FIG. 1.

Schematic structure and step 1 conformational change of MHV-2 S protein induced by receptor binding. (A) The S protein has an N-terminal signal peptide (SP), a receptor-binding domain (RBD), a fusion peptide (FP), two heptad repeats (HR-N and HR-C), a transmembrane domain (TMD), and a cytoplasmic tail (CT). The putative cleavage site in the central region is identified by a white arrow. Epitopes recognized by the two antibodies (MAb 10G and anti-S2A) are depicted. (B) MHV-2 virions were incubated with various concentrations of soMHVR at 37°C for 30 min. The samples were boiled (lanes 1, 2, 8, and 10) or left unboiled (lanes 3 to 7 and lanes 10 to 14) and analyzed by Western blotting with the indicated antibody. (C) Precleaved and uncleaved S proteins of MHV-JHM-srr7 and MHV-2 were incubated in the presence or absence of soMHVR to compare the trimer formation. The samples were analyzed by native PAGE and Western blotting with the indicated antibody.