Table of Contents  
Year : 2012  |  Volume : 3  |  Issue : 3  |  Page : 169-177  

The bountiful biological activities of cyclotides

Department of Pharmacology, Tulane University, School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112, USA

Date of Web Publication10-Aug-2012

Correspondence Address:
Samantha L Gerlach
Department of Pharmacology, Tulane University, School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2229-5186.99559

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Cyclotides are exceptionally stable circular peptides (28-37 amino acid residues) with a unique cyclic cystine knot (CCK) motif that were originally discovered through ethnobotanical investigations and bioassay-directed natural products screenings. They have been isolated from four angiosperm families (Violaceae, Rubiaceae, Curcurbitaceae, and Fabaceae), and they exhibit a wide range of bioactivities including antibacterial/antimicrobial, nematocidal, molluscicidal, antifouling, insecticidal, antineurotensin, trypsin inhibiting, hemolytic, cytotoxic, antitumor, and anti-HIV properties. Reports indicate that the mechanism of cyclotide bioactivity is the ability to target and interact with lipid membranes via the development of pores. Additionally, the nature of their surface-exposed hydrophobic patch and CCK play integral roles in the potency of cyclotides. Their extraordinary stability and flexibility have recently allowed for the successful grafting of analogs with therapeutic properties onto their CCK framework. This achievement, coupled with the myriad of useful naturally occurring bioactivities displayed by cyclotides, makes them appealing candidates in drug design and crop management.

Keywords: Bioactivity, cancer, cyclotides, HIV, host defense

How to cite this article:
Gerlach SL, Mondal D. The bountiful biological activities of cyclotides. Chron Young Sci 2012;3:169-77

How to cite this URL:
Gerlach SL, Mondal D. The bountiful biological activities of cyclotides. Chron Young Sci [serial online] 2012 [cited 2020 Feb 18];3:169-77. Available from:

   Discovering Cyclotides Top

The discovery of cyclotides is attributed to ethnobotanical investigations and bioassay-directed screenings of potentially therapeutic plants. In 1965, a professor of Pharmacognosy at Uppsala University, Dr. Finn Sandberg, reported his observations of indigenous plant use in the Central African Republic. A remedy from the plant "Wetegere" (Gbaya language), later identified as Oldenlandia affinis (Roem. & Schult.) DC (Rubiaceae), was administered to hasten uterine contractions. [1] In the 1970s, the Norwegian physician Lorents Gran participated in a Red Cross Relief Mission which included harvesting medicinal plants in the northern Congo of Africa. Dr. Gran observed women of the Lulua tribe (Tsjiluba language) harvesting the above-ground tissues of a plant called "kalata-kalata" which subsequently was taxonomically verified as O. affinis. Elder healers prepared an aqueous decoction (~1 part powdered aerial tissue to 1 part boiling water) and then ingested the "tea" to induce labor. Use of the plant as an uterotonic was surrounded by a degree of secrecy among the women, and although the decoction produced rapid deliveries, in some cases severe spasms ensued and emergency caesarian sections were required. [2],[3],[4],[5]

Upon returning to his native country, Dr. Gran isolated several polypeptides in samples of O. affinis extracts that exhibited remarkably strong uterotonic activity. With the aid of protein chemist, Dr. Knut Sletten, the principal bioactive peptide, now named kalata B1, was identified and almost fully sequenced. [6] This peptide was speculated to be a cyclic structure; however, it was exceptionally resistant to degradation and N-terminal amino acid sequencing, and at the time the available enzymatic tests were insufficient to provide conclusive proof of the cyclic nature of kalata B1. Therefore, the complete sequence of the prototypic cyclotide, kalata B1, was not reported until the three-dimensional solution structure was confirmed using two-dimensional magnetic resonance (NMR) spectroscopy and distance-restrained simulated annealing. [7]

