Asymmetry of the lipid-bilayer of Sindbis virus

The organization of the lipid bilayer of the enveloped Sindbis virus has been studied. In the model membrane which consists only of two virus specific glycoproteins and host derived lipids the latter were radioactively labelled with 14C-palmitic acid by prelabelling their BHK 21 host cell lipids. The purified virus particles were submitted to neuramidase, bromelain and combromelain-neuraminidase treatment. It could be demonstrated that N-acetyl neuraminic acid residue of the total hematoside present in the virion is hydrolyzed by neuraminidase leaving the particles fully intact. Proteolysis of the spikes leads to particle aggregation yet an unchanged hematoside content. This was fully transformed into ceramidelactoside by subsequent neuraminidase treatment. The analyses of the ceramide species present in hematoside of the control particles and ceramidelactoside derived thereof by neuraminidase hydrolysis are in very close agreement. From these experiments it is concluded that all hematoside molecules are organized in the outer half of the bilayer of the envelope.