Logos of designed sequences. (a) Sequence composition of the flattened apo CoV-2 state. (b) Sequence composition of the CoV-2 complex, using the flattening biases. Large letters signify residue types encountered in sequences of better affinity for hACE2, relative to the CoV-2 sequence LQSN. All 20 natural amino acids except P and G were considered at the first 4 positions (see Materials and methods). At position 501, bulky chemical types F, Y, W and H were also excluded. To see this figure in color, go online.