At around this time (mid-1990), three independent research facilities reported the discovery of macrocyclic peptides with six cystine residues isolated from violaceous and rubiaceous plants. During a screening for new saponins, the hemolytic violapeptide I (from Viola sp.; Violaceae) was isolated, and the finding was published in a German specialist trade journal. [8] In 1994, the National Cancer Institute in the USA was evaluating a collection of plants for anti-HIV activity; the cyclotides, circulin A and circulin B, were characterized from extracts of the tropical tree Chassalia parvifolia K. Schum (Rubiaceae). [9] Finally, Merck Laboratory Researchers (USA) identified cyclopsychotride A from extracts of Psychotria vellosiana Benth. (Rubiaceae) while testing natural products for neurotensin antagonistic activity. [10] During the next decade, additional reports on the isolation of polypeptides with a circular nature and unique cyclic cystine knot (CCK) motif from violaceous, rubiaceous, and cucurbitaceous plants were reported which prompted the formal designation of the cyclotides as a plant protein family in 1999. [11],[12],[13]

   Cyclotide-Producing Plant Families Top


Roughly 198 cyclotides have been discovered from 36 species in the Violaceae, Rubiaceae, Cucurbitaceae, and Fabaceae plant families [Table 1]. Seventy-two percent of sequenced cyclotides have been characterized from 24 species of Violaceae, and cyclotides are present in every violaceous species analyzed. The family comprises ~23 genera and 800 species of cosmopolitan shrubs, herbs, and rarely trees [16] and takes its name from the genus Viola, the violets/pansies, which are tiny herbaceous perennials. In terms of economic revenue, violaceous flowers are frequently used in the fragrance and cuisine industries. Traditional Chinese medicine routinely incorporates the violets into healing practices, as several species have antioxidant anthocyanins, vitamin A and C, glycosides, saponins, flavonoids, carotenoids, and cyclotides. Furthermore, extracts from Viola odorata L., a species rich in cyclotides, display antineoplastic, antiviral, anti-HIV, and antitumor effects. [17]
Table 1: Known taxonomic distribution and abundance of cyclotides in angiosperms

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The distribution of cyclotides in Rubiaceae is more limited (i.e., many species screened for cyclotides do not express them) compared with Violaceae, yet the extent to which cyclotides are present in Rubiaceae remains unclear, in part because fewer than 10% of the existing rubiaceous species have been evaluated for cyclotide expression. Rubiaceae is the fourth largest angiosperm family with ~650 genera and 13,000 species of shrubs and small trees that occur mostly in tropical and subtropical regions of the world. [18] Alkaloids are prevalent throughout the family, and familial members are an important source of coffee, timber, dyes, ornamentals, and prescription medicines. [19],[20],[21]


Only two cucurbitaceous cyclotides have been isolated from Momordica cochinchinensis (Lour.) Spreng. These cyclotides, MCoT-I and MCoT-II, inhibit trypsin, an enzyme essential for nutrition in mammalian systems, and are circular with the CCK motif yet they share no further sequence similarity to other cyclotides; therefore, these peptides have been described as cyclic knottins, trypsin inhibitors, or cyclotides. [22],[23] The family of the melons and squashes, Cucurbitaceae, comprises ~125 genera and 960 species of predominantly annual vines. [24] The genus Momordica consists of ~60 species of climbing herbs and lianas that have a history of use in Chinese folk medicine. [25] A systematic search for cyclotides in Cucurbitaceae is warranted to explain their distribution.


The most recent addition to the cyclotide-expressing plant families is Fabaceae, the family of the legumes; [26] 24 novel cyclotides have been isolated from Clitoria ternatea L. Fabaceae is the third largest family of angiosperms with ~730 genera and over 19,400 species of mainly herbs and large trees. Throughout history, humans have heavily relied upon fabaceous plants for agricultural and medicinal purposes. Fabaceous species provide one-third the global crop production. The cyclotide-expressing genus Clitoria consists of ~60 species of woody plants with papilionaceous flowers and leguminous fruits. Remedies of C. ternatea have been used to enhance fertility, control menstruation, treat gonorrhea, induce vomiting, and provide an antidote to animal bites in traditional healing systems throughout Asia, Africa, and South America. [27]

