scholarly journals Reassessing the Role of Region A in Pit1-Mediated Viral Entry

2002 ◽  
Vol 76 (15) ◽  
pp. 7683-7693 ◽  
Author(s):  
Karen B. Farrell ◽  
Jill L. Russ ◽  
Ravi K. Murthy ◽  
Maribeth V. Eiden
Keyword(s):  
Binding Site ◽  
Viral Entry ◽  
Leukemia Virus ◽  
Viral Envelope ◽  
Feline Leukemia Virus ◽  
Receptor Function ◽  
Viral Envelope Protein ◽  
Virus Binding ◽  
Binding Epitope ◽  
Gibbon Ape Leukemia Virus

ABSTRACT The mammalian gammaretroviruses gibbon ape leukemia virus (GALV) and feline leukemia virus subgroup B (FeLV-B) can use the same receptor, Pit1, to infect human cells. A highly polymorphic nine-residue sequence within Pit1, designated region A, has been proposed as the virus binding site, because mutations in this region abolish Pit1-mediated cellular infection by GALV and FeLV-B. However, a direct correlation between region A mutations deleterious for infection and loss of virus binding has not been established. We report that cells expressing a Pit1 protein harboring mutations in region A that abolish receptor function retain the ability to bind virus, indicating that Pit1 region A is not the virus binding site. Furthermore, we have now identified a second region in Pit1, comprising residues 232 to 260 (region B), that is required for both viral entry and virus binding. Epitope-tagged Pit1 proteins were used to demonstrate that mutations in region B result in improper orientation of Pit1 in the cell membrane. Compensatory mutations in region A can restore proper orientation and full receptor function to these region B mutants. Based on these results, we propose that region A of Pit1 confers competence for viral entry by influencing the topology of the authentic binding site in the membrane and hence its accessibility to a viral envelope protein. Based on glycosylation studies and results obtained by using N- and C-terminal epitope-tagged Pit1, region A and region B mutants, and the transmembrane helices predicted with the PHD PredictProtein algorithm, we propose a new Pit1 topology model.

scholarly journals The YXXL Sequences of a Transmembrane Protein of Bovine Leukemia Virus Are Required for Viral Entry and Incorporation of Viral Envelope Protein into Virions

1999 ◽  
Vol 73 (2) ◽  
pp. 1293-1301 ◽  
Author(s):  
Kazunori Inabe ◽  
Masako Nishizawa ◽  
Shigeru Tajima ◽  
Kazuyoshi Ikuta ◽  
Yoko Aida
Keyword(s):  
Viral Entry ◽  
Envelope Protein ◽  
Bovine Leukemia Virus ◽  
Leukemia Virus ◽  
Transient Transfection ◽  
Viral Envelope ◽  
Tyrosine Residue ◽  
Wild Type ◽  
Viral Envelope Protein

ABSTRACT The cytoplasmic domain of an envelope transmembrane glycoprotein (gp30) of bovine leukemia virus (BLV) has two overlapping copies of the (YXXL)2 motif. The N-terminal motif has been implicated in in vitro signal transduction pathways from the external to the intracellular compartment and is also involved in infection and maintenance of high viral loads in sheep that have been experimentally infected with BLV. To determine the role of YXXL sequences in the replication of BLV in vitro, we changed the tyrosine or leucine residues of the N-terminal motif in an infectious molecular clone of BLV, pBLV-IF, to alanine to produce mutated proviruses designated Y487A, L490A, Y498A, L501A, and Y487/498A. Transient transfection of African green monkey kidney COS-1 cells with proviral DNAs that encoded wild-type and mutant sequences revealed that all of the mutated proviral DNAs synthesized mature envelope proteins and released virus particles into the growth medium. However, serial passages of fetal lamb kidney (FLK) cells, which are sensitive to infection with BLV, after transient transfection revealed that mutation of a second tyrosine residue in the N-terminal motif completely prevented the propagation of the virus. Similarly, Y498A and Y487/498A mutant BLV that was produced by the stably transfected COS-1 cells exhibited significantly reduced levels of cell-free virion-mediated transmission. Analysis of the protein compositions of mutant viruses demonstrated that lower levels of envelope protein were incorporated by two of the mutant virions than by wild-type and other mutant virions. Furthermore, a mutation of a second tyrosine residue decreased the specific binding of BLV particles to FLK cells and the capacity for viral penetration. Our data indicate that the YXXL sequences play critical roles in both viral entry and the incorporation of viral envelope protein into the virion during the life cycle of BLV.

