English: (left) Schematic diagrams of coronavirus virions; (right top) The topology of the four structural envelope proteins. All proteins are depicted as monomers, but the S and HE proteins form homotrimers and homodimers, respectively. Oligosaccharides are shown on the M, S, and HE proteins. Although a number are omitted, the S and HE proteins contain 21 to 35 and 9 (BCoV HE) potential N-glycosylation sites, respectively; (right bottom) Electron micrograph of SCoV. Bar: 100 nm. (EM image courtesy of Dr. Nagata at National Institute of Infectious Diseases).