Palmitoylation of the Murine Leukemia Virus Envelope Protein Is Critical for Lipid Raft Association and Surface Expression

Abstract

To investigate the association of the murine leukemia virus (MuLV) Env protein with lipid rafts, we compared wild-type and palmitoylation-deficient mutant Env proteins by using extraction with the mild detergent Triton X-100 (TX-100) followed by a sucrose gradient flotation assay. We found that the wild-type MuLV Env protein was resistant to ice-cold TX-100 treatment and floated to the top of the gradients. In contrast, we observed that the palmitoylation-deficient mutant Env protein was mostly soluble when extracted by ice-cold TX-100 and stayed at the bottom of the gradients. Both the wild-type and mutant Env proteins were found to be soluble when treated with methyl-␤-cyclodextrin before extraction with ice-cold TX-100 or when treated with ice-cold octyl-␤-glucoside instead of TX-100. These results indicate that the MuLV Env protein is associated with lipid rafts and that palmitoylation of the Env protein is critical for lipid raft association. Although the palmitoylation-deficient Env mutant was synthesized at a level similar to that of the wild-type Env, it was found to be expressed at reduced levels on the cell surface. We observed syncytium formation activity with both the wild-type and mutant Env proteins, indicating that palmitoylation or raft association is not required for MuLV viral fusion activity.

Acylation-Mediated Membrane Anchoring of Avian Influenza Virus Hemagglutinin Is Essential for Fusion Pore Formation and Virus Infectivity

“…Such differences have been observed, for instance, between influenza viruses and retroviruses. When acylation of the envelope glycoproteins of retroviruses was abolished, surface transport and incorporation into virions were reduced with a concomitant loss in infectivity (21,34,39). On the other hand, there is no evidence that acylation affects the fusion property of the retrovirus envelope glycoprotein, again in contrast to the case for influenza virus HAs of subtypes H1, H2, and H7.…”

“…In particular, quite a comprehensive picture on the contribution of DIG domains to the biology of retroviruses has evolved in recent years. It was shown that covalently bound lipids promote the association of the viral Gag and envelope proteins with DIG domains of the plasma membrane (21,39) and that this association plays a critical role not only for the assembly and release of virus particles (23,32,37), but also for virus entry into the host cell (10).…”

Murine leukemia virus glycosylated Gag (gPr80 gag ) facilitates interferon-sensitive virus release through lipid rafts

“…We next tested whether gPr80 gag might facilitate M-MuLV release through cholesterol-rich plasma membrane subdomains, also called lipid rafts. HIV buds through lipid rafts (18,19), and this process has also been reported for MuLV (20,21). BST-2 localizes in lipid rafts (22), so IFN induction of BST-2 would be expected to efficiently inhibit release of virions budding through lipid rafts, whereas it would be expected to have less effect on virus released independent of lipid rafts.…”

Wild-Type-Like Viral Replication Potential of Human Immunodeficiency Virus Type 1 Envelope Mutants Lacking Palmitoylation Signals

“…For instance, palmitoylation-deficient Env mutants of murine leukemia virus (MLV) are mostly soluble when extracted using ice-cold Triton X-100, and they stay at the bottom of the sucrose gradient (28). In addition, treatment of cells with ␤-methyl cyclodextrin abolishes the ability of the MLV Env to associate with lipid rafts (28).…”