scholarly journals Fusion-Defective Gibbon Ape Leukemia Virus Vectors Can Be Rescued by Homologous but Not Heterologous Soluble Envelope Proteins

2002 ◽  
Vol 76 (9) ◽  
pp. 4267-4274 ◽  
Author(s):  
Karen B. Farrell ◽  
Yuan-Tsang Ting ◽  
Maribeth V. Eiden
Keyword(s):  
Viral Entry ◽  
Culture Medium ◽  
Leukemia Virus ◽  
Envelope Proteins ◽  
Feline Leukemia Virus ◽  
Receptor Binding Domain ◽  
Epitope Tag ◽  
Transporter Protein ◽  
Gibbon Ape Leukemia Virus ◽  
First Time

ABSTRACT Murine leukemia virus (MLV)-derived envelope proteins containing alterations in or adjacent to the highly conserved PHQ motif present at the N terminus of the envelope surface subunit (SU) are incorporated into vector particles but are not infectious due to a postbinding block to viral entry. These mutants can be rendered infectious by the addition of soluble receptor-binding domain (RBD) proteins in the culture medium. The RBD proteins that rescue the infectivity of these defective MLV vectors can be derived from the same MLV or from other MLVs that use distinct receptors to mediate entry. We have now constructed functional immunologically reactive gibbon ape leukemia virus (GALV) envelope proteins, tagged with a feline leukemia virus (FeLV)-derived epitope tag, which are efficiently incorporated into infectious particles. Tagged GALV envelope proteins bind specifically to cells expressing the phosphate transporter protein Pit1, demonstrating for the first time that Pit1 is the binding receptor for GALV and not a coreceptor or another type of GALV entry factor. We have also determined that GALV particles bearing SU proteins with an insertion C-terminal to the PHQ motif (GALV I10) bind Pit1 but fail to infect cells. Incubation with soluble GALV RBD renders GALV I10 particles infectious, whereas incubation with soluble RBDs from MLV or FeLV-B does not. This finding is consistent with the results obtained by Lauring et al. using FeLV-T, a virus that employs Pit1 as a receptor but requires soluble FeLV RBD for entry. MLV and GALV RBDs are not able to render FeLV-T infectious (A. S. Lauring, M. M. Anderson, and J. Overbaugh, J. Virol. 75:8888-8898, 2001). Together, these results suggest that fusion-defective FeLV-T and GALV are restricted to homologous RBD rescue of infectivity.

scholarly journals A 13-Amino-Acid Pit1-Specific Loop 4 Sequence Confers Feline Leukemia Virus Subgroup B Receptor Function upon Pit2

2000 ◽  
Vol 74 (6) ◽  
pp. 2926-2929 ◽  
Author(s):  
Kasper Dreyer ◽  
Finn S. Pedersen ◽  
Lene Pedersen
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Leukemia Virus ◽  
Human Protein ◽  
Feline Leukemia Virus ◽  
Related Protein ◽  
Receptor Function ◽  
Extracellular Loop ◽  
Gibbon Ape Leukemia Virus

ABSTRACT Feline leukemia virus subgroup B (FeLV-B) and gibbon ape leukemia virus (GALV) utilize the human protein Pit1 but not the related protein, Pit2, as receptor. A stretch of 9 amino acids, named region A, was identified in the putative fourth extracellular loop of Pit1 (residues 550 through 558) as critical for FeLV-B and GALV receptor function. However, the presence of Pit1 region A did not confer receptor function for FeLV-B upon Pit2, while it did so for GALV. We have here shown that the presence of two Pit1-specific loop 4 residues (tyrosine 546 and valine 548) in addition to Pit1 region A is sufficient to make Pit2 an efficient FeLV-B receptor; that is, a stretch of 13 amino acids encompassing all loop 4 amino acid differences between Pit1 and Pit2 comprises a C-terminal determinant for FeLV-B receptor function. Thus, the same limited receptor region is sufficient to confer receptor function for both viruses upon Pit2.

