showed disordered FP structures in these environments, along with substantial beta-structures for FP in TFE or PBS. In further experiments designed to map secondary conformations to specific residues, isotope-enhanced FTIR spectroscopy was performed using a suite of FP peptides labeled with (13)C-carbonyl at multiple sites. Combining these (13)C-enhanced FTIR results with molecular simulations indicated the following model for FP in HFIP: alpha-helix (residues 3-16) and random and beta-structures (residues 1-2 and residues 17-23). Additional (13)C-FTIR analysis indicated a similar conformation for FP in POPG at low peptide loading, except that the alpha-helix extends over residues 1-16. At low peptide loading in either human erythrocyte ghosts or lipid extracts from ghosts, (13)C-FTIR spectroscopy showed alpha-helical conformations for the central core of FP (residues 5-15); on the other hand, at high peptide loading in ghosts or lipid extracts, the central core of FP assumed an antiparallel beta-structure. FP at low loading in ghosts probably inserts deeply as an alpha-helix into the hydrophobic membrane bilayer, while at higher loading FP primarily associates with ghosts as an aqueous-accessible, beta-sheet. In future studies, (13)C-FTIR spectroscopy may yield residue-specific conformations for other membrane-bound proteins or peptides, which have been difficult to analyze with more standard methodologies.
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Affiliation(s)
- Larry M Gordon
- Department of Pediatrics, Harbor-University of California at Los Angeles Medical Center, 90502-2064, USA.
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40
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Chirila TV, Rakoczy PE, Garrett KL, Lou X, Constable IJ. The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides. Biomaterials 2002; 23:321-42. [PMID: 11761152 PMCID: PMC7124374 DOI: 10.1016/s0142-9612(01)00125-9] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2000] [Accepted: 03/26/2001] [Indexed: 12/20/2022]
Abstract
Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.
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Key Words
- a, adenine
- as, antisense
- c, cytosine
- cd, cyclodextrin
- dna, deoxyribonucleic acid
- evac, poly(ethylene-co-vinyl acetate)
- g, guanine
- hart, hybrid-arrested translation
- help, high-efficiency liquid phase
- hema, 2-hydroxyethyl methacrylate
- hpma, n-(2-hydroxypropyl)methacrylamide
- ipec, interpolyelectrolyte complex
- odn, oligodeoxyribonucleotide, oligodeoxynucleotide
- pamam, polyamidoamines
- pca, polycyanoacrylates
- pdtema, n-[2-(2-pyridyldithio)]ethylmethacrylamide
- pedot, poly(3,4-ethylenedioxythiophene)
- peg, poly(ethylene glycol)
- pei, polyethyleneimine
- peo, poly(ethylene oxide)
- pga, poly(glycolic acid)
- pl, polylysine
- pla, poly(lactic acid)
- pll, poly(l-lysine)
- por, polyornithine
- ps, polyspermine
- rme, receptor-mediated endocytosis
- rna, ribonucleic acid
- mrna, messenger ribonucleic acid
- rnase, ribonuclease
- snaige, synthetic or small nucleic acids interfering with gene expression
- t, thymine
- vp, 1-vinyl-2-pyrrolidinone
- antisense strategy
- antisense oligodeoxynucleotides
- endocytosis
- drug delivery
- charged polymers
- neutral polymers
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Affiliation(s)
- Traian V Chirila
- Centre for Ophthalmology & Visual Science and Lions Eye Institute, University of Western Australia, Nedlands, Australia.
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41
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Adams O, Scheid A. Stepwise deletion of the HIV type 1 glycoprotein 41 N terminus leads to an increasing export of microvesicles containing uncleaved Env glycoprotein. AIDS Res Hum Retroviruses 2001; 17:1345-56. [PMID: 11602045 DOI: 10.1089/08892220152596605] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Deletion of two or more amino acid residues from the N terminus of HIV-1 gp41 leads to an increasing loss of cleavability of the envelope (Env) precursor on introduction of an env-expressing vector into HeLa-T4+ cells. In protein analysis, this is paralleled by the appearance of a second form of uncleaved Env precursor that is terminally sialylated. Cell-derived microvesicles that preferentially incorporate this form of Env precursor were found in the culture medium. The same applies to a mutant with a nonfunctional cleavage site, indicating that a pathway by which uncleaved Env glycoprotein leaves the cell exists. The amount of exported glycoprotein is augmented as compared with wild-type Env. Transfection with a wild-type Env-expressing vector leads to the presence of extracellular microvesicles that contain only the transmembrane domain of HIV-1 Env. Microvesicles derived from wild-type Env and mutant Env contain sialylated glycoproteins that are resistant to exo- and endoglycosidase treatment unless the particles have been previously lysed by detergent. This raises the possibility that the C-terminal domains of the glycoproteins are exposed on the surface of the exported microvesicles.
