Cyclotides, a Novel Ultrastable Polypeptide Scaffold for Drug Discovery

Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, CA 90033, USA.
Current pharmaceutical design (Impact Factor: 3.45). 12/2011; 17(38):4294-307. DOI: 10.2174/138161211798999438
Source: PubMed


Cyclotides are a unique and growing family of backbone cyclized peptides that also contain a cystine knot motif built from six conserved cysteine residues. This unique circular backbone topology and knotted arrangement of three disulfide bonds makes them exceptionally stable to thermal, chemical, and enzymatic degradation compared to other peptides of similar size. Aside from the conserved residues forming the cystine knot, cyclotides have been shown to have high variability in their sequences. Consisting of over 160 known members, cyclotides have many biological activities, ranging from anti-HIV, antimicrobial, hemolytic, and uterotonic capabilities; additionally, some cyclotides have been shown to have cell penetrating properties. Originally discovered and isolated from plants, cyclotides can also be produced synthetically and recombinantly. The high sequence variability, stability, and cell penetrating properties of cyclotides make them potential scaffolds to be used to graft known active peptides or engineer peptide-based drug design. The present review reports recent findings in the biological diversity and therapeutic potential of natural and engineered cyclotides.

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    • "ini - scaffolds that are known to have good bioavailability but are still amendable to chemical synthesis . For example , cyclotides are small head - to - tail cyclised disulfide rich peptides , which have the potential to reach intracellular targets ( Greenwood et al . , 2007 ) . These scaffolds can be used as hosts for grafted active sequences ( Gould et al . , 2011 ) . Recently , recombinant expression of cyclotides in yeast by a split - intein approach coupled to a phenotypic screen has been developed thereby opening the doors to screen genetically encoded cyclotide - based libraries in eukaryotic cells ( Jagadish et al . , 2015 ) ."
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    ABSTRACT: Cyclotides are disulfide-rich cyclic peptides produced by plants with the presumed natural function of defense agents against insect pests. They are present in a wide range of plant tissues, being ribosomally synthesized via precursor proteins that are posttranslationally processed to produce mature peptides with a characteristic cyclic backbone and cystine knot motif associated with their six conserved cysteine residues. Their processing is not fully understood but involves asparaginyl endoproteinase activity. In addition to interest in their defense roles and their unique topologies, cyclotides have attracted attention as potential templates in peptide-based drug design applications. This chapter provides protocols for the isolation of cyclotides from plants, their detection and sequencing by mass spectrometry, and their structural analysis by NMR, as well as describing methods for the isolation of nucleic acid sequences that encode their precursor proteins. Assays to assess their membrane-binding interactions are also described. These protocols provide a "starter kit" for researchers entering the cyclotide field.
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