posted on 2021-02-11, 16:40authored byTien T. Dang, Lai Y. Chan, Benjamin J. Tombling, Peta J. Harvey, Edward K. Gilding, David J. Craik
Cyclotides are plant-derived peptides
that have attracted interest
as biocides and scaffolds for the development of stable peptide therapeutics.
Cyclotides are characterized by their cyclic backbone and cystine
knot framework, which engenders them with remarkably high stability.
This study reports the cystine knot-related peptidome of Rinorea
bengalensis, a small rainforest tree in the Violaceae family
that is distributed from Australia westward to India. Surprisingly,
many more acyclic knotted peptides (acyclotides) were discovered than
cyclic counterparts (cyclotides), with 32 acyclotides and 1 cyclotide
sequenced using combined transcriptome and proteomic analyses. Nine
acyclotides were isolated and screened against a panel of mammalian
cell lines, showing they had the cytotoxic properties normally associated
with cyclotide-like peptides. NMR analysis of the acyclotide ribes
21 and 22 and the cyclotide ribe 33 confirmed that these peptides
contained the cystine knot structural motif. The bracelet-subfamily
cyclotide ribe 33 was amenable to chemical synthesis in reasonable
yield, an achievement that has long eluded previous attempts to synthetically
produce bracelet cyclotides. Accordingly, ribe 33 represents an exciting
new bracelet cyclotide scaffold that can be subject to chemical modification
for future molecular engineering applications.