Abstract
Fusion of Sendai virus envelopes with erythrocyte membranes or with phosphatidylcholine/cholesterol liposomes requires the presence of the two viral glycoproteins, namely the hemagglutinin/neuraminidase (HN) and the fusion (F) polypeptides. Membrane vesicles bearing only the HN or the F glycoprotein (HN or F vesicles) or a mixture of both do not possess fusogenic activity. These results clearly show that in order to be fusogenic, the two viral envelope glycoproteins must be present within the same membrane, thus indicating their mutual interaction. Circular dichroism studies revealed that the conformation of the viral glycoproteins in reconstituted viral envelopes or in HN-F vesicles (vesicles formed by co-reconstitution of the HN and F glycoproteins) is different from that of the conformation of these glycoproteins in either HN or F vesicles or in a mixture of both. It has been observed that the mean residue ellipticity as measured at 222 nm (theta 222) of the viral glycoproteins in reconstituted Sendai virus envelopes (RSVE) is lower by about 75% than the value observed for these glycoproteins in isolated HN or F vesicles. Treatment of RSVE or of HN-F vesicles with inhibitors of the viral fusogenic activity such as phenylmethylsulfonyl fluoride, proteolytic enzymes, or incubation at 70 degrees C caused a substantial conformational change in the viral glycoproteins. The theta 222 of unfusogenic RSVE or unfusogenic HN-F vesicles is very close to that observed for a mixture of HN and F vesicles. It is proposed here that in order to be fusogenic, the viral envelope glycoproteins must possess a certain conformation which exists only when they are present within the same membrane.
Highlights
From the Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
Circular dichroism studies revealed that the conformation of the viral glycoproteins inreconstituted viral envelopesor in HN-F vesilaboratory [4,5] have shown that membrane vesicles containing the viral F glycoprotein failed to fuse with cell plasma membranes even when binding was mediated by other ligands
The results of the present work indicate that a certain and specific conformation is enforced upon the two Sendai viral glycoproteinswhen they are presenwtithin the virus envelope
Summary
With PC/cholesterol liposomes nor induce hemolysis in human erythrocytes (Table I). Virus-induced hemolysis has been. HN-F vesicles (viral envelopesformed by co-reconstitution of HN and F glycoproteins, see “Materials and Methods”) exhibited a high hemolytic activity and were able to fuse with PC/cholesterol liposomes (Table I). These observations raise the possibility that an intermolecular interaction or association between the viral HN and F glycoproteins is necessary. HN- or F-bearing vesicles were obtained after removal of the detergent by SM-2 Bio-Beads, as described earlier [12]. Reconstituted this assumption, CDwas used for the detection of such a putative interaction.
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