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Types of Lipids Present in Viral Envelope

It is generally accepted that the lipids in virus envelopes are derived from the host cell. This is shown by the facts that:

(i) viruses rarely have lipids not found in host cells,
(ii) when viruses are grown in different host cells, they show differences in their lipid patterns, and
(iii) radioactively labelled cellular lipids are incorporated into virions.

The lipids of viruses budded from preformed cellular membranes are early of host cell origin.

In viruses assembled with out continuity with host cell membranes, the evidence of cellular is not so clear cut. In the vaccinia viruses lipid biosynthesis in infected host cells is not basically altered. The virus does not have any unusual or novel lipids. Unusual lipids are, however, found in some viruses.

(a) Phospolipids

e.g. sphingomyelin, phosphatidyl choline phosphatidyl ethanolamine, phosphatidyl serine and phosphatidyl inositol. Of these the former three are predominant, and the other two are usually present in smaller amounts.

(b) Cholesterol

It is significantly higher than in the host cell. The molar ratio cholesterol: phospholipid is about I in viral envelopes and 0.2 in host cells.

(c) Fatty acids

The phospholipids consist predominantly of saturated and unsaturated acids, with chain lengths of 16, 18 and 20 C atoms. Virus fatty acids contain higher amounts of saturated fatty acids than whole cells.