scholarly journals Single Amino Acid Insertion in Loop 4 Confers Amphotropic Murine Leukemia Virus Receptor Function upon Murine Pit1

1998 ◽  
Vol 72 (5) ◽  
pp. 4524-4527 ◽  
Author(s):  
Mikkel D. Lundorf ◽  
Finn S. Pedersen ◽  
Bryan O’Hara ◽  
Lene Pedersen
Keyword(s):  
Amino Acid ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Feline Leukemia Virus ◽  
Single Amino Acid ◽  
Receptor Function ◽  
Amphotropic Murine Leukemia Virus ◽  
Gibbon Ape Leukemia Virus ◽  
Murine Leukemia

ABSTRACT Pit1 is the human receptor for gibbon ape leukemia virus (GALV) and feline leukemia virus subgroup B (FeLV-B), while the related human protein Pit2 is a receptor for amphotropic murine leukemia virus (A-MuLV). The A-MuLV-related isolate 10A1 can utilize both Pit1 and Pit2 as receptors. A stretch of amino acids named region A was identified in Pit1 (residues 550 to 558 in loop 4) as critical for GALV and FeLV-B receptor function. We have here investigated the role of region A in A-MuLV and 10A1 entry. Insertion of a single amino acid in region A of mouse Pit1 resulted in a functional A-MuLV receptor, showing that region A plays a role in A-MuLV infection. Moreover, the downregulation of 10A1 receptor function by changes in region A of human Pit1 indicates that this region is also involved in 10A1 entry. Therefore, region A seems to play a role in infection by all viruses utilizing Pit1 and/or Pit2 as receptors.

scholarly journals The Degree of Folding Instability of the Envelope Protein of a Neurovirulent Murine Retrovirus Correlates with the Severity of the Neurological Disease

2009 ◽  
Vol 83 (12) ◽  
pp. 6079-6086 ◽  
Author(s):  
J. L. Portis ◽  
P. Askovich ◽  
J. Austin ◽  
Y. Gutierrez-Cotto ◽  
F. J. McAtee
Keyword(s):  
Neurodegenerative Disease ◽  
Unfolded Protein Response ◽  
Envelope Protein ◽  
Neurological Disease ◽  
Leukemia Virus ◽  
Strong Support ◽  
Viral Envelope ◽  
Viral Envelope Protein ◽  
Unfolded Protein ◽  
Protein Response

ABSTRACT A small group of ecotropic murine retroviruses cause a spongiform neurodegenerative disease manifested by tremor, paralysis, and wasting. The neurovirulence of these viruses has long been known to be determined by the sequence of the viral envelope protein, although the nature of the neurotoxicity remains to be clarified. Studies on the neurovirulent viruses FrCasNC and Moloney murine leukemia virus ts1 indicate that the nascent envelope protein misfolds, is retained in the endoplasmic reticulum (ER), and induces an unfolded protein response. In the present study we constructed a series of viruses with chimeric envelope genes containing segments from virulent and avirulent retroviruses. Each of the viruses studied was highly neuroinvasive but differed in the severity of the neurological disease they induced. Only viruses that contained the receptor-binding domain (RBD) of the neurovirulent virus induced neurological disease. Likewise, only viruses containing the RBD of the neurovirulent virus exhibited increased binding of the ER chaperone BiP to the envelope precursor protein and induced the unfolded protein response. Thus, the RBD determined both neurovirulence and folding instability. Among viruses carrying the neurovirulent RBD, the severity of the disease was increased when envelope sequences from the neurovirulent virus outside the RBD were also present. Interestingly, these sequences appeared to further increase the degree of folding instability (BiP binding) of the viral envelope protein. These results provide strong support for the hypothesis that this spongiform neurodegenerative disease represents a virus-induced protein folding disorder.

scholarly journals Genetic and Biochemical Analyses of Receptor and Cofactor Determinants for T-Cell-Tropic Feline Leukemia Virus Infection

2002 ◽  
Vol 76 (16) ◽  
pp. 8069-8078 ◽  
Author(s):  
Adam S. Lauring ◽  
Heather H. Cheng ◽  
Maribeth V. Eiden ◽  
Julie Overbaugh
Keyword(s):  
T Cell ◽  
Host Cell ◽  
Transmembrane Protein ◽  
Leukemia Virus ◽  
Direct Interaction ◽  
Cell Receptor ◽  
Cellular Protein ◽  
Viral Envelope ◽  
Feline Leukemia Virus ◽  
Cofactor Binding

