scholarly journals Retrovirus Glycoprotein Functionality Requires Proper Alignment of the Ectodomain and the Membrane-Proximal Cytoplasmic Tail

2013 ◽  
Vol 87 (23) ◽  
pp. 12805-12813 ◽  
Author(s):  
Sanath Kumar Janaka ◽  
Devon A. Gregory ◽  
Marc C. Johnson
Keyword(s):  
Leukemia Virus ◽  
Coiled Coil ◽  
Cytoplasmic Tail ◽  
Wild Type ◽  
Virus Envelope ◽  
Viral Glycoproteins ◽  
Similar Phenotype ◽  
Membrane Spanning ◽  
Hiv 1 ◽  
Murine Leukemia

Nonnative viral glycoproteins, including Friend murine leukemia virus envelope (F-MLV Env) are actively recruited to HIV-1 assembly sites by an unknown mechanism. Because interactions with the lipid microenvironment at budding sites could contribute to recruitment, we examined the contribution of the hydrophobicity of the F-MLV Env membrane-spanning domain (MSD) to its incorporation into HIV-1 particles. A series of F-MLV Env mutants that added or deleted one, two, or three leucines in the MSD were constructed. All six mutants retained the ability to be incorporated into HIV-1 particles, but the −1L, −2L, −3L, +1L, and +2L mutants were not capable of producing infectious particles. Surprisingly, the +3L Env glycoprotein was able to produce infectious particles and was constitutively fusogenic. However, when the cytoplasmic tail domains (CTDs) in the Env constructs were deleted, all six of the MSD mutants were able to produce infectious particles. Further mutational analyses revealed that the first 10 amino acids of the CTD is a critical regulator of infectivity. A similar phenotype was observed in HIV-1 Env upon addition of leucines in the MSD, with +1 and +2 leucine mutations greatly reducing Env activity, but +3 leucine mutations behaving similar to the wild type. Unlike F-MLV Env (+1L and +2L), HIV-1 Env (+1L and +2L) infectivity was not restored by deletion of the CTD. We hypothesize that the CTD forms a coiled-coil that disrupts the protein's functionality if it is not in phase with the trimer interface of the ectodomain.

scholarly journals Characterizing the Murine Leukemia Virus Envelope Glycoprotein Membrane-Spanning Domain for Its Roles in Interface Alignment and Fusogenicity

2015 ◽  
Vol 89 (24) ◽  
pp. 12492-12500 ◽  
Author(s):  
Daniel J. Salamango ◽  
Marc C. Johnson
Keyword(s):  
Amino Acids ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Tail Domain ◽  
Virus Envelope ◽  
C Terminus ◽  
Viral Glycoproteins ◽  
N Terminus ◽  
Membrane Spanning ◽  
Murine Leukemia

ABSTRACTThe membrane-proximal region of murine leukemia virus envelope (Env) is a critical modulator of its functionality. We have previously shown that the insertion of one amino acid (+1 leucine) within the membrane-spanning domain (MSD) abolished protein functionality in infectivity assays. However, functionality could be restored to this +1 leucine mutant by either inserting two additional amino acids (+3 leucine) or by deleting the cytoplasmic tail domain (CTD) in the +1 leucine background. We inferred that the ectodomain and CTD have protein interfaces that have to be in alignment for Env to be functional. Here, we made single residue deletions to the Env mutant with the +1 leucine insertion to restore the interface alignment (gain of functionality) and therefore define the boundaries of the two interfaces. We identified the glycine-proline pairs near the N terminus (positions 147 and 148) and the C terminus (positions 159 and 160) of the MSD as being the boundaries of the two interfaces. Deletions between these pairs restored function, but deletions outside of them did not. In addition, the vast majority of the single residue deletions regained function if the CTD was deleted. The exceptions were four hydroxyl-containing amino acid residues (T139, T140, S143, and T144) that reside in the ectodomain interface and the proline at position 148, which were all indispensable for functionality. We hypothesize that the hydroxyl-containing residues at positions T139 and S143 could be a driving force for stabilizing the ectodomain interface through formation of a hydrogen-bonding network.IMPORTANCEThe membrane-proximal external region (MPER) and membrane-spanning domains (MSDs) of viral glycoproteins have been shown to be critical for regulating glycoprotein fusogenicity. However, the roles of these two domains are poorly understood. We report here that point deletions and insertions within the MPER or MSD result in functionally inactive proteins. However, when the C-terminal tail domain (CTD) is deleted, the majority of the proteins remain functional. The only residues that were found to be critical for function regardless of the CTD were four hydroxyl-containing amino acids located at the C terminus of the MPER (T139 and T140) and at the N terminus of the MSD (S143 and T144) and a proline near the beginning of the MSD (P148). We demonstrate that hydrogen-bonding at positions T139 and S143 is critical for protein function. Our findings provide novel insights into the role of the MPER in regulating fusogenic activity of viral glycoproteins.

