CELL ENTRY BY MEASLES-VIRUS - LONG HYBRID RECEPTORS UNCOUPLE BINDING FROM MEMBRANE-FUSION

The pH-independent fusion of membranes induced by measles virus (MV) r equires, in addition to the fusion-competent protein F, hemagglutinin (H), and on the target membrane, the virus receptor CD46. We construct ed hybrid receptors composed of different numbers and combinations of the four CD46 short consensus repeat (SCR) domains, followed by immuno globulin-like domains of another cell surface protein, CD4. Hybrid pro teins containing SCRs I and II bound MV particles and conferred fusion competence to rodent cells, SCRs III and/or TV strengthened MV bindin g, Increasing the distance between the MV binding site and the transme mbrane domain enhanced virus binding but reduced fusion efficiency, A hybrid protein predicted to be about 120 Angstrom (12 nm) longer than the standard receptor lost fusion support function and was dominant ne gative over a functional receptor, These data indicate that receptor p rotein length influences virus binding and determines fusion efficienc y.