Enveloped viruses enter cells either by fusing their envelope directly to a host cell membrane or by fusing to endSSSmal membrane after being internalized. Fusion in the first entry pathway is triggered by binding to cognate receptor(s), whereas fusion in endocytotic pathway is initiated by low pH within the endosome. Strong evidence exist that the Env glycoprotein of the retrovirus, avian sarcoma and teukosis virus (ASLV), uses both receptor binding and low pH to enter the cell: it undergoes initiaI conformational changes at the plasma membrane as a result of receptor binding, and, after endocytosis, undergoes final changes induced by low pH within endosomes. The unprecedented utilization of this dual triggering mechanism allows the sequential refolding of the ASLV Env that leads to fusion to be better delineated than possible for other viruses. The low pH-requirement for fusion between cells expressing ASLV Env and cognate receptor-expressing cells has been unambiguously demonstrated, but the requirement for low pH during virus entry is still controversial. The pH- dependence of virus-cell and virus-liposome fusion will be rigorously investigated, using lipid and content mixing assays. The identity of the pH-sensitive steps of ASLV Env-induced fusion will be determined by arresting sequential stages of fusion and testing whether low pH is required to proceed to the subsequent stage. For many unrelated viral proteins, a common structural motif referred to as a six-helix bundle, has emerged; there is compelling evidence that this structure is critical for fusion. The sequence homology between ASLV Env and other fusion proteins with known structures, strongly indicates its propensity to form a six-helix bundle. Whether ASLV Env does fold into a bundle to promote fusion will be tested by determining if Env-derived synthetic peptides abolish cell-cell fusion, as was the case for other viral proteins that fold into bundles. Delineating the mechanism of ASLV Env- induced fusion will provide insight into the basic principles by which important human pathogens, such as HIV, Ebola, and flu viruses enter cells and could therefore suggest new antiviral strategies against viral pathogens.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI053668-06
Application #
7176092
Study Section
Experimental Virology Study Section (EVR)
Program Officer
Park, Eun-Chung
Project Start
2003-09-15
Project End
2007-12-31
Budget Start
2007-01-01
Budget End
2007-12-31
Support Year
6
Fiscal Year
2007
Total Cost
$357,054
Indirect Cost
Name
University of MD Biotechnology Institute
Department
Type
Organized Research Units
DUNS #
603819210
City
Baltimore
State
MD
Country
United States
Zip Code
21202
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Hampton, Cheri M; Strauss, Joshua D; Ke, Zunlong et al. (2017) Correlated fluorescence microscopy and cryo-electron tomography of virus-infected or transfected mammalian cells. Nat Protoc 12:150-167
Oum, Yoon Hyeun; Desai, Tanay M; Marin, Mariana et al. (2016) Click labeling of unnatural sugars metabolically incorporated into viral envelope glycoproteins enables visualization of single particle fusion. J Virol Methods 233:62-71
Markosyan, Ruben M; Miao, Chunhui; Zheng, Yi-Min et al. (2016) Induction of Cell-Cell Fusion by Ebola Virus Glycoprotein: Low pH Is Not a Trigger. PLoS Pathog 12:e1005373
Padilla-Parra, Sergi; Marin, Mariana; Kondo, Naoyuki et al. (2014) Pinpointing retrovirus entry sites in cells expressing alternatively spliced receptor isoforms by single virus imaging. Retrovirology 11:47
Matos, Pedro M; Marin, Mariana; Ahn, Byungwook et al. (2013) Anionic lipids are required for vesicular stomatitis virus G protein-mediated single particle fusion with supported lipid bilayers. J Biol Chem 288:12416-25
Padilla-Parra, Sergi; Marin, Mariana; Gahlaut, Nivriti et al. (2013) Fusion of mature HIV-1 particles leads to complete release of a gag-GFP-based content marker and raises the intraviral pH. PLoS One 8:e71002
Padilla-Parra, Sergi; Matos, Pedro M; Kondo, Naoyuki et al. (2012) Quantitative imaging of endosome acidification and single retrovirus fusion with distinct pools of early endosomes. Proc Natl Acad Sci U S A 109:17627-32
Padilla-Parra, Sergi; Marin, Mariana; Kondo, Naoyuki et al. (2012) Synchronized retrovirus fusion in cells expressing alternative receptor isoforms releases the viral core into distinct sub-cellular compartments. PLoS Pathog 8:e1002694

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