Reversible inactivation and reactivation of vaccinia virus by manipulation of viral lipid composition.

The role of phospholipids in vaccinia virus was investigated by substituting viral lipids with specific phospholipids. Treatment of virus with sodium dodecyl sulfate, sodium deoxycholate, or Nonidet-P40 (NP-40) resulted in almost complete removal of viral lipid and led to inactivation of the virus. The inactivation induced by the former two was irreversible, but NP-40-treated virus was reactivated upon reassociation with phospholipids. Individual phospholipids, including phosphatidylserine (PS), phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, lysolecithin, sphingomyelin, and acyl bis(monoacylglycero)phosphate (ABMP), were tested for ability to reactivate NP-40-treated virus. Reactivation was induced only by PS. The infectivity of virus that had been treated with NP-40 and then with PS was unstable; the reactivated virus was inactivated within a short period. It was also very sensitive to trypsin. Treatment of NP-40-treated virus with mixtures of PS and ABMP yielded virus that was more resistant to spontaneous and trypsin-induced inactivation. Thus, PS appears to be an essential for infectivity and ABMP appears to play a supplementary role for maintenance of infectivity, perhaps by protecting against inactivating factors.