Different forms of HSV-1 VP22a within purified virion and infected cells

Utilizing the monoclonal antibody MCA406, our experimental data suggest that the herpes simplex virus type 1 (HSV-1) protein, VP22a, is present in the purified virus in a different form from that present within infected cells, namely the virion and infected-cell form, respectively. It seems reasonable to suggest that two different forms of VP22a are synthesized during the HSV-1 productive cycle. Using varying quantities of reducing agents, both inter- and intramolecular disulfide linkages were demonstrated in this protein family. Moreover, the VP22a-virion form could not be detected under nonreducing conditions by monoclonal antibody, even in the presence of proteolysis inhibitors, i.e. aprotinin, phenyl-methane-sulfonyl fluoride (PMSF) and soybean trypsin inhibitor. Varying temperature had little effect on the breakdown of VP22a disulfide bonds. A higher molecular-weight band, present in the nonreduced gel tracks, clearly indicates the presence of intermolecular disulfide bonds. Similarly, the appearance of bands of lower apparent molecular weight in the nonreduced tracks suggests the presence of intramolecular disulfide bonding. The VP22a infected-cell form may be modified to the virion form during the capsid-assembly process, prior to full capsid formation.