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Affiliation(s)
- O Adams
- Institut für Medizinische Mikrobiologie und Virologie, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
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Krummheuer J, Lenz C, Kammler S, Scheid A, Schaal H. Influence of the small leader exons 2 and 3 on human immunodeficiency virus type 1 gene expression. Virology 2001; 286:276-89. [PMID: 11485396 DOI: 10.1006/viro.2001.0974] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human immunodeficiency virus type 1 (HIV-1) uses an elaborate alternative splicing pattern for the generation of both the 1.8-kb as well as the 4-kb classes of mRNA. An additional diversity of transcripts in both classes is created by the optional inclusion of the small exons 2 and 3 in the leader sequence. To analyze a possible influence of these leader exons on HIV-1 gene expression, several series of expression vectors with different leaders were constructed, expressing either Rev and Env or a heterologous coding sequence, i.e., the chloramphenicol acetyl transferase (CAT) ORF. Transfection experiments of HeLa-T4(+) cells revealed for all series of constructs that mRNA as well as protein expression was stimulated by the presence of exon 2 and reduced by exon 3. The function of the leader exons 2 and 3 is neither dependent on the regulatory proteins Tat or Rev nor on viral coding sequences. Neither transcription rates nor stability of polyadenylated RNAs were found to be responsible for the different levels of steady-state mRNA. When either exon 2 or 3 was inserted into a heterologous intron, processing of the primary transcripts generated identical mRNA species while maintaining the differences in exon 2/3-dependent mRNA steady-state levels. These results may be explained by exon-specific nuclear RNA degradation rates, as also indicated by results from an in vitro degradation assay using a HeLa nuclear extract.
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MESH Headings
- Alternative Splicing
- Cell Line
- Cytoplasm/genetics
- Exons
- Gene Expression Regulation, Viral
- Gene Products, tat/genetics
- Gene Products, tat/metabolism
- Genetic Vectors
- HIV Long Terminal Repeat
- HIV-1/genetics
- HIV-1/metabolism
- HeLa Cells
- Humans
- Introns
- RNA Stability
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Nuclear
- RNA, Viral/genetics
- RNA, Viral/metabolism
- Transcription, Genetic
- Transcriptional Activation
- Viral Proteins/genetics
- Viral Proteins/metabolism
- tat Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- J Krummheuer
- Institut für Medizinische Mikrobiologie und Virologie, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
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Yang J, Gabrys CM, Weliky DP. Solid-state nuclear magnetic resonance evidence for an extended beta strand conformation of the membrane-bound HIV-1 fusion peptide. Biochemistry 2001; 40:8126-37. [PMID: 11434782 DOI: 10.1021/bi0100283] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Solid-state nuclear magnetic resonance (NMR) spectroscopy was applied to the membrane-bound form of a synthetic peptide representing the 23-residue N-terminal fusion peptide domain of the HIV-1 gp41 envelope glycoprotein. 1D solid-state NMR line width measurements of singly 13C carbonyl labeled peptides showed that a significant population of the membrane-bound peptide is well-structured in its N-terminal and central regions while the C-terminus has more disorder. There was some dependence of line width on lipid composition, with narrower line widths and hence greater structural order observed for a lipid composition comparable to that found in the virus and its target T cells. In the more ordered N-terminal and central regions of the peptide, the 13C carbonyl chemical shifts are consistent with a nonhelical membrane-bound conformation. Additional evidence for a beta strand membrane-bound conformation was provided by analysis of 2D rotor-synchronized magic angle spinning NMR spectra of doubly 13C carbonyl labeled peptides. Lipid mixing and aqueous contents leakage assays were applied to demonstrate the fusogenicity of the peptide under conditions comparable to those used for the solid-state NMR sample preparation.
