Does Cysteine Rule (CysR) Complete the CendR Principle? Increase in Affinity of Peptide Ligands for NRP-1 Through the Presence of N-Terminal Cysteine.

The structure-activity relationship of branched H-Lys(Arg)-Dab-Dhp-Arg-OH sequence analogues, modified with Cys-Asp or Cys at N-terminal amino acids (Lys, Arg), in VEGF-A/Neuropilin-1 complex inhibition is presented. The addition of Cys residue led to a 100-fold decrease in the IC value, compared to the parent peptide. The change occurred regardless of coupling Cys to the free N-terminal amino group present in the main or the side chain. A few analogues extended by the attachment of Cys at the N-terminus of several potent NRP-1 peptide ligands documented in the literature are also presented. In all studied cases, the enhancement of inhibitory properties after the addition of Cys at the N-terminus is observed. It is particularly evident for the tetrapeptide derived from the C-terminus of VEGF-A (KPRR), suggesting that extending the K/RXXK/R motif (CendR) with the Cys moiety can significantly improve affinity to NRP-1 of CendR peptides.