THE S2 SUBUNIT OF THE MURINE CORONAVIRUS SPIKE PROTEIN IS NOT INVOLVED IN RECEPTOR-BINDING

The receptor-binding capacity of the S2 subunit of the murine coronavirus S protein was examined by testing the inhibition of virus-receptor binding, Sp-4 virus and S1N(330), which consists of the N-terminal 330 amino acids of the S1 protein, both of which exhibited receptor-binding capacity, were able to prevent the binding of cl-2 virus to the receptor, while the mutant protein S1N(330)-159, which failed to bind to the receptor protein, and S2TM(-), which lacks the transmembrane and cytoplasmic: domains normally existing in the S2, were unable to prevent the binding of cl-2. By using cultured DBT cells, it was revealed that the infection of cells by cl-2 virus was significantly inhibited by S1N(330) but not by S2TM(-). These results indicate that the S2 protein is not involved in the receptor binding of murine coronaviruses.