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Affiliation(s)
- J Yang
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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Sparacio S, Pfeiffer T, Schaal H, Bosch V. Generation of a flexible cell line with regulatable, high-level expression of HIV Gag/Pol particles capable of packaging HIV-derived vectors. Mol Ther 2001; 3:602-12. [PMID: 11319923 DOI: 10.1006/mthe.2001.0296] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
HIV-derived vectors are of potential clinical relevance due to their ability to transduce nondividing cells in vitro and in vivo. However, the generation of cell lines stably and reproducibly expressing high amounts of defined subviral particles, capable of packaging and transducing HIV-derived vectors, has been hampered by the cytotoxicity of some of the required gene products, in particular of the HIV-1 protease. The successful use of regulatable gene expression systems to overcome this problem requires that the remaining basally expressed gene product activity is below the threshold for cytotoxicity. To try to achieve this, we have consecutively introduced appropriate plasmids, encoding HIV rev and HIV gag/pol gene products, each under the control of separate ecdysone-inducible promoters, into human 293 cells. Using a protocol in which a specific HIV protease inhibitor, Saquinavir, was continuously present in the culture medium during selection, we could generate stable cell lines inducibly expressing high amounts of subviral particles. A cell line, termed 293-Rev/Gag/Pol(i), which has been characterized in more detail, inducibly releases, within 48 h postinduction, high amounts of HIV Gag/Pol particles (about 10 microg CA/ml). These HIV Gag/Pol particles can package and transduce third-generation HIV vectors to high titers. Thus, in addition to other applications, the 293-Rev/Gag/Pol(i) cell line represents a "founder" packaging cell line which, depending on the requirement, can be further modified to include specific transgene-encoding vector and targeting glycoprotein genes.
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Affiliation(s)
- S Sparacio
- Forschungsschwerpunkt Angewandte Tumorvirologie, F0200, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 242, Heidelberg, 69120, Germany
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Mobley PW, Pilpa R, Brown C, Waring AJ, Gordon LM. Membrane-perturbing domains of HIV type 1 glycoprotein 41. AIDS Res Hum Retroviruses 2001; 17:311-27. [PMID: 11242518 DOI: 10.1089/08892220150503681] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Structural and functional studies were performed to assess the membrane actions of peptides based on HIV-1 glycoprotein 41,000 (gp41). Previous site-directed mutagenesis of gp41 has shown that amino acid changes in either the N-terminal fusion or N-leucine zipper region depressed viral infection and syncytium formation, while modifications in the C-leucine zipper domain both increased and decreased HIV fusion. Here, synthetic peptides were prepared corresponding to the N-terminal fusion region (FP-I; gp41 residues 519-541), the nearby N-leucine zipper domain (DP-107; gp41 residues 560-597), and the C-leucine zipper domain (DP-178; gp41 residues 645-680). With erythrocytes, FP-I or DP-107 induced dose-dependent hemolysis and promoted cell aggregation; FP-I was more hemolytic than DP-107, but each was equally effective in aggregating cells. DP-178 produced neither hemolysis nor aggregation, but blocked either FP-I- or DP-107-induced hemolysis and aggregation. Combined with previous nuclear magnetic resonance and Fourier transform infrared spectroscopic results, circular dichroism (CD) spectroscopy showed that the alpha-helicity for these peptides in solution decreased in the order: DP-107 >> DP-178 > FP-I. CD analysis also indicated binding of DP-178 to either DP-107 or FP-I. Consequently, DP-178 may inhibit the membrane actions mediated by either FP-I or DP-107 through direct peptide interactions in solution. These peptide results suggest that the corresponding N-terminal fusion and N-leucine zipper regions participate in HIV infection, by promoting membrane perturbations underlying the merging of the viral envelope with the cell surface. Further, the C-leucine zipper domain in "prefusion" HIV may inhibit these membrane activities by interacting with the N-terminal fusion and N-leucine zipper domains in unactivated gp41. Last, exogenous DP-178 may bind to the N-terminal and N-leucine zipper domains of gp41 that become exposed on HIV stimulation, thereby preventing the fusogenic actions of these gp41 regions leading to infection.
