Conformational Changes in Sindbis Virus E1 Glycoprotein Induced by Monoclonal Antibody Binding

Abstract

A monoclonal antibody (30.2) raised against Sindbis virus is able to precipitate both E1 and PE2 from [35S]methionine-labeled infected [hamster kidney BHK] cells solubilized with non-ionic detergent. Addition of sodium dodecyl sulfate to the lysate abolishes the precipitation of PE2 without affecting that of E1, thus demonstrating that the antibody is specific for E1. Other Sindbis E1-specific monoclonal antibodies (30.11 and 30.12) precipitate only E1, even from lysates containing only non-ionic detergent, and their presence in such a lysate prevents precipitation of PE2 by antibody 30.2. Apparently, E1-PE2 complexes stable in the presence of non-ionic detergent can be precipitated as such by 1 antibody, but binding of the other antibodies induces dissociation of E1 and PE2. Competition experiments using 125I-labeled antibodies indicate that all 3 antibodies bind to distinct antigenic sites on the E1 molecule. Antibodies 30.11 and 30.12 stimulate each other''s binding in such experiments, which suggests that binding of either of these antibodies alters the conformation of E1 in such a way as to increase its affinity for the other, and at the same time to release PE2. Antibody 30.2 also enhances binding of the other 2 antibodies, but this stimulation is only weakly reciprocated.