What are Cyclotides

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What are Cyclotides?
Uses of Cyclotides
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Discovery of Cyclotides
Sequences
Biological Activity
Structures
Topological Features
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Cyclotide Genes
Cystine Knots
Other Circular Proteins
Cybase: The Cyclotide Database
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Cyclotides are small disulfide-rich proteins that have the unusual feature of a cyclic backbone (hence the name cyclo - peptides). They contain six conserved cystine residues that are arranged in a cystine knot topology in which two disulfide bonds and their connecting backbone segments form an embedded ring in the structure that is penetrated by a third disulfide bond, as shown below.

Cyclotides have a range of interesting biological activities including anti-HIV and neurotensin inhibition, anti-microbial activity and insecticidal activity. They are found in a variety of tropical plants from the Rubiaceae and Violaceae families.

The structure of kalata B1 showing the distorted beta-sheet topology and the loop nomenclature enabled by the cyclic backbone.