scholarly journals Function of the cytoplasmic domain of a retroviral transmembrane protein: p15E-p2E cleavage activates the membrane fusion capability of the murine leukemia virus Env protein.

1994 ◽  
Vol 68 (3) ◽  
pp. 1773-1781 ◽  
Author(s):  
A Rein ◽  
J Mirro ◽  
J G Haynes ◽  
S M Ernst ◽  
K Nagashima
Keyword(s):  
Membrane Fusion ◽  
Murine Leukemia Virus ◽  
Transmembrane Protein ◽  
Leukemia Virus ◽  
Cytoplasmic Domain ◽  
Env Protein ◽  
Protein P15e ◽  
Murine Leukemia

scholarly journals An Aromatic Side Chain Is Required at Residue 8 of SU for Fusion of Ecotropic Murine Leukemia Virus

2004 ◽  
Vol 78 (1) ◽  
pp. 508-512 ◽  
Author(s):  
Zhaohui Qian ◽  
Lorraine M. Albritton
Keyword(s):  
Membrane Fusion ◽  
Aromatic Ring ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Surface Glycoprotein ◽  
Side Chain ◽  
Complete Fusion ◽  
Aromatic Side Chain ◽  
Fusion Pores ◽  
Murine Leukemia

ABSTRACT The surface glycoprotein (SU) of most gammaretroviruses contains a conserved histidine at its amino terminus. In ecotropic murine leukemia virus SU, replacement of histidine 8 with arginine (H8R) or deletion of H8 (H8del) abolishes infection and cell-cell fusion but has no effect on binding to the cellular receptor. We report here that an aromatic ring side chain is essential to the function of residue 8. The size of the aromatic ring appears to be important, as does its ability to form a hydrogen bond. In addition, infection by all of the nonaromatic amino acid substitutions could be partially rescued by the addition of two suppressor mutations (glutamine 227 to arginine [Q227R] and aspartate 243 to tyrosine [D243Y]) or by exposure to chlorpromazine, an agent that induces fusion pores in hemifusion intermediates to complete fusion, suggesting that, like the previously described H8R mutant, the mutants reported here also arrest membrane fusion at the hemifusion state. We propose that H8 is a key switch-point residue in the conformation changes that lead to membrane fusion and present a possible mechanism for how its substitution arrests fusion at the hemifusion state.

scholarly journals R-Peptide Cleavage Potentiates Fusion-Controlling Isomerization of the Intersubunit Disulfide in Moloney Murine Leukemia Virus Env

2007 ◽  
Vol 82 (5) ◽  
pp. 2594-2597 ◽  
Author(s):  
Robin Löving ◽  
Kejun Li ◽  
Michael Wallin ◽  
Mathilda Sjöberg ◽  
Henrik Garoff
Keyword(s):  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Moloney Murine Leukemia Virus ◽  
Isomerization Reaction ◽  
Peptide Cleavage ◽  
In Vivo Assays ◽  
Env Protein ◽  
Murine Leukemia

ABSTRACT Fusion of the membrane of the Moloney murine leukemia virus (Mo-MLV) Env protein is facilitated by cleavage of the R peptide from the cytoplasmic tail of its TM subunit, but the mechanism for this effect has remained obscure. The fusion is also controlled by the isomerization of the intersubunit disulfide of the Env SU-TM complex. In the present study, we used several R-peptide-cleavage-inhibited virus mutants to show that the R peptide suppresses the isomerization reaction in both in vitro and in vivo assays. Thus, the R peptide affects early steps in the activation pathway of murine leukemia virus Env.

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 Threshold Number of Provirus Copies Required per Cell for Efficient Virus Production and Interference in Moloney Murine Leukemia Virus-Infected NIH 3T3 Cells

1998 ◽  
Vol 72 (7) ◽  
pp. 5414-5424 ◽  
Author(s):  
Takashi Odawara ◽  
Masamichi Oshima ◽  
Kent Doi ◽  
Aikichi Iwamoto ◽  
Hiroshi Yoshikura
Keyword(s):  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Natural Infection ◽  
Mrna Level ◽  
Virus Production ◽  
Threshold Level ◽  
Moloney Murine Leukemia Virus ◽  
Sigmoid Curve ◽  
Env Protein ◽  
Murine Leukemia

ABSTRACT The gag-pol readthrough mutant of Moloney murine leukemia virus, MLV-B(CAG) (T. Odawara, H. Yoshikura, M. Oshima, T. Tanaka, D. S. Jones, F. Nemoto, Y. Kuchino, and A. Iwamoto, J. Virol. 65:6376–6379, 1991), was poorly complemented by a mutant encoding only Gag. This is because with all the genetic elements necessary for env expression present in MLV-B(CAG), insufficient Env protein was produced by the cells expressing MLV-B(CAG) for efficient virus production. Since the envmRNA expression per provirus in the MLV-B(CAG)- and wild-type-MLV-producing cells were the same and since the cells expressing the former contained eightfold fewer proviral copies, the insufficient Env expression by the former was found to be due to insufficient proviral copies in the cells. Examination of the cell clones having various proviral copies of Δwt MLV (M. Oshima, T. Odawara, T. Matano, H. Sakahira, Y. Kuchino, A. Iwamoto, and H. Yoshikura, J. Virol. 70:2286–2295, 1996) showed that mRNA level was proportional to the number of proviral copies while interference and virus production followed a sigmoid curve with a sharp rise at the threshold number of proviral copies of around four per cell. Multicycle infection probably continues until the threshold level of proviral copies is attained in natural infection too.

scholarly journals Murine leukemia virus transmembrane protein R-peptide is found in small virus core-like complexes in cells

2006 ◽  
Vol 87 (6) ◽  
pp. 1583-1588 ◽  
Author(s):  
Klaus Bahl Andersen ◽  
Huong Ai Diep ◽  
Anne Zedeler
Keyword(s):  
Cell Membrane ◽  
Murine Leukemia Virus ◽  
Transmembrane Protein ◽  
Leukemia Virus ◽  
Envelope Proteins ◽  
Viral Envelope ◽  
Virus Core ◽  
Small Virus ◽  
Murine Leukemia ◽  
In Cells

The core of the retrovirus Murine leukemia virus (MLV) consists of the Gag precursor protein and viral RNA. It assembles at the cytoplasmic face of the cell membrane where, by an unclear mechanism, it collects viral envelope proteins embedded in the cell membrane and buds off. The C-terminal half of the short cytoplasmic tail of the envelope transmembrane protein (TM) is cleaved off to yield R-peptide and fusion-active TM. In Moloney MLV particles, R-peptide was found to bind to core particles. In cells, R-peptide and low amounts of uncleaved TM were found to be associated with small core-like complexes, i.e. mild detergent-insoluble, Gag-containing complexes with a density of 1.23 g ml−1 and a size of 150–200 S. Our results suggest that TM associates with the assembling core particle through the R-peptide before budding and that this is the mechanism by which the budding virus acquires the envelope proteins.

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