   Cyclotide Structure Top

Cyclotides are circular proteins characterized by 27-38 amino acids and a unique cystine knot topology of six highly conserved cystine residues linked via three disulfide bonds as illustrated in [Figure 1]. The disulfide bonds (in yellow) connect cystine residues (Roman numerals I-VI) to create a ring and knotted configuration that generates six backbone segments (loops 1-6) between the successive residues. All cyclotides have an associated secondary structure involving a b-hairpin centered in loop 5. [13],[28]
Figure 1: A representation of cyclotide structure and sequence. Kalata B1 (PDB ID 1nb1) has a seamless peptide backbone with three disulfides (yellow) connecting cysteine residues (Roman numerals). Backbone segments are labeled loops 1– 6. Amino acid sequences are provided.

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Cyclotides can be divided into three subfamilies. Möbius cyclotides have a cis-peptide bond prior to the Proline (Pro, P) in loop 5 which creates a twist in the conceptual ribbon of the peptide backbone; bracelet cyclotides lack this bond. Members of the Möbius subfamily generally show less variation in loop size and amino acid sequence, have fewer positively charged residues, and are less hydrophobic compared with bracelet cyclotides. The third subfamily, trypsin inhibitors, has been suggested, but as mentioned only two trypsin inhibitor cyclotide sequences have been discovered. Although structural variations provide the basis for subfamily delineation, a few natural chimeras (i.e., cyclotides containing some loops with characteristics of the Möbius subfamily and others with characteristics of the bracelet subfamily) have been described. [29] As additional cyclotides are discovered, subfamily classifications may require evaluation.

The primary structural elements of cyclotides include a cystine knot associated with a distorted triple-stranded b-sheet stabilized by a number of hydrogen bonds, an almost strictly conserved glutamic acid (Glu, E) in loop 1 that is involved in hydrogen bonding interactions with loop 3, and a surface-exposed hydrophobic patch that influences retention time on RP-HPLC and bioactivity. [30],[31] The highly conserved asparagine (Asn, N) or occasionally aspartic acid (Asp, D) in loop 6 is thought to be necessary for cyclization. [32] Almost all cyclotides have a glycine (Gly, G) residue preceding Cys IV [33] which readily adopts a positive f angle required for the type II b-turn needed to connect loop 3 to the cystine knot. [30]

   Biologically Active Properties of Cyclotides Top

In general, the use of peptides as pharmaceuticals has been limited due to inadequate stability and bioavailability under physiological conditions. However, the exceptional stability, sequence plasticity, and framework flexibility of cyclotides, coupled with their numerous potent bioactivities resulting from their ability to target lipid membranes, emphasize the assertion that these cyclic polypeptides are ideal candidates for studies in the development of novel drugs and biopesticides. [34],[35] The speculated natural function of cyclotides is in plant defense as illustrated by several reports of their antibacterial/antimicrobial, [36] insecticidal, [37],[38] antihelmintic, [39],[40],[41] nematocidal, [42] antifouling, [43] and molluscicidal properties. [44] The use of cyclotides in human health applications was first explored during the discovery of kalata B1, and although its uterotonic activity was established in rat, rabbit, and human uteri, it is not recommended as an oxytocic agent because of the severe side effects. [4] During the past decade, a profusion of bioactivity-directed research demonstrates that cyclotides display an assortment of activities, including antineurotensin, [10] trypsin inhibiting, [22],[23] hemolytic, [30],[31] cytotoxic/antitumor, [45],[46],[47],[48],[49],[50],[51],[52],[53],[54],[55],[56] and anti-HIV activities; [9],[29] several of these properties have prospective therapeutic relevance.

