NMR and biochemical studies

RNA‐containing vesicles, recovered from the supernatant of high‐density cell samples of human colon carcinoma, produce a high‐resolution 1H NMR spectrum of lipids characterized by isotropic tumbling; these vesicles contain large amounts of triglycerides and cholesterol esters. Both findings have strict analogies to what is displayed by the proteolipid complexes isolated from the sera of tumor‐bearing patients [(1985) Proc. Natl. Acad. Sci. USA 82, 3455–3459; (1986) FEBS Lett. 203, 164–168]. Lipid analysis and enzymatic tests indicate that these vesicles are selected micromaps of plasma membranes, analogous to those that can be recovered from culture media in which tumor cells are grown [(1985) Dev. Biol. 3, 33–57]. Peculiar lipids, an acylated oligopeptide and a modified phospholipid, are also present in the vesicles

Envelope Lipid-packing as a Critical Factor for the Biological Activity and Stability of Alphavirus Particles Isolated from Mammalian and Mosquito Cells*

Alphaviruses are enveloped arboviruses. The viral envelope is derived from the host cell and is positioned between two icosahedral protein shells (T = 4). Because the viral envelope contains glycoproteins involved in cell recognition and entry, the integrity of the envelope is critical for the success of the early events of infection. Differing levels of cholesterol in different hosts leads to the production of alphaviruses with distinct levels of this sterol loaded in the envelope. Using Mayaro virus, a New World alphavirus, we investigated the role of cholesterol on the envelope of alphavirus particles assembled in either mammalian or mosquito cells. Our results show that although quite different in their cholesterol content, Mayaro virus particles obtained from both cells share a similar high level of lateral organization in their envelopes. This organization, as well as viral stability and infectivity, is severely compromised when cholesterol is depleted from the envelope of virus particles isolated from mammalian cells, but virus particles isolated from mosquito cells are relatively unaffected by cholesterol depletion. We suggest that it is not cholesterol itself, but rather the organization of the viral envelope, that is critical for the biological activity of alphaviruses