Synthesis, Structural Characterization, and Bioactivity of the Stable Peptide RCB-1 from Ricinus communis

Abstract

The Ricinus communis biomarker peptides RCB-1 to -3 comprise homologous sequences of 19 (RCB-1) or 18 (RCB-2 and -3) amino acid residues. They all include four cysteine moieties, which form two disulfide bonds. However, neither the 3D structure nor the biological activity of any of these peptides is known. The synthesis of RCB-1, using microwave-assisted, Fmoc-based solid-phase peptide synthesis, and a method for its oxidative folding are reported. The tertiary structure of RCB-1, subsequently established using solution-state NMR, reveals a twisted loop fold with antiparallel β-sheets reinforced by the two disulfide bonds. Moreover, RCB-1 was tested for antibacterial, antifungal, and cytotoxic activity, as well as in a serum stability assay, in which it proved to be remarkably stable.

Biologically Active Orbitides from the Euphorbiaceae Family

“…Ricinus communis L. is a plant from the Euphorbiaceae family known for the presence of the protein ricin, an extremely toxic natural poison found in high amounts in the plant. Ricin can be toxic by ingestion, inhalation, or injection [82,83]. Recently, three new peptides, designated R. communis L. biomarkers (RCB) 1-3, were identified in the plant seeds.…”

“…Recently, three new peptides, designated R. communis L. biomarkers (RCB) 1-3, were identified in the plant seeds. Those peptides comprise homologous sequences of 19 (RCB-1) or 18 (RCB-2 and RCB-3) amino acid residues, including four cysteine moieties and disulfide bonds [82]. Thus, RCB-1 consists of 19 amino acids and has two disulfide bonds, and the structure was determined to be (-Ala-Arg-Cys-Cys-Leu-Val-Met-Pro-Val-Pro-Pro-Phe-Ala-Cys-Val-Lys-Phe-Cys-Ser-) [83].…”

“…It was synthesized by SPPS with the assistance of microwave heating during the deprotection and coupling reaction steps, and then subjected to oxidative folding. Additionally, the three-dimensional structure of RCB-1 was determined [82]. RCB-2 contains 18 amino acids and two disulfide bonds, and the sequence was determined to be (-Ala-Arg-Cys-Cys-Leu-Val-Met-Pro-Val-Pro-Pro-Phe-Ala-Cys-Val-Lys-Phe-Cys-).…”

“…The peptide RCB-3 also has two disulfide bonds and has the sequence (-Ala-Arg-Cys-Cys-Leu-Val-Leu-Pro-Val-Pro-Pro-Phe-Ala-Cys-Val-Lys-Phe-Cys-) [83]. Due to their similarity to the Ib-AMP peptide family, it was suggested that the function of these RCB peptides might be related to plant defence, playing a role in seed protection, although further investigations are still suggested [82,83]. The genus Euphorbia also contains peptides.…”

“…Different concentrations of RCB-1, ranging from 160 to 0.625 µM, were used. The compound RCB-1 was found to be active against only P. aeruginosa, although it was tested against a set of human pathogens (E. coli, S. aureus, and C. albicans) and plant pathogens (Erwinia carotovora, Erwinia amylovora, and Aspergillus fumigatus) [82].…”