Human immunodeficiency virus type 1 Nef protein modulates the lipid composition of virions and host cell membrane microdomains.

BACKGROUND: The Nef protein of Human Immunodeficiency Viruses optimizes viral spread in the infected host by manipulating cellular transport and signal transduction machineries. Nef also boosts the infectivity of HIV particles by an unknown mechanism. Recent studies suggested a correlation between the association of Nef with lipid raft microdomains and its positive effects on virion infectivity. Furthermore, the lipidome analysis of HIV-1 particles revealed a marked enrichment of classical raft lipids and thus identified HIV-1 virions as an example for naturally occurring membrane microdomains. Since Nef modulates the protein composition and function of membrane microdomains we tested here if Nef also has the propensity to alter microdomain lipid composition. RESULTS: Quantitative mass spectrometric lipidome analysis of highly purified HIV-1 particles revealed that the presence of Nef during virus production from T lymphocytes enforced their raft character via a significant reduction of polyunsaturated phosphatidylcholine species and a specific enrichment of sphingomyelin. In contrast, Nef did not significantly affect virion levels of phosphoglycerolipids or cholesterol. The observed alterations in virion lipid composition were insufficient to mediate Nef's effect on particle infectivity and Nef augmented virion infectivity independently of whether virus entry was targeted to or excluded from membrane microdomains. However, altered lipid compositions similar to those observed in virions were also detected in detergent-resistant membrane preparations of virus producing cells. CONCLUSION: Nef alters not only the proteome but also the lipid composition of host cell microdomains. This novel activity represents a previously unrecognized mechanism by which Nef could manipulate HIV-1 target cells to facilitate virus propagation in vivo.

The HIV lipidome: a raft with an unusual composition.

The lipids of enveloped viruses play critical roles in viral morphogenesis and infectivity. They are derived from the host membranes from which virus budding occurs, but the precise lipid composition has not been determined for any virus. Employing mass spectrometry, this study provides a quantitative analysis of the lipid constituents of HIV and a comprehensive comparison with its host membranes. Both a substantial enrichment of the unusual sphingolipid dihydrosphingomyelin and a loss of viral infectivity upon inhibition of sphingolipid biosynthesis in host cells are reported, establishing a critical role for this lipid class in the HIV replication cycle. Intriguingly, the overall lipid composition of native HIV membranes resembles detergent-resistant membrane microdomains and is strikingly different from that of host cell membranes. With this composition, the HIV lipidome provides strong evidence for the existence of lipid rafts in living cells.

The membrane domains occupied by glycosylphosphatidylinositol-anchored prion protein and Thy-1 differ in lipid composition.

Glycosylphosphatidylinositol-anchored prion protein and Thy-1, found in adjacent microdomains or "rafts" on the neuronal surface, traffic very differently and show distinctive differences in their resistance to detergent solubilization. Monovalent immunogold labeling showed that the two proteins were largely clustered in separate domains on the neuronal surface: 86% of prion protein was clustered in domains containing no Thy-1, although 40% of Thy-1 had a few molecules of prion protein associated with it. Only 1% of all clusters contained appreciable levels of both proteins (