This is a spike protein on the virion surface. The brown disc is a lipid membrane envelope.
The spike protein is composed of the three identical chains : chain A, B and C.
Each chain has 1273 amino acids. For the amino acid sequence of the spike protein, see the page
"20 amino acids in a protein".
The receptor binding domain (RBD) touches and recognize human cells.
After binding of the RBD to the human receptor, the spike protein is cleavaged into the head region "S1" and the stem region "S2".
Surface
Surface S1
Surface S2
ribbons
Lipid membrane envelope
chain A
chain B
chain C