Distribution of cicular peptides in plants: Large scale mapping of cyclotides in the Violaceae
(English)Manuscript (preprint) (Other academic)
During last decade there has been increased interest in the small, cysteine-rich cyclotide proteins found in plant species of the violet family (Violaceae). These cyclotides consist of a circular chain of approximately 30 amino acids, including six cysteines that form three disulfide bonds, arranged in a cyclic cystine knot motif. In this study we map the occurrence and distribution of cyclotides in the Violaceae. Plant material was obtained from herbarium sheets containing samples up to 200 years old. Even the oldest specimens exhibited a remarkable stability of cyclotides in the preserved leaves, with no degradation products observable, making them one of the most stable proteins in nature. We analyzed the cyclotide content in over 200 samples covering 17 of the 23 genera, and positively identified cyclotides in almost 150 of approximately 900 known species in the Violaceae. Each species contained a unique set of between one and 25 cyclotides, of which many were exclusive to individual species. The estimated number of different cyclotides in the Violaceae is 5,000-25,000. We conclude that the Violaceae is an extremely rich source of cyclotides, and we propose that cyclotides are ubiquitous among all Violaceae species.
IdentifiersURN: urn:nbn:se:uu:diva-131137OAI: oai:DiVA.org:uu-131137DiVA: diva2:353444