Figure 2
Screening and selection of peptide binders to SARS-CoV-2 S protein. (a) Peptides P2-P11 represent wild-type versions of the original 27-mer ACE2 N-terminal alpha helix. They were designed as 18-mers spanning the length of the original fragment with 17 amino acids overlapped. The ACE2 fragment is predicted to bind to the SARS-CoV2 S protein via residues shown in bold12. (b) Normalized binding signal of the ACE2-derived peptide variants show little to no binding to SARS-CoV2 S1 protein. There is an apparent trend for increased binding from the peptide fragments overlapping the center of the WT sequence and P7 shows the highest binding signal with a z-score of 1.3 when exposed to 50 µg/mL of S1 protein. (c) Normalized binding signal of the 14 peptides selected from microarray screening experiments for further characterization. 10 peptides were selected from the pool of ACE2 mutants, 3 were selected from the pool of modeled sequences, and one non-binding sequence was selected for comparison. All sequences selected had a Z-score > 2 on the 50 µg/mL S1 protein array, except for P481. (d) Sequences of the 14 peptides selected for synthesis with N-terminus biotin attached via a PEG4 spacer. **Note that P28 was not able to be synthesized by the vendor. (e) Binding curves of biotinylated peptides to immobilized SARS-CoV2 S1 protein in ELISA plate-based assay. Four peptides (P89, P100, P168 and P180) showed higher binding affinity than the original ACE2 fragment (SBP1) and were selected for further characterization.