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Affiliation(s)
- P W Mobley
- Chemistry Department, California State Polytechnic University, Pomona 91768, USA
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Kammler S, Leurs C, Freund M, Krummheuer J, Seidel K, Tange TO, Lund MK, Kjems J, Scheid A, Schaal H. The sequence complementarity between HIV-1 5' splice site SD4 and U1 snRNA determines the steady-state level of an unstable env pre-mRNA. RNA (NEW YORK, N.Y.) 2001; 7:421-34. [PMID: 11333022 PMCID: PMC1370098 DOI: 10.1017/s1355838201001212] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
HIV-1 env expression from certain subgenomic vectors requires the viral regulatory protein Rev, its target sequence RRE, and a 5' splice site upstream of the env open reading frame. To determine the role of this splice site in the 5'-splice-site-dependent Rev-mediated env gene expression, we have subjected the HIV-1 5' splice site, SD4, to a mutational analysis and have analyzed the effect of those mutations on env expression. The results demonstrate that the overall strength of hydrogen bonding between the 5' splice site, SD4, and the free 5' end of the U1 snRNA correlates with env expression efficiency, as long as env expression is suboptimal, and that a continuous stretch of 14 hydrogen bonds can lead to full env expression, as a result of stabilizing the pre-mRNA. The U1 snRNA-mediated stabilization is independent of functional splicing, as a mismatch in position +1 of the 5' splice site that led to loss of detectable amounts of spliced transcripts did not preclude stabilization and expression of the unspliced env mRNA, provided that Rev enables its nuclear export. The nucleotides capable of participating in U1 snRNA:pre-mRNA interaction include positions -3 to +8 of the 5' splice site and all 11 nt constituting the single-stranded 5' end of U1 snRNA. Moreover, env gene expression is significantly decreased upon the introduction of point mutations in several upstream GAR nucleotide motifs, which are mediating SF2/ASF responsiveness in an in vitro splicing assay. This suggests that the GAR sequences may play a role in stabilizing the pre-mRNA by sequestering U1 snRNP to SD4.
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Affiliation(s)
- S Kammler
- Institut für Medizinische Mikrobiologie und Virologie, Heinrich-Heine-Universität Düsseldorf, Germany
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Abstract
Although membrane fusion occurs ubiquitously and continuously in all eukaroytic cells, little is known about the mechanism that governs lipid bilayer fusion associated with any intracellular fusion reactions. Recent studies of the fusion of enveloped viruses with host cell membranes have helped to define the fusion process. The identification and characterization of key proteins involved in fusion reactions have mainly driven recent advances in our understanding of membrane fusion. The most important denominator among the fusion proteins is the fusion peptide. In this review, work done in the last few years on the molecular mechanism of viral membrane fusion will be highlighted, focusing in particular on the role of the fusion peptide and the modification of the lipid bilayer structure. Much of what is known regarding the molecular mechanism of viral membrane fusion has been gained using liposomes as model systems in which the molecular components of the membrane and the environment are strictly controlled. Many amphilphilic peptides have a high affinity for lipid bilayers, but only a few sequences are able to induce membrane fusion. The presence of alpha-helical structure in at least part of the fusion peptide is strongly correlated with activity whereas, beta-structure tends to be less prevalent, associated with non-native experimental conditions, and more related to vesicle aggregation than fusion. The specific angle of insertion of the peptides into the membrane plane is also found to be an important characteristic for the fusion process. A shallow penetration, extending only to the central aliphatic core region, is likely responsible for the destabilization of the lipids required for coalescence of the apposing membranes and fusion.
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Affiliation(s)
- I Martin
- Laboratoire de Chimie-Physique des Macromolécules aux Interfaces (LPCMI) CP206/2, Université Libre de Bruxelles, Brussels, Belgium.
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Taylor SE, Desbat B, Blaudez D, Jacobi S, Chi LF, Fuchs H, Schwarz G. Structure of a fusion peptide analogue at the air-water interface, determined from surface activity, infrared spectroscopy and scanning force microscopy. Biophys Chem 2000; 87:63-72. [PMID: 11036970 DOI: 10.1016/s0301-4622(00)00182-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have investigated a point mutant of the HIV-1 fusion peptide in a compressed monolayer at the air-water interface. A variety of surface sensitive techniques were applied to study structural features under conditions mimicking the hydrophobic/hydrophilic environment of a biomembrane. Possible partitioning into the aqueous bulk phase and molecular areas were examined by surface activity based mass conservation plots. This shows that the peptide is practically fully accumulated in the interface. Secondary structure and orientation was analyzed by means of polarized infrared reflectivity. Brewster angle microscopy and scanning force microscopy contributed nanostructural images. At low surface pressures the molecules form anti-parallel beta-sheets lying flat on the interface. Upon a moderate increase of the lateral pressure a flat beta-turn structure appears with inter- and intramolecular H-bonds. We also observed aggregates forming fingerprint-like structures with a diameter of approximately double the hydrophobic length of a beta-turn conformation. Beyond approximately 18 mN m(-1) the beta-turns straighten up. The lowest measured tilt angle was 45 degrees at 36 mN m(-1).