ABSTRACT Entry by retroviruses is mediated through interactions between the viral envelope glycoprotein and the host cell receptor(s). We recently identified two host cell proteins, FeLIX and Pit1, that are necessary for infection by cytopathic, T-cell-tropic feline leukemia viruses (FeLV-T). Pit1 is a classic multiple transmembrane protein used as a receptor by several other simple retroviruses, including subgroup B FeLV (FeLV-B), and FeLIX is a secreted cellular protein expressed from endogenous FeLV-related sequences (enFeLV). FeLIX is nearly identical to FeLV-B envelope sequences that encode the N-terminal half of the viral surface unit (SU), because these FeLV-B sequences are acquired by recombination with enFeLV. FeLV-B SUs can functionally substitute for FeLIX in mediating FeLV-T infection. Both of these enFeLV-derived cofactors can efficiently facilitate FeLV-T infection only of cells expressing Pit1, not of cells expressing the related transport protein Pit2. We therefore have used chimeric Pit1/Pit2 receptors to map the determinants for cofactor binding and FeLV-T infection. Three distinct determinants appear to be required for cofactor-dependent infection by FeLV-T. We also found that Pit1 sequences within these same domains were required for binding by FeLIX to the Pit receptor. In contrast, these determinants were not all required for receptor binding by the FeLV-B SU cofactors used in this study. These data indicate that cofactor binding is not sufficient for FeLV-T infection and suggest that there may be a direct interaction between FeLV-T and the Pit1 receptor.

scholarly journals A GP64-Null Baculovirus Pseudotyped with Vesicular Stomatitis Virus G Protein

2001 ◽  
Vol 75 (6) ◽  
pp. 2544-2556 ◽  
Author(s):  
J. T. Mangor ◽  
S. A. Monsma ◽  
M. C. Johnson ◽  
G. W. Blissard
Keyword(s):  
G Protein ◽  
Vesicular Stomatitis Virus ◽  
Viral Entry ◽  
Viral Envelope ◽  
Productive Infection ◽  
Pseudotyped Virus ◽  
Sf9 Cells ◽  
Viral Envelope Protein ◽  
Virion Protein ◽  
Vesicular Stomatitis

ABSTRACT The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) GP64 protein is an essential virion protein that is involved in both receptor binding and membrane fusion during viral entry. Genetic studies have shown that GP64-null viruses are unable to move from cell to cell and this results from a defect in the assembly and production of budded virions (BV). To further examine requirements for virion budding, we asked whether a GP64-null baculovirus, vAc64−, could be pseudotyped by introducing a heterologous viral envelope protein (vesicular stomatitis virus G protein [VSV-G]) into its membrane and whether the resulting virus was infectious. To address this question, we generated a stably transfected insect Sf9 cell line (Sf9VSV-G) that inducibly expresses the VSV-G protein upon infection with AcMNPV Sf9VSV-G and Sf9 cells were infected with vAc64−, and cells were monitored for infection and for movement of infection from cell to cell. vAc64− formed plaques on Sf9VSV-G cells but not on Sf9 cells, and plaques formed on Sf9VSV-G cells were observed only after prolonged intervals. Passage and amplification of vAc64− on Sf9VSV-G cells resulted in pseudotyped virus particles that contained the VSV-G protein. Cell-to-cell propagation of vAc64− in the G-expressing cells was delayed in comparison to wild-type (wt) AcMNPV, and growth curves showed that pseudotyped vAc64− was generated at titers of approximately 106 to 107 infectious units (IU)/ml, compared with titers of approximately 108 IU/ml for wt AcMNPV. Propagation and amplification of pseudotyped vAc64− virions in Sf9VSV-G cells suggests that the VSV-G protein may either possess the signals necessary for baculovirus BV assembly and budding at the cell surface or may otherwise facilitate production of infectious baculovirus virions. The functional complementation of GP64-null viruses by VSV-G protein was further demonstrated by identification of a vAc64−-derived virus that had acquired the G gene through recombination with Sf9VSV-G cellular DNA. GP64-null viruses expressing the VSV-G gene were capable of productive infection, replication, and propagation in Sf9 cells.

