Distinct Roles for Sialoside and Protein Receptors in Coronavirus Infection

Qing, Enya; Hantak, Michael; Perlman, Stanley; Gallagher, Tom

We found that JHM-CoV binding to cells depended on host sialic acids. This binding accounted for initial virus attachment to cells, which facilitated subsequent virus engagement with proteinaceous CEACAM receptors. Later in the infection cycle, JHM-CoV spikes facilitated cell fusions and further virus dissemination in a sialic acid-dependent manner. MERS-CoV spike proteins could similarly fuse cells together without requiring prototype protein (hDPP4) receptors, presumably by utilizing sialoside receptors to engage neighboring cells. These findings, summarized in Fig. 7 , suggest that CoV-cell entry and intercellular spread involve the lectin-like activities of spike proteins during both virus-cell attachment and infected-cell expansion into syncytia. green), A59 S1A (PDB accession no. 3JCL, magenta), and MERS S1A (PDB accession no. 5X4R, yellow) using PyMol. MERS S1A residue N222 (stick representation) is located proximally to B-CoV S1A residue E170. (C) MERS VLP binding characterization. MERS-VLPs with equivalent Rluc activities (right) were processed for Western blotting to image S-protein abundance and integrity (left). (D) VLPs were added at equivalent Rluc input multiplicities to human Calu3 or murine LET-1 cells. After 2 h at 4°C, cellassociated Rluc activities were quantified, and data were presented after subtracting background ("No S") Rluc ϩ VLP levels. (E) Effector cells expressing the indicated S proteins were cocultured with target cells expressing hTMPRSS2 and/or hDPP4. (F) MERS S-expressing effector cells were mixed with hTMPRSS2expressing target cells, in the presence of the indicated Fc proteins. All Fc proteins were at 10 M concentration throughout the coculture period. Experimental procedures, data acquisition, and processing were performed as described in the Fig. 1 legend.