Associate Professor of Physics & Astronomy and
Adjunct Assistant Professor of Biology
B.S. Sharif University of Technology, Iran
Ph.D. Washington University, St Louis
Saveez Saffarian's Lab Page
Saveez Saffarian's PubMed Literature Search
Biological Chemistry Program
Enveloped Virus Budding
Human immunodeficiency virus is an enveloped lentivirus with a dimeric single-stranded positive sense RNA genome. Budding of the mature virus from the plasma membrane of mammalian cells depends on a combination of Gag polymerization on the cytoplasmic side of the membrane, RNA capture, and contributions from cellular proteins. The cellular machinery normally involved in cytokinesis and multi-vesicular body formation, known as the ESCRT complex, is hijacked by the virus during HIV budding. For the virus to be infectious it needs to incorporate the appropriate genome (two pieces of single stranded RNA), necessary envelope glycoproteins (ENV), and the requisite genome enzymes (reverse transcriptase, protease and ...) in the form of Gag-Pol, while budding from the plasma membrane of cells. We are interested in exploring the detailed mechanisms by which the infectious virions manage to balance these interactions and capture all of their essential components while budding from live cells.
Specifically, we want to know how the viral proteins are organized on the membrane before the initiation of budding; when the correct enzymes essential for later infectivity incorporate into the virion; how the virion avoids incorporating cellular proteins that would restrict its release; and how the cellular machinery hijacked from the cytoplasm assembles at the right time and functions at the budding site.
In our lab we use a combined virological and biophysical approach in which: live infectious viruses are produced and their subsequent budding from live cells is visualized using single molecule and live cell fluorescence imaging approaches. Many of these methodologies have been previously tested in live cells with different biological processes (see references). HIV virions in our studies are non-infectious. In cases where we deem it beneficial to study fully infectious virions, experiments will be done substituting fully infectious Vesicular Stomatitis Virus (VSV) for HIV. VSV is also an enveloped virus and is a member of the Rhabdovirus family, with a single-stranded negative sense RNA genome that like HIV buds through the plasma membrane. VSV was chosen based on its relative biosafety, its robust growth in cell culture, its ease of genetic manipulation, and the availability of well-characterized mutants.
Our lab is physically located at the lower campus, with our microscope in the Department of Physics and our wet benches in the Department of Biology.
Artistic rendering of Vesicular Stomatitis Virus during RNA capture at the plasma membrane. For simplicity only the N molecule is shown. The illustrated packing within the virion is consistent with Cryo EM studies of VSV. The extended spiral outside the formed virion is an artistic expression. It is not clear for how long the RNA would retain its spiral twist in the cytoplasm.
- Cureton DK, Massol RH, et al. (2009) Vesicular Stomatitis Virus Enters Cells through Vesicles Incompletely Coated with Clathrin That Depend upon Actin for Internalization. PLoS Pathog 5(4):e1000394
- Saffarian S, Cocucci E, et al. (2009) Distinct Dynamics of Endocytic Clathrin-Coated Pits and Coated Plaques. PLoS Biol 7(9):e1000191
- Saffarian S, Kirchhausen T (2008) Differential evanescence nanometry: Live-cell fluorescence measurements with 10-nm axial resolution on the plasma membrane. Biophysical Journal 94(6):2333-2342
- Saffarian S, Li Y, et al. (2007) Oligomerization of the EGF Receptor Investigated by Live Cell Fluorescence Intensity Distribution Analysis. Biophys. J 93(3):1021-1031
- Saffarian S, Collier IE, et al. (2004) Interstitial Collagenase Is a Brownian Ratchet Driven by Proteolysis of Collagen. Science 306(5693):108-111