Table construction to assemble cyclotide bioactivities

In an effort to amass the literature available pertaining to cyclotide biological activity and concisely illustrate it using informative reference tables, a series of SciFinder Scholar searches was first performed, and [Table 2] shows the number of articles retrieved when using the search key word function and then searching either cyclotide by itself or cyclotide plus a biological activity. After reviewing each abstract and eliminating irrelevant publications, the decision was made to summarize those bioactivities that may have the greatest potential in agricultural and pharmaceutical applications (i.e., host defense, anticancer, and anti-HIV properties); any manuscripts that had not been read were obtained for review. [Table 3],[Table 4],[Table 5] and [Table 6] provide a wealth of information summarizing the bioassays and potency of evaluated cyclotides in/against the specified bioactivity. The remainder of this review highlights the factors affecting cyclotide potency and describes their potential use as natural defense agents and in the treatment of cancer and HIV.
Table 2: Results of SciFinder Scholar searches for cyclotide bioactivity literature

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Table 3: Cyclotides exhibiting antibacterial, antimicrobial, insecticidal, or molluscicidal activity

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Table 4: Cyclotides displaying antihelminthic activity

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Table 5: Cyclotides exhibiting cytotoxic or antitumor activity

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Table 6: Cyclotides exhibiting anti.HIV activity

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   Structural and Molecular Features of Cyclotides Impact Bioactivity Top

The mechanism of cyclotide bioactivity is membrane interaction

Changes in cyclotide bioactivity have been reported when different targets or cyclotides are compared which may indicate that a variety of membrane and cyclotide characteristics influence bioactivity. An increasing body of evidence suggests that membrane interactions and the formation of pores are responsible for cyclotide bioactivity. [47],[50],[52],[69],[70],[71],[72],[73] For instance, reports indicate that kalata peptides selectively bind to bacterial membranes, [69],[74] and some cyclotides may form discrete pores on the external surface of nematodes and thereby interact with the lipid-rich epicuticle layer at the surface of the worm. [42]

Furthermore, the antitumor properties of cyclotide, cycloviolacin O 2 (CyO 2 ) are caused first by the disruption of lipid membranes followed by leakage of contents from whole cells as well as liposomes. [70] CyO 2 causes rapid (within 5 minutes) disruption of lipid bilayers and is selectively cytotoxic in a dose-dependent manner. As a result of their pore-forming properties, CyO 2 and psyle cyclotides chemosensitize drug-resistant breast cancer cells to doxorubicin. [50],[70] As illustrated in [Table 5], cyclotides display potent cytotoxic properties against a range of cancer cell types, and a recent study evaluating neutral (zwitterionic) membranes with and without cholesterol and/or anionic lipids demonstrates that the membrane binding and disrupting properties of cyclotides are dependent on lipid composition since CyO 2 , a member of the bracelet subfamily, was a potent membrane disrupter with selectivity toward anionic membranes, while Möbius cyclotides, kalata B1 and kalata B2, display significantly less lytic activity toward those membranes. [72],[75]

The potency of anti-HIV activity for cyclotides (as exemplified in [Table 6]) is also influenced via membrane interactions. For example, kalata B1 is sequestered on the membrane most likely through self-association and then forms conductive pores with channel-like activity via the insertion of oligomers into the lipid bilayers of membranes. [76] Furthermore, specific interactions with phospholipids containing phosphatidylethanolamine (PE) headgroups and nonspecific lipid hydrophobic interactions can alter anti-HIV potency. Kalata B1 can target and disrupt HIV particles that have raft-like membranes and are rich in PE phospholipids. [71] The activity is not dependent on the recognition of chiral receptors since the all D-enantiomer of kalata B1 that was synthesized was still active in cytotoxic and hemolytic assays. [73] Taken together, this body of evidence indicates that the mechanism of cyclotide bioactivity is membrane interactions via pore formation.

