Fig. 4.

Proteome-wide off-target binding analysis of three polyclonal antibodies. Results from three polyclonal antibodies analyzed on ultra-dense peptide arrays with 12-mer peptides with a six-amino-acid lateral shift in total covering the entire human proteome. Gene origin, amino acid sequence, and relative binding intensity are shown for the peptides with the highest antibody binding for each array. A, peptides bound with high intensity by an anti-PCMT1 antibody revealed three epitopes, GAAAP (red), GRLI (yellow), and VGSGS (purple). B, an anti-TYK2 antibody shows binding to peptides containing the VTGT (red) or APRF (yellow) epitope sequences, but also to two peptides not sharing sequence similarity with the target protein (black). C, for an anti-RRP1B antibody, four epitope patterns were identified: PF-K (red), TGPS-F (yellow), TFGL (purple), and L-K (cyan). Many off-target peptides showed high antibody binding, and only one peptide originating form the RRP1B sequence was present among the top 17 peptides.