scholarly journals Pseudotyping Incompatibility between HIV-1 and Gibbon Ape Leukemia Virus Env Is Modulated by Vpu

2009 ◽  
Vol 84 (6) ◽  
pp. 2666-2674 ◽  
Author(s):  
Tiffany M. Lucas ◽  
Terri D. Lyddon ◽  
Paula M. Cannon ◽  
Marc C. Johnson
Keyword(s):  
Leukemia Virus ◽  
Cytoplasmic Tail ◽  
Viral Particles ◽  
Immunodeficiency Virus ◽  
Env Protein ◽  
Membrane Spanning ◽  
Gibbon Ape Leukemia Virus ◽  
Hiv 1 ◽  
Murine Leukemia

ABSTRACT The Env protein from gibbon ape leukemia virus (GaLV) has been shown to be incompatible with human immunodeficiency virus type 1 (HIV-1) in the production of infectious pseudotyped particles. This incompatibility has been mapped to the C-terminal cytoplasmic tail of GaLV Env. Surprisingly, we found that the HIV-1 accessory protein Vpu modulates this incompatibility. The infectivity of HIV-1 pseudotyped with murine leukemia virus (MLV) Env was not affected by Vpu. However, the infectivity of HIV-1 pseudotyped with an MLV Env with the cytoplasmic tail from GaLV Env (MLV/GaLV Env) was restricted 50- to 100-fold by Vpu. A Vpu mutant containing a scrambled membrane-spanning domain, VpuRD, was still able to restrict MLV/GaLV Env, but mutation of the serine residues at positions 52 and 56 completely alleviated the restriction. Loss of infectivity appeared to be caused by reduced MLV/GaLV Env incorporation into viral particles. The mechanism of this downmodulation appears to be distinct from Vpu-mediated CD4 downmodulation because Vpu-expressing cells that failed to produce infectious HIV-1 particles nonetheless continued to display robust surface MLV/GaLV Env expression. In addition, if MLV and HIV-1 were simultaneously introduced into the same cells, only the HIV-1 particle infectivity was restricted by Vpu. Collectively, these data suggest that Vpu modulates the cellular distribution of MLV/GaLV Env, preventing its recruitment to HIV-1 budding sites.

scholarly journals Cytoplasmic Tail of Moloney Murine Leukemia Virus Envelope Protein Influences the Conformation of the Extracellular Domain: Implications for Mechanism of Action of the R Peptide

2003 ◽  
Vol 77 (2) ◽  
pp. 1281-1291 ◽  
Author(s):  
Hector C. Aguilar ◽  
W. French Anderson ◽  
Paula M. Cannon
Keyword(s):  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Cytoplasmic Tail ◽  
Moloney Murine Leukemia Virus ◽  
Virus Envelope ◽  
Peptide Cleavage ◽  
Virus Envelope Protein ◽  
Env Protein ◽  
Membrane Spanning ◽  
Murine Leukemia

ABSTRACT The envelope (Env) protein of Moloney murine leukemia virus (MoMuLV) is a homotrimeric complex whose monomers consist of linked surface (SU) and transmembrane (TM) proteins cleaved from a precursor protein by a cellular protease. In addition, a significant fraction of virion-associated TM is further processed by the viral protease to remove the C-terminal 16 amino acids of the cytoplasmic domain, the R peptide. This cleavage greatly enhances the fusogenicity of the protein and is necessary for the formation of a fully functional Env protein complex. We have previously proposed that R peptide cleavage enhances fusogenicity by altering the conformation of the ectodomain of the protein (Y. Zhao et al., J. Virol. 72:5392-5398, 1998). Using a series of truncation and point mutants of MoMuLV Env, we now provide direct biochemical and immunological evidence that the cytoplasmic tail and the membrane-spanning region of Env can influence the overall structure of the ectodomain of the protein and alter the strength of the SU-TM interaction. The R-peptide-truncated form of the protein, in particular, exhibits a markedly different conformation than the full-length protein.

scholarly journals Sequences in the Cytoplasmic Tail of the Gibbon Ape Leukemia Virus Envelope Protein That Prevent Its Incorporation into Lentivirus Vectors

