Palmitoylation of the HIV-1 envelope glycoprotein is critical for viral infectivity

Recent studies suggest that HIV-I budding occurs selectively from detergent -insoluble membrane domains, referred to as lipid rafts. Palmitoylation is thought to be one of the factors responsible for targeting membrane protein s to lipid rafts. The cytoplasmic domain of the HIV-1 envelope glycoprotein (gp160) contains two palmitoylated cysteine residues. In this work, we stu died the solubility of gp160 after detergent extraction. We show that wild- type gp160 is mostly insoluble after ice-cold Triton X-100 extraction, but that it becomes almost completely soluble at 37 degreesC. In contrast, we f ind that a mutant gp160, in which the two palmitoylated cysteine residues a re replaced by serine, is Triton X-100 soluble even under ice-cold extracti on. These findings are consistent with the properties of proteins that loca lize to lipid rafts and strongly suggest that gp160 is associated with lipi d rafts. Further. removal of both palmitoylation sites results in the forma tion of virus with low levels of gp160 incorporation as well as a decrease in viral infectivity by 60-fold. Our results strongly support the suggestio n that HIV-1 buds from lipid rafts and point to a role for rafts as a viral assembly hub.