A defined hydrophobic patch influences bioactive potency

One prominent characteristic of cyclotides is a hydrophobic patch which is formed by solvent-exposed amino acids that protrude outward to the molecular surface due to the occupation of the core by the disulfide bonds of the cystine knot; this feature impacts antibacterial, [36],[57] insecticidal, [38] cytotoxic, [75] anti-HIV, [64],[65] and hemolytic activities [77],[78] such that increases in the hydrophobic surface area correlate with enhanced bioactivities. [64] As mentioned, the cyclotide subfamilies, bracelet and Möbius, differ in the absence and presence of a cis-Pro peptide bond in loop 5, respectively. These subfamilies also differ in their orientation in the membrane due to variations in the distribution of surface-exposed hydrophobic amino acid residues and their net charge. For instance, the bracelet cyclotide, CyO 2 , interacts with the lipid bilayers via the hydrophobic segments of loops 2 and 3, while the hydrophobic loops 5 and 6 are buried in the membrane of the Möbius peptide varv A. This feature impacts bioactivity in that bracelet cyclotides tend to be more potent. Interestingly, chimeric cyclotides such as kalata B8 and psyle A demonstrate the importance of the amphiphatic structure of cyclotides in that they resemble Möbius cyclotides except for their loop 5 composition. In this loop, the loss of hydrophobic residues generally seen in Möbius cyclotides disrupts their amphipathicity and decreases cytotoxicity by greater than 30-fold. [72],[75]

Two amino acid residues that can impact potency of several bioactivities are the conserved Glu in loop 1 and tryptophan (Trp, W). For instance, the esterification of Glu in the bracelet cyclotide, CyO 2 , results in a 48-fold decrease in cytotoxic potency [48] and a near loss of antibacterial activity against  Salmonella More Details sp. [57] Apparently Glu does not similarly affect the Möbius cyclotide, varv A, which displays only a three-fold decrease in potency when the residue is esterified. The hydrophobic Trp residue common in many cyclotides plays an important role in bioactivity because when peptides containing Trp bind to the membrane, Trp is buried into the lipid bilayers and enhances cytotoxicity. Hydroxlyation of Trp in models of varv A and CyO 2 results in dramatic decreases in cytotoxicity. [72],[75]

An intact circular backbone is essential for several cyclotide bioactivities

The unique features of cyclotides (i.e., circular structure and CCK motif) are considered crucial traits impacting their bioactivity. Indeed, the reduction/alkylation of disulfide bonds and/or linearization of the circular backbone can result in a complete loss of antibacterial, cytotoxic, or hemolytic activity. [30],[48],[58],[79] Reduced peptides in general are significantly more susceptible to denaturation via enzymes or chemicals compared with oxidized species. [80],[81] However, psyle C is a linear peptide (or "uncyclotide" as suggested by Nguyen and colleagues) [58] that retains the other unique features of cyclotides, and it is active against lymphoma, breast cancer, drug-resistant breast cancer, and chemosensitizes cells to the anticancer drug doxorubicin. [50],[51],[52] Violacin A is also an uncyclotide although it has dramatically reduced hemolytic activity compared with other cyclotides which is thought to be attributed to its atypically low hydrophobicity and linear nature. [78] Hedyotide B2, a third naturally occurring uncyclotide, has no bacterial activity. [58] Thus, it appears that forced reduction results in a loss of activity, and further studies on the retained cytotoxicity of psyle C and bioactivity potency of the other uncyclotides may shed new insight on the importance of the CCK.

Cyclotides may be therapeutic and useful scaffolds in drug design

Recently, analogs with vascular endothelial growth factor (VEGF) antagonism were successfully grafted onto the CCK framework of kalata B1. The normal function of VEGF is the creation of new blood vessels; however, when VEGF is overexpressed, it can contribute to disease. Solid cancers will not grow beyond a limited size without a supply of blood. Cancers that express VEGF have an ample source of blood and are able to grow and metastasize. Therefore, the development of stable peptide analogs with VEGF antagonism which are grafted onto cyclotides is a novel approach that may be useful in the treatment of diseases where angiogenesis is an important component. [35]

Additionally, cyclotides display potent, salt-dependent antibacterial properties against both Gram-negative and Gram-positive bacteria as illustrated in [Table 3]. [36] Since the cyclic structure and cystine knot motif of cyclotides closely resembles current antimicrobial drug leads, such as microcin J25, cyclotides may be useful templates for designing novel antibiotics. [Table 3] and [Table 4] also emphasize the fact that cyclotides can inhibit the movement, growth, and development of insect larva and parasites and increase mortality. [37],[38],[59],[60],[61] Taken together, these reports support the supposition that cyclotides alone or as scaffolds can deter or be engineered to inhibit interactions associated with cancer, infectious disease, and pest management.