2001 ◽  
Vol 75 (9) ◽  
pp. 4129-4138 ◽  
Author(s):  
Ilias Christodoulopoulos ◽  
Paula M. Cannon
Keyword(s):  
Leukemia Virus ◽  
Cytoplasmic Tail ◽  
Viral Fusion ◽  
Virus Envelope ◽  
Peptide Cleavage ◽  
Long Range Interactions ◽  
Virus Envelope Protein ◽  
Lentivirus Vectors ◽  
Membrane Spanning ◽  
Gibbon Ape Leukemia Virus

ABSTRACT Pseudotyping retrovirus and lentivirus vectors with different viral fusion proteins is a useful strategy to alter the host range of the vectors. Although lentivirus vectors are efficiently pseudotyped by Env proteins from several different subtypes of murine leukemia virus (MuLV), the related protein from gibbon ape leukemia virus (GaLV) does not form functional pseudotypes. We have determined that this arises because of an inability of GaLV Env to be incorporated into lentivirus vector particles. By exploiting the homology between the GaLV and MuLV Env proteins, we have mapped the determinants of incompatibility in the GaLV Env. Three modifications that allowed GaLV Env to pseudotype human immunodeficiency virus type 1 particles were identified: removal of the R peptide (C-terminal half of the cytoplasmic domain), replacement of the whole cytoplasmic tail with the corresponding MuLV region, and mutation of two residues upstream of the R peptide cleavage site. In addition, we have previously proposed that removal of the R peptide from MuLV Env proteins enhances their fusogenicity by transmitting a conformational change to the ectodomain of the protein (Y. Zhao et al., J. Virol. 72:5392–5398, 1998). Our analysis of chimeric MuLV/GaLV Env proteins provides further evidence in support of this model and suggests that proper Env function involves both interactions within the cytoplasmic tail and more long-range interactions between the cytoplasmic tail, the membrane-spanning region, and the ectodomain of the protein.

scholarly journals Cleavage of the Murine Leukemia Virus Transmembrane Env Protein by Human Immunodeficiency Virus Type 1 Protease: Transdominant Inhibition by Matrix Mutations

1998 ◽  
Vol 72 (12) ◽  
pp. 9621-9627 ◽  
Author(s):  
Rosemary E. Kiernan ◽  
Eric O. Freed
Keyword(s):  
Human Immunodeficiency Virus ◽  
Human Immunodeficiency Virus Type ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Wild Type ◽  
Immunodeficiency Virus ◽  
Env Protein ◽  
Hiv 1 ◽  
Murine Leukemia

ABSTRACT We have identified mutations in the human immunodeficiency virus type 1 (HIV-1) matrix protein (MA) which block infectivity of virions pseudotyped with murine leukemia virus (MuLV) envelope (Env) glycoproteins without affecting infectivity conferred by HIV-1 Env or vesicular stomatitis virus G glycoproteins. This inhibition is very potent and displays a strong transdominant effect; infectivity is reduced more than 100-fold when wild-type and mutant molecular clones are cotransfected at a 1:1 ratio. This phenomenon is observed with both ecotropic and amphotropic MuLV Env. The MA mutations do not affect the incorporation of MuLV Env into virions. We demonstrate that in HIV-1 virions pseudotyped with MuLV Env, the HIV-1 protease (PR) efficiently catalyzes the cleavage of the p15(E) transmembrane (TM) protein to p12(E). Immunoprecipitation analysis of pseudotyped virions reveals that the mutant MA blocks this HIV-1 PR-mediated cleavage of MuLV TM. Furthermore, the transdominant inhibition exerted by the mutant MA on wild-type infectivity correlates with the relative level of p15(E) cleavage. Consistent with the hypothesis that abrogation of infectivity imposed by the mutant MA is due to inhibition of p15(E) cleavage, mutant virions are significantly more infectious when pseudotyped with a truncated p12(E) form of MuLV Env. These results indicate that HIV-1 Gag sequences can influence the viral PR-mediated processing of the MuLV TM Env protein p15(E). These findings have implications for the development of HIV-1-based retroviral vectors pseudotyped with MuLV Env, since p15(E) cleavage is essential for activating membrane fusion and virus infectivity.

scholarly journals A Hydrophobic Patch in Ecotropic Murine Leukemia Virus Envelope Protein Is the Putative Binding Site for a Critical Tyrosine Residue on the Cellular Receptor

