| During the process of budding, the human immunodeficiency virus type 1 (HIV-1) acquires host membrane lipid and protein molecules. The incorporated proteins do not correspond to the host cell surface phenotype. CD45 is specifically excluded from the viral envelope, but is highly expressed on T cells. Conversely, GPI-linked proteins are enriched on virion surfaces. Lipids also have different profiles between virions and cells. Cholesterol and sphingolipids appear to be enriched on virions compared to the cell plasma membrane. Recent studies have shown the existence of microdomains called lipid rafts on cell surfaces that are enriched in cholesterol, sphingolipids, GPI-linked proteins, and signaling proteins. These domains also exclude many transmembrane molecules including CD45. This thesis provides evidence for the budding of HIV-1 selectively from lipid rafts to account for the lipids and proteins incorporated into virions. The significant roles of lipid rafts in HIV-1 biology are discussed. We also examined the effects of a channel-forming bacterial toxin, aerolysin, on HIV-1. Aerolysin targets GPI-linked proteins on cell surfaces, forms heptamers, then inserts as a pore-bearing complex into the cell membrane, exerting its toxic effects. We hypothesized that GPI-anchor proteins on virus would allow binding of aerolysin and affect the infectivity of the virus. We found that HIV-1 was completely neutralized by aerolysin in a GPI-anchor protein-specific manner, such that viruses without GPI-anchored proteins were not susceptible to neutralization by aerolysin. We also found that oligomerization and insertion was essential for neutralization as well. These findings provide insight into virus budding, how budding may contribute to infection, and the role of lipid rafts in the HIV-1 life cycle. |
