2.2. Linear peptide synthesis
The sequences we used for the design of linear peptides of the RBD, S2,
and NP of SARS-CoV-2 were obtained from GenBank under accession numbers
NC_045512.2 and MN908947.3. For epitope screening of RBD and NP, we
designed panels of linear peptides spanning the entire sequence of the
RBD and NP protein of SARS-CoV-2 (each peptide contains 20 amino acid
residues with 5 residues overlapping with the adjacent peptides). For
epitope screening of S2, only three non-overlapping individual peptides,
FE-18, FI-22, and CK-16, with lengths ranging from 16-22 aa, were used.
All the peptides were synthesized by Pepmic company (China). Peptide
synthesis was performed using a standard solid-phase Fmoc method.
Peptides were purified to homogeneity (purity more than 90%) by HPLC
and identified by laser desorption mass spectrometry. Peptides were used
individually or as pooled sets. Three peptides were combined to form one
pooled peptide set. To obtain a stock solution, lyophilized individual
peptides were dissolved in deionized water or Dimethyl Sulfoxide 3%
(DMSO, Sigma Aldrich, Germany) according to the manufacturer’s
instruction. Amino acid sequences of peptide sets are shown in table 1.