The presence and cleavage of interpeptide disulfide bonds in viral glycoproteins.

The presence and nature of interpeptide disulfide bonds in HANA (Aemagglutinin and neura-minidase) glycoprotein and F (fusion) glycoprotein of HVJ (Sendai virus) are described. In the case of HANA, subunits of the same or very similar molecular weight were inter connected with a disulfide bond(s). Cleavage of the bond(s) can easily be achieved by the addition of 1 mM dithiothreitol with concomitant loss of the biological activities of the glyco-protein. After splitting of the interconnecting bonds, all the HANA protein subunits remained bound on the viral membrane. To observe the cleavage of the interpeptide disulfide bond between the F and F subunits of F glycoprotein, higher concentrations of sulfhydryl compounds were required than were necessary for HANA protein. Splitting of the disulfide bond under either denaturing or non-denaturing conditions failed to release both segments of F protein from the virion. Therefore, F glycoprotein seems to have at least two membrane binding sites, one on F and the other on F. On the other hand, the disulfide bond which connects the HA and HA subunits of influenza virus is hardly cleaved under non-denaturing conditions. Addition of 8 M urea or 6 M guanidine HCl, which completely inactivates HA activity, was necessary for the splitting of this disulfide bond by thiol compounds. Interestingly, the HA submit was released from the virion after the cleavage. Thus, unlike F and F of HVJ, the HA subunit seems to have no hydrophobic binding site to the membrane. A model for the arrangement of these subunits on the viral membrane is proposed.