1999 ◽  
Vol 73 (12) ◽  
pp. 10164-10172 ◽  
Author(s):  
Tatiana Zavorotinskaya ◽  
Lorraine M. Albritton
Keyword(s):  
Envelope Protein ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Wild Type Virus ◽  
Wild Type ◽  
Virus Binding ◽  
Virus Envelope ◽  
Virus Envelope Protein ◽  
Putative Binding Site ◽  
Murine Leukemia

ABSTRACT In the receptor for ecotropic murine leukemia viruses, tyrosine 235 contributes a critical hydrophobic side chain to the virus-receptor interaction (14). Here we report that tryptophan 142 in ecotropic Moloney murine leukemia virus envelope protein is essential to virus binding and infection. Replacement of tryptophan 142 by alanine or serine resulted in misfolding. However, replacement by methionine (W142M) allowed correct folding of the majority of glycoprotein molecules. W142M virus showed a marked reduction in virus binding and was almost noninfectious, suggesting that tryptophan 142 is involved in receptor binding. In contrast, W142Y virus containing a replacement of tryptophan 142 with an aromatic residue (tyrosine) was as efficient as wild-type virus in infection and binding of cells expressing the wild-type receptor. However, W142Y virus was 100-fold less efficient than wild-type virus in infection of cells expressing a mutant receptor containing tryptophan instead of the critical tyrosine. These results strongly support tryptophan 142 being an essential residue on the virus envelope protein that interacts directly with the critical hydrophobic residue at position 235 of the ecotropic receptor. Tryptophan 142 forms one side of a shallow hydrophobic pocket on the surface of the envelope protein, suggesting that it might comprise the complete putative binding site for tyrosine 235. We discuss the implications of our findings with respect to two models of the envelope protein trimer. Interestingly, both models place tryptophan 142 at the interface between adjacent subunits of the trimer.

scholarly journals Palmitoylation of the Murine Leukemia Virus Envelope Protein Is Critical for Lipid Raft Association and Surface Expression

2002 ◽  
Vol 76 (23) ◽  
pp. 11845-11852 ◽  
Author(s):  
Min Li ◽  
Chinglai Yang ◽  
Suxiang Tong ◽  
Armin Weidmann ◽  
Richard W. Compans
Keyword(s):  
Lipid Rafts ◽  
Lipid Raft ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Viral Fusion ◽  
Deficient Mutant ◽  
Wild Type ◽  
Virus Envelope ◽  
Env Protein ◽  
Murine Leukemia

ABSTRACT To investigate the association of the murine leukemia virus (MuLV) Env protein with lipid rafts, we compared wild-type and palmitoylation-deficient mutant Env proteins by using extraction with the mild detergent Triton X-100 (TX-100) followed by a sucrose gradient flotation assay. We found that the wild-type MuLV Env protein was resistant to ice-cold TX-100 treatment and floated to the top of the gradients. In contrast, we observed that the palmitoylation-deficient mutant Env protein was mostly soluble when extracted by ice-cold TX-100 and stayed at the bottom of the gradients. Both the wild-type and mutant Env proteins were found to be soluble when treated with methyl-β-cyclodextrin before extraction with ice-cold TX-100 or when treated with ice-cold octyl-β-glucoside instead of TX-100. These results indicate that the MuLV Env protein is associated with lipid rafts and that palmitoylation of the Env protein is critical for lipid raft association. Although the palmitoylation-deficient Env mutant was synthesized at a level similar to that of the wild-type Env, it was found to be expressed at reduced levels on the cell surface. We observed syncytium formation activity with both the wild-type and mutant Env proteins, indicating that palmitoylation or raft association is not required for MuLV viral fusion activity.

scholarly journals Infectivity of Moloney Murine Leukemia Virus Defective in Late Assembly Events Is Restored by Late Assembly Domains of Other Retroviruses

2000 ◽  
Vol 74 (16) ◽  
pp. 7250-7260 ◽  
Author(s):  
Bing Yuan ◽  
Stephen Campbell ◽  
Eran Bacharach ◽  
Alan Rein ◽  
Stephen P. Goff
Keyword(s):  
Murine Leukemia Virus ◽  
Deletion Mutant ◽  
Leukemia Virus ◽  
Spherical Particles ◽  
Moloney Murine Leukemia Virus ◽  
Wild Type ◽  
Independent Manner ◽  
Gag Protein ◽  
Hiv 1 ◽  
Murine Leukemia

