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Open AccessArticle

Isolation of Cysteine-Rich Peptides from Citrullus colocynthis

Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria
Department of Plant Biotechnology, Shiraz University, Shiraz 7144165186, Iran
Department of Plant Protection, Shiraz University, Shiraz 7144165186, Iran
Department of Plant Breeding and Biotechnology, SANRU, Sari P.O. Box 578, Iran
Department of Biology, Shiraz University, Shiraz 7194684795, Iran
Author to whom correspondence should be addressed.
Biomolecules 2020, 10(9), 1326;
Received: 15 August 2020 / Revised: 8 September 2020 / Accepted: 11 September 2020 / Published: 16 September 2020
The plant Citrullus colocynthis, a member of the squash (Cucurbitaceae) family, has a long history in traditional medicine. Based on the ancient knowledge about the healing properties of herbal preparations, plant-derived small molecules, e.g., salicylic acid, or quinine, have been integral to modern drug discovery. Additionally, many plant families, such as Cucurbitaceae, are known as a rich source for cysteine-rich peptides, which are gaining importance as valuable pharmaceuticals. In this study, we characterized the C. colocynthis peptidome using chemical modification of cysteine residues, and mass shift analysis via matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. We identified the presence of at least 23 cysteine-rich peptides in this plant, and eight novel peptides, named citcol-1 to -8, with a molecular weight between ~3650 and 4160 Da, were purified using reversed-phase high performance liquid chromatography (HPLC), and their amino acid sequences were determined by de novo assignment of b- and y-ion series of proteolytic peptide fragments. In silico analysis of citcol peptides revealed a high sequence similarity to trypsin inhibitor peptides from Cucumis sativus, Momordica cochinchinensis, Momordica macrophylla and Momordica sphaeroidea. Using genome/transcriptome mining it was possible to identify precursor sequences of this peptide family in related Cucurbitaceae species that cluster into trypsin inhibitor and antimicrobial peptides. Based on our analysis, the presence or absence of a crucial Arg/Lys residue at the putative P1 position may be used to classify these common cysteine-rich peptides by functional properties. Despite sequence homology and the common classification into the inhibitor cysteine knot family, these peptides appear to have diverse and additional bioactivities yet to be revealed. View Full-Text
Keywords: Cucurbitaceae; Citrullus colocynthis; peptides; trypsin inhibitor; knottin Cucurbitaceae; Citrullus colocynthis; peptides; trypsin inhibitor; knottin
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Shahin-Kaleybar, B.; Niazi, A.; Afsharifar, A.; Nematzadeh, G.; Yousefi, R.; Retzl, B.; Hellinger, R.; Muratspahić, E.; Gruber, C.W. Isolation of Cysteine-Rich Peptides from Citrullus colocynthis. Biomolecules 2020, 10, 1326.

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