This family contains a set of cyclic peptides with a variety of activities. The structure consists of a distorted triple-stranded beta-sheet and a cysteine-knot arrangement of the disulfide bonds [2]. Cyclotides can be separated into two subfamilies, namely bracelet and moebius. The bracelet cyclotide subfamily tends to contain a larger number of positively charged residues and has a bracelet-like circularisation of the backbone [2]. The moebius cyclotide subfamily contains a backbone twist due to a cis-Pro peptide bond and may conceptually be regarded as a molecular Moebius strip [2].

1: Solution structure by NMR of circulin A: a macrocyclic knotted peptide having anti-HIV activity. Daly NL, Koltay A, Gustafson KR, Boyd MR, Casas-Finet JR, Craik DJ; J Mol Biol 1999;285:333-345. PMID:9878410

2: Plant cyclotides: A unique family of cyclic and knotted proteins that defines the cyclic cystine knot structural motif. Craik DJ, Daly NL, Bond T, Waine C; J Mol Biol 1999;294:1327-1336. PMID:10600388