ABSTRACT The p12 region of the Moloney murine leukemia virus (M-MuLV) Gag protein contains a PPPY motif important for efficient virion assembly and release. To probe the function of the PPPY motif, a series of insertions of homologous and heterologous motifs from other retroviruses were introduced at various positions in a mutantgag gene lacking the PPPY motif. The assembly defects of the PPPY deletion mutant could be rescued by insertion of a wild-type PPPY motif and flanking sequences at several ectopic positions in the Gag protein. The late assembly domain (L-domain) of Rous sarcoma virus (RSV) or human immunodeficiency virus type 1 (HIV-1) could also fully or partially restore M-MuLV assembly when introduced into matrix, p12, or nucleocapsid domains of the mutant M-MuLV Gag protein lacking the PPPY motif. Strikingly, mutant viruses carrying the RSV or the HIV-1 L-domain at the original location of the deleted PPPY motif were replication competent in rodent cells. These data suggest that the PPPY motif of M-MuLV acts in a partially position-independent manner and is functionally interchangeable with L-domains of other retroviruses. Electron microscopy studies revealed that deletion of the entire p12 region resulted in the formation of tube-like rather than spherical particles. Remarkably, the PPPY deletion mutant formed chain structures composed of multiple viral particles linked on the cell surface. Many of the mutants with heterologous L-domains released virions with wild-type morphology.

scholarly journals Wild-Type and YMDD Mutant Murine Leukemia Virus Reverse Transcriptases Are Resistant to 2′,3′-Dideoxy-3′-Thiacytidine

2000 ◽  
Vol 74 (14) ◽  
pp. 6669-6674 ◽  
Author(s):  
Elias K. Halvas ◽  
Evguenia S. Svarovskaia ◽  
Eric O. Freed ◽  
Vinay K. Pathak
Keyword(s):  
Active Site ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Nucleoside Analogs ◽  
Wild Type ◽  
Reverse Transcriptases ◽  
Ymdd Motif ◽  
High Level ◽  
Hiv 1 ◽  
Murine Leukemia

ABSTRACT The antiretroviral nucleoside analog 2′,3′-dideoxy-3′-thiacytidine (3TC) is a potent inhibitor of wild-type human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). A methionine-to-valine or methionine-to-isoleucine substitution at residue 184 in the HIV-1 YMDD motif, which is located at the RT active site, leads to a high level of resistance to 3TC. We sought to determine whether 3TC can inhibit the replication of wild-type murine leukemia virus (MLV), which contains V223 at the YVDD active site motif of the MLV RT, and of the V223M, V223I, V223A, and V223S mutant RTs. Surprisingly, the wild type and all four of the V223 mutants of MLV RT were highly resistant to 3TC. These results indicate that determinants outside the YVDD motif of MLV RT confer a high level of resistance to 3TC. Therefore, structural differences among similar RTs might result in widely divergent sensitivities to antiretroviral nucleoside analogs.

scholarly journals The LEM Domain Proteins Emerin and LAP2α Are Dispensable for Human Immunodeficiency Virus Type 1 and Murine Leukemia Virus Infections

2008 ◽  
Vol 82 (12) ◽  
pp. 5860-5868 ◽  
Author(s):  
Alok Mulky ◽  
Tatiana V. Cohen ◽  
Serguei V. Kozlov ◽  
Barbara Korbei ◽  
Roland Foisner ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Knockout Mice ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Wild Type ◽  
Immunodeficiency Virus ◽  
Early Replication ◽  
Hiv 1 ◽  
Murine Leukemia

ABSTRACT The human nuclear envelope proteins emerin and lamina-associated polypeptide 2α (LAP2α) have been proposed to aid in the early replication steps of human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MLV). However, whether these factors are essential for HIV-1 or MLV infection has been questioned. Prior studies in which conflicting results were obtained were highly dependent on RNA interference-mediated gene silencing. To shed light on these contradictory results, we examined whether HIV-1 or MLV could infect primary cells from mice deficient for emerin, LAP2α, or both emerin and LAP2α. We observed HIV-1 and MLV infectivity in mouse embryonic fibroblasts (MEFs) from emerin knockout, LAP2α knockout, or emerin and LAP2α double knockout mice to be comparable in infectivity to wild-type littermate-derived MEFs, indicating that both emerin and LAP2α were dispensable for HIV-1 and MLV infection of dividing, primary mouse cells. Because emerin has been suggested to be important for infection of human macrophages by HIV-1, we also examined HIV-1 transduction of macrophages from wild-type mice or knockout mice, but again we did not observe a difference in susceptibility. These findings prompted us to reexamine the role of human emerin in supporting HIV-1 and MLV infection. Notably, both viruses efficiently infected human cells expressing high levels of dominant-negative emerin. We thus conclude that emerin and LAP2α are not required for the early replication of HIV-1 and MLV in mouse or human cells.

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