Fig. 1.

Optimization and improvement of the peptide. (A) Main binding regions between human programmed cell death protein 1 (hPD-1) and human programmed death-ligand 1 (hPD-L1). The key amino acid residues through which it binds programmed cell death protein 1 (PD-1) are labeled. The region including A121 K124 R125 in PD-L1 shows sequence homology with nABP284. (B) AutoDock simulation provided evidence for the hypothesis that the imidazole ring on histidine could bind to the cleft between Y68 and E136 in PD-1. (C) Sequence of nABP284 and nABPD1, nABPD1 was optimized from nABP284 by adding branched chains (SHHHRL) with three consecutive histidine residues (HHH) on the N-termini. (D) Structural formula of HHH.