Mechanism of HIV Release through Lipid Rafts

Hung Fan
University of California, San Diego
Basic Biomedical Sciences

When HIV infects cells, the final step in the infection process is release of virus particles from the surface of the cell.  It has been shown that when HIV is released, it “buds” through particular sub-regions of the cell membrane called lipid rafts (LRs).  While budding of HIV through LRs is well-established, the mechanism by which this occurs is not well understood.  A retrovirus of mice, murine leukemia virus (MuLV) has also been found to bud through LRs.  We have recently discovered that a unique protein encoded by MuLV, glycosylated gag (glyco-gag), directs budding of MuLV particles through lipid rafts.  In addition, MuLV glyco-gag can facilitate release of HIV particles from cells, so these two viruses apparently employ similar mechanisms to direct release through LRs.  Since a specific viral protein (glyco-gag) has been found to direct viral release through LRs for MuLV, this provides an experimental approach to identify cellular proteins that are also involved in the process.  We will employ a technique called tandem affinity purification, in which a purification tag (TAP tag) is engineered onto the MuLV glyco-gag protein.  The TAP-tagged glyco-gag will then be used to purify cellular proteins that bind to glyco-gag, and the proteins will be identified by a technique called tandem mass spectrometry.  Once cellular proteins that bind to MuLV glyco-gag have been identified, we will employ specific tests to determine if they are important in directing MuLV budding through LRs.  Proteins that are important for directing MuLV budding through LRs will then be tested for directing HIV release through LRs.  The mechanisms by which these proteins function to direct HIV release to LRs can then be explored.  These experiments may provide new cellular targets for new classes of antiretroviral compounds.