   Acknowledgments Top

The following review was supported by a Louisiana Board of Regents Grant.

This review manuscript has been read and approved by Samantha L. Gerlach, and to the best of the author's knowledge the manuscript represents honest work of which the author is responsible for the content and writing of the manuscript.

   References Top

1.Sandberg F. Étude sur les plantes médicinales et toxiques d'Afrique équatoriale. Cahièrs de la Maboké. 1965. 12 Rue de Buffon, Paris, Tome III, Fascicule. 1.  Back to cited text no. 1
2.Gran L. Oxytocic principles of Oldenlandia affinis. Lloydia 1973a;36:174-8.  Back to cited text no. 2
3.Gran L. Isolation and oxytocic peptide from Oldenlandia affinis by solvent extraction of tetraphenylborate complexes and chromatography on sephadex LH-20. Llyodia 1973b;36:207-8.  Back to cited text no. 3
4.Gran L. On the effect of a polypeptide isolated from "Kalata-Kalata" (Oldenlandia affinis) on the oestrogen dominated uterus. Acta Pharmacol Toxicol (Copenh) 1973c;33:400-8.  Back to cited text no. 4
5.Gran L, Sandberg K, Sletten K. A plant containing uteroactive peptides used in African traditional medicine. J Ethnopharmacol 2000;70:197-203.  Back to cited text no. 5
6.Sletten K, Gran L. Some molecular properties of kalatapeptide B-1. A uterotonic polypeptide from Oldenlandia affinis DC. Meddelelser fra Norsk farmaceutisk selskap. 1973;7-8:69-82.  Back to cited text no. 6
7.Saether O, Craik DJ, Campbell ID, Slettn K, Juul J, Norman DG. Elucidation of the primary and three-dimensional structure of the uterotonic polypeptide kalata B1. Biochemistry. 1995;34:4147-58.  Back to cited text no. 7
8.Schøpke T, Hasan AMI, Kraft R, Otto A, Hiller K. Hämolyttisch aktive Komponenten aus Viola tricolor L. und Viola arvensis Murray. Sci Pharm 1993;61:145-53.  Back to cited text no. 8
9.Gustafson KR, Sowder II RC, Henderson LE, Parsons IC, Kashman Y, Cadellina II JH et al. Circulins A and B: novel HIV-inhibitory macrocyclic peptides from the tropical tree Chassalia parvifolia. Biochem Biophys Res Commun 1994;116:9337-8.  Back to cited text no. 9
10.Witherup KM, Bogusky MJ, Anderson PS, Ramjit H, Ransom RW, Wood T, et al. Cyclophsychotride A, a biologically active 31-residue cyclic peptide isolated from Psychotria longipes. J Nat Prod 1994;57:1619-25.  Back to cited text no. 10
11.Claeson P, Göransson U, Johansson S, Luijendijk T, Bohlin L. Fractionation protocol for the isolation of polypeptides from plant biomass. J Nat Prod 1994;61:77-81.  Back to cited text no. 11
12.Göransson U, Luijendijk T, Johansson S, Bohlin L, Claeson P. Seven novel macrocyclic polypeptides from Viola arvensis. J Nat Prod 1999;62:283-6.  Back to cited text no. 12
13.Craik DJ, Daly NL, Bond T, Waine C. Plant cyclotides: a unique family of cyclic knotted proteins that defines the cyclic cysteine knot structural motif. J Mol Bio 1999;294:1327-36.  Back to cited text no. 13
14.Cybase: The Database of Cyclic Proteins. The University of Queensland Australia, The Institute for Biomolecular Science.; [updated 2012 Jan 18; cited 2012 Jan 17] Available from:  Back to cited text no. 14
15.Wang CK, Kaas Q, Chiche L, Craik DJ. CyBase: a database of cyclic protein sequences and structures, with applications in protein discovery and engineering. Nucleic Acids Res 2008; 36:D206-10.  Back to cited text no. 15
