Binding sites on the midgut cell membrane for the synergistic factor of a granulosis virus of the armyworm ( Pseudaletia unipuncta)

Abstract

The midgut membrane fraction from armyworm larvae ( Pseudaletia unipuncta) has specific binding sites for the synergistic factor (SF), a protein in the capsule matrix of a granulosis virus (GV), that enhances the infection of nuclear polyhedrosis viruses (NPVs). The GVs and NPVs are insect baculoviruses. Optimum binding of the SF was obtained after a 30 min incubation of the membrane fraction at pH 6.0. The number of binding sites is 4.20 × 10 −13 mol/50μg membrane protein and the equilibrium dissociation constant is 1.57 × 10 −9 M. Inactivation of the binding sites by trypsin and heat treatment suggests that some portion of the binding site is proteinaceous. Pre-treatment of the midgut membrane fraction with Concanavalin A and castor bean lectin also inhibits specific binding. These results support the hypothesis that the SF acts as a binding molecule for the attachment of enveloped virions of baculoviruses to the cell plasma membrane.