The Functions and Inhibition of the Membrane Glycoproteins of Paramyxoviruses and Myxoviruses and the Role of the Measles Virus M Protein in Subacute Sclerosing Panencephalitis

The F glycoprotein of paramyxoviruses is responsible for cell fusion and hemolysis and for virus penetration via fusion of viral and cell membranes. These functions are activated by specific proteolytic cleavage of an inactive precursor (Fo) into two disulfide- linked polypeptides (F, and F₂). The susceptibility of the F₀protein to cleavage by a host protease is a major determinant of virus host range and virulence. Synthetic oligopeptides that mimic the N-terminal region of the F, polypeptide are specific inhibitors of paramyxoviruses, and oligopeptides that mimic the N-terminus of the HA₂polypeptide of influenza virus, also generated by cleavage, specifically inhibit that virus. Antibodies to F protein prevent the spread of paramyxovirus infection via membrane fusion, but antibodies to HN protein do not, although they neutralize released virus. These results and previous findings that formalin-treated virus does not induce antibodies to F protein provide an explanation for atypical measles. The HN protein has both receptor-binding and neuraminidase activities, and Cl" inhibition of neuraminidase may modulate these antagonistic activities. Studies in patients with subacute sclerosing panencephalitis (SSPE) suggest that there is a host restriction of synthesis of the M protein of measles virus in brain cells which is involved in the abortive, persistent infection that causes SSPE.