Receptor usage

The S protein  of coronaviruses is a surface-located trimeric glycoprotein consisting of two subunits: the N-terminal S1 subunit and C-terminal S2 subunit. The S1 subunit specializes in recognizing  and binding to the host cell receptor while the S2 region is responsible for membrane fusion. Compared with the S2, the S1 subunit shows much higher variability. Owing to its function of receptor binding, the variation in S protein defines in large part the tissue tropism and host range of different coronaviruses.