scholarly journals Virion Background and Efficiency of Virion Incorporation Determine Susceptibility of Simian Immunodeficiency Virus Env-Driven Viral Entry to Inhibition by IFITM Proteins

2016 ◽  
Vol 91 (2) ◽  
Author(s):  
Florian Wrensch ◽  
Markus Hoffmann ◽  
Sabine Gärtner ◽  
Inga Nehlmeier ◽  
Michael Winkler ◽  
...  
Keyword(s):  
Simian Immunodeficiency Virus ◽  
Viral Entry ◽  
Envelope Protein ◽  
Viral Envelope ◽  
Impact Sensitivity ◽  
Published Data ◽  
Viral Envelope Protein ◽  
Virion Incorporation ◽  
Immunodeficiency Virus ◽  
First Time

ABSTRACT Interferon-induced transmembrane proteins (IFITMs) can inhibit the cellular entry of several enveloped viruses, including simian immunodeficiency virus (SIV). The blockade of SIV by IFITMs is isolate specific, raising the question of which parameters impact sensitivity to IFITM. We show that the virion context in which SIV-Env is presented and the efficiency of virion incorporation determine Env susceptibility to inhibition by IFITMs. Thus, determinants other than the nature of the envelope protein can impact the IFITM sensitivity of viral entry. IMPORTANCE The host cell-encoded IFITM proteins can block viral entry and are an important component of the innate defenses against viral infection. However, the determinants controlling whether a virus is susceptible to blockade by IFITM proteins are incompletely understood. Our study shows that the amount of envelope proteins incorporated into virions as well as the nature of the virion particle itself can impact the sensitivity of viral entry to IFITMs. These results show for the first time that determinants other than the viral envelope protein can impact sensitivity to IFITM and have implications for the interpretation of previously published data on inhibition of viruses by IFITM proteins. Moreover, our findings might help to define the mechanism underlying the antiviral activity of IFITM proteins.

scholarly journals Entry of Amphotropic Murine Leukemia Virus Is Influenced by Residues in the Putative Second Extracellular Domain of Its Receptor, Pit2

1998 ◽  
Vol 72 (6) ◽  
pp. 4956-4961 ◽  
Author(s):  
Betsy D. Leverett ◽  
Karen B. Farrell ◽  
Maribeth V. Eiden ◽  
Carolyn A. Wilson
Keyword(s):  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Critical Role ◽  
Functional Characterization ◽  
Extracellular Domain ◽  
Receptor Function ◽  
Amphotropic Murine Leukemia Virus ◽  
Fold Reduction ◽  
Gibbon Ape Leukemia Virus ◽  
Murine Leukemia

ABSTRACT Human cells express distinct but related receptors for the gibbon ape leukemia virus (GALV) and the amphotropic murine leukemia virus (A-MuLV), termed Pit1 and Pit2, respectively. Pit1 is not able to function as a receptor for A-MuLV infection, while Pit2 does not confer susceptibility to GALV. Previous studies of chimeric receptors constructed by interchanging regions of Pit1 and Pit2 failed to clarify the determinants unique to Pit2 which correlate with A-MuLV receptor function. In order to identify which regions of Pit2 are involved in A-MuLV receptor function, we exchanged the putative second and third extracellular domains of Pit1, either individually or together, with the corresponding regions of Pit2. Our functional characterization of these receptors indicates a role for the putative second extracellular domain (domain II) in A-MuLV infection. We further investigated the influence of domain II with respect to A-MuLV receptor function by performing site-specific mutagenesis within this region of Pit2. Many of the mutations had little or no effect on receptor function. However, the substitution of serine for methionine at position 138 (S138M) in a Pit1 chimera containing domain II of Pit2 resulted in a 1,000-fold reduction in A-MuLV receptor function. Additional mutations made within domain II of the nonfunctional S138M mutant restored receptor function to nearly wild-type efficiency. The high degree of tolerance for mutations as well as the compensatory effect of particular substitutions observed within domain II suggests that an element of secondary structure within this region plays a critical role in the interaction of the receptor with A-MuLV.

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