Functional differences between the external and protoplasmic surfaces of plasma membranes in activating vaccinia virus infectivity

Abstract

The titer of vaccinia virus strain IHD-J increased when noninfectious protected-form virus was activated to become infectious by incubation with isolated plasma membrane from KB cells. Activation proceeded via two reactions at an optimum pH of 7.4. The first reaction rapidly converted protected-form virus to infectious- and activated-form virus. A heat-stable component of the plasma membrane mediated these changes even in the presence of a protease inhibitor (PMSF). The second reaction, mediated by a heat-labile component of the plasma membrane, changed infectious-form virus to activated-form virus; this reaction was PMSF sensitive. Activation was higher in the first reaction. Bead-bound KB cell plasma membrane catalyzed the first, but had little ability to mediate the second reaction. Although intact mouse RBC lacked activation capacity, its protoplasmic surface activated virus infectivity via the first reaction. The second reaction shared characteristics with activation that takes place during the penetration phase of viral infection. Our observations suggest that a heat-stable and heat-labile component are responsible for the first and second reaction, respectively, and that they function on the protoplasmic side and on the exterior surface of the plasma membrane, respectively.