Structure and assembly of lipid-containing viruses, with special reference to bacteriophage PM2 as one type of model system

Abstract

The simpler lipid-containing viruses (influenza, Semliki Forest, PM2) may have a phospholipid bilayer sandwiched between an outer shell of protein and an internal nucleocapsid possessing helical or icosahedral symmetry. Extensive physical and chemical studies have enabled us to form a more detailed picture of the structure of bacteriophage PM2 and controlled stepwise degradation of the virion has helped us to localize the four viral proteins. The surface protein (II) of PM2 is basic and interacts with the acidic phosphatidylglycerol of the bilayer to stabilize the membrane. The nucleocapsid protein (III) has proteolipid characteristics and may interact with the phospholipids in a hydrophobic fashion. The spikes are formed from protein I and the fourth protein (IV) is closely associated with the DNA. It is possible to reassemble the virus by reversing the degradation steps. Assembly has been especially useful in revealing the processes whereby the proteins and lipids interact to form the bilayer. Furthermore, results of in vivo studies of phospholipid synthesis and both in vivo and in vitro studies of viral protein synthesis have enabled us to form a reasonably complete picture of the biosynthesis of PM2.

Bacteriophage PM2 Has a Protein Capsid Surrounding a Spherical Proteinaceous Lipid Core

“…The previous structural model proposed that the lipid bilayer is sandwiched between the outer capsid and an inner protein shell composed of one protein species (29,30,31). However, the observation that the number of structural proteins is much higher than previously expected (38) and the results obtained here considerably change the idea of how the inner part of the virion is organized.…”