Transmembrane phospholipid motions induced by F glycoprotein in hemagglutinating virus of Japan

Abstract

Transfer of phospholipid from the envelope of hemagglutinating virus of Japan (HVJ) to erythrocyte (RBC) membrane [chicken and human] and the virus-induced transfer of phospholipid between RBC membranes were studied using spin-labeled phosphatidylcholine (PC*). The transfer of PC* from membranes labeled densely with PC* to unlabeled membranes was followed by the peak height increase in the ESR spectrum. The 2 kinds of transfer reactions occurred rapidly, as reported previously. To obtain further details, the transfer reactions were studied in HVJ, HVJ inactivated by trypsin, HVJ harvested early, HVJ grown in [chicken embryo] fibroblast cells, the fibroblast HVJ activated by trypsin, influenza virus and glutaraldehyde-treated RBC. The viral F glycoprotein played a crucial role in the transmembrane phospholipid movements and in the fusion and hemolysis of RBC. The transfer from HVJ to RBC occurred partially through an exchange mechanism not accompanying the envelope fusion. This was shown by a decrease in the exchange broadening of the ESR spectrum of released spin-labeled HVJ (HVJ*) and by an increase in the ratio of PC* to viral proteins incorporated into RBC membranes. HVJ modified RBC membrane so as to be able to exchange its phospholipids with those of inactive membranes such as fibroblast HVJ, influenza virus, glutaraldehyde-treated RBC and phosphatidylcholine vesicles. HVJ affected the fluidity of RBC membranes markedly, the environments around PC* being much fluidized. The virus-induced fusion was discussed based on close apposition of the membranes by HANA [hemagglutinin neuraminidase] proteins and on the destabilization and fluidization of RBC membranes by F glycoproteins.