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Affiliation(s)
- S E Taylor
- Department of Biophysical Chemistry, Biocenter of the University, Basel, Switzerland
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49
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Adams O, Schaal H, Scheid A. Natural variation in the amino acid sequence around the HIV type 1 glycoprotein 160 cleavage site and its effect on cleavability, subunit association, and membrane fusion. AIDS Res Hum Retroviruses 2000; 16:1235-45. [PMID: 10957721 DOI: 10.1089/08892220050117005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
To assess the natural variation of the structure of the cleavage site as well as the N-terminal region of gp41 for the cytopathogenicity of HIV-1, syncytium-inducing (SI) and non-syncytium-inducing (NSI) virus isolates were obtained from HIV-1-infected patients. In addition, the coreceptor usage of the isolates was determined by infection of primary macrophages and PM-1 cells. DNA sequences encoding the C-terminal 41 amino acid residues of gp120 and the 64 amino acid N-terminal residues of gp41 were amplified by the polymerase chain reaction and inserted into the Env expression vector pNLA1. When transfected into HeLa-T4(+) cells, all the recombinant plasmids, including those with inserts from NSI isolates, led to the formation of processed glycoprotein and to syncytium formation. One construct displayed significant lowered fusion capacity and had an amino acid exchange in the first position of the gp41 N terminus (gp41, 512A-->S) leading to a decreased association of the SU and TM subunits. Four constructs derived from two isolates of the same patient showed an unusual gp41 N terminus (gp41, 514G-->P) and a slightly diminished fusion capacity due to a decreased cleavability. This indicates that the major determinants for the SI and NSI phenotypes are not located around the gp160 cleavage site and that the N terminus of gp41 plays a minor role in the processing and fusion capacity of wild-type HIV-1 isolates.
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Affiliation(s)
- O Adams
- Institut für Medizinische Mikrobiologie und Virologie, Heinrich-Heine-Universität, Düsseldorf, Germany.
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Suárez T, Gallaher WR, Agirre A, Goñi FM, Nieva JL. Membrane interface-interacting sequences within the ectodomain of the human immunodeficiency virus type 1 envelope glycoprotein: putative role during viral fusion. J Virol 2000; 74:8038-47. [PMID: 10933713 PMCID: PMC112336 DOI: 10.1128/jvi.74.17.8038-8047.2000] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have identified a region within the ectodomain of the fusogenic human immunodeficiency virus type 1 (HIV-1) gp41, different from the fusion peptide, that interacts strongly with membranes. This conserved sequence, which immediately precedes the transmembrane anchor, is not highly hydrophobic according to the Kyte-Doolittle hydropathy prediction algorithm, yet it shows a high tendency to partition into the membrane interface, as revealed by the Wimley-White interfacial hydrophobicity scale. We have investigated here the membrane effects induced by NH(2)-DKWASLWNWFNITNWLWYIK-CONH(2) (HIV(c)), the membrane interface-partitioning region at the C terminus of the gp41 ectodomain, in comparison to those caused by NH(2)-AVGIGALFLGFLGAAGSTMGARS-CONH(2) (HIV(n)), the fusion peptide at the N terminus of the subunit. Both HIV(c) and HIV(n) were seen to induce membrane fusion and permeabilization, although lower doses of HIV(c) were required for comparable effects to be detected. Experiments in which equimolar mixtures of HIV(c) and HIV(n) were used indicated that both peptides may act in a cooperative way. Peptide-membrane and peptide-peptide interactions underlying those effects were further confirmed by analyzing the changes in fluorescence of peptide Trp residues. Replacement of the first three Trp residues by Ala, known to render a defective gp41 phenotype unable to mediate both cell-cell fusion and virus entry, also abrogated the HIV(c) ability to induce membrane fusion or form complexes with HIV(n) but not its ability to associate with vesicles. Hydropathy analysis indicated that the presence of two membrane-partitioning stretches separated by a collapsible intervening sequence is a common structural motif among other viral envelope proteins. Moreover, sequences with membrane surface-residing residues preceding the transmembrane anchor appeared to be a common feature in viral fusion proteins of several virus families. According to our experimental results, such a feature might be related to their fusogenic function.
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Affiliation(s)
- T Suárez
- Unidad de Biofísica (CSIC-UPV/EHU) and Departamento de Bioquímica, Universidad del País Vasco, 48080 Bilbao, Spain
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