16.Angiosperm phylogeny website, Missouri Botnaical Garden.; c2000-present [updated 2011 May 11; cited 2012 Jan 17] Available from:  Back to cited text no. 16
17.Yance D, Valentine A. Herbal Medicine, Healing and Cancer. Chicago (IL): Keats Publishing; 1999.  Back to cited text no. 17
18.Delprete PG. Rubiaceae. In: Smith NP, Heald SV, Henderson A, Mori SA, Stevenson DW, editors. Flowering Plant Families of the American Tropics. New York: New Your Botanical Garden Press; 2004. p. 328-33.  Back to cited text no. 18
19.Cronquist A. An Integrated System of Classification of Flowering Plants.New York (NY): Columbia University Press; 1981.  Back to cited text no. 19
20.Zomlefer WB. Guide to Flowering Plant Families. Chapel Hill (NC): The University of North Carolina Press; 1994.  Back to cited text no. 20
21.Farnsworth NR. The role of ethnopharmacology in drug development. Ciba Foundation Symp 1990;154:2-21.  Back to cited text no. 21
22.Hernandez J, Gagnon J, Chiche L, Nguyen T, Andrieu J, Heitz A, et al. Squash trypsin inhibitors from Momordica cochinchinensis exhibit an atypical macrocyclic structure. Biochemistry 2000;39:5722-30.  Back to cited text no. 22
23.Felizmenio-Quimio ME, Daly NL, Craik DJ. Circular proteins in plants: solution structure of a novel macrocyclic trypsin inhibitor from Mormordica cochinchinensis. J Biol Chem 2001;276:22875-82.  Back to cited text no. 23
24.Jeffrey C. A new system of Cucurbitaceae. Bot Zhurn 2005;90:332-5.  Back to cited text no. 24
25.Jiratchariyakul W, Wiwat C, Vongsakul M, Somanabandu A, Leelamanit W, Fujii I, et al. HIV inhibitor from Thai bitter gourd. Planta Med 2001;67:350-3.  Back to cited text no. 25
26.Poth AG, Colgrave ML, Philip R, Kerenga B, Daly NL, Anderson MA, et al. Discovery of cyclotides in the Fabaceae plant family provides new insights into the cyclization, evolution, and distribution of circular proteins. ACS Chem Biol 2011;6:345-5.  Back to cited text no. 26
27.Fantz PR. Ethnobotany of Clitoria (Leguminosae). Econ Bot 1991;45:511-20.  Back to cited text no. 27
28.Craik DJ, Daly NL, Mulvenna J, Plan MR, Trabi M. Discovery, structure and activities of the cyclotides. Curr Protein Pept Sci 2004;5:297-315.  Back to cited text no. 28
29.Bokesch HR, Pannell LK, Cochran PK, Sowder RC, McKee TC, Boyd MR. A novel anti-HIV macrocyclic peptide from Palicourea condensata. J Nat Prod. 2001;64:249-50.  Back to cited text no. 29
30.Rosengren KJ, Daly NL, Plan MR, Waine C, Craik DJ. Twists, knots, and rings in proteins. Structural definition of the cyclotide framework. J Biol Chem 2003;278:8606-16.  Back to cited text no. 30
31.Koltay A, Daly NL, Gustafson KR, Craik DJ. Structure of circulin B and implications for antimicrobial activity of cyclotides. Int J Pept Res Ther 2005;11:99-106.  Back to cited text no. 31
32.Saska I, Gillon AD, Hatsugai N, Dietzgen RG, Ikuko H, Anderson MA, et al. An asparaginyl endopeptidase mediates in vivo protein backbone cyclization. J Biol Chem 2007;282:29721-8.  Back to cited text no. 32
33.Simonsen SM, Sando L, Ireland DC, Colgrave ML, Bharathi R, Göransson U, et al. A continent of plant defense peptide diversity: cyclotides in Australian Hybanthus (Violaceae). Plant Cell 2005;17:3176-89.  Back to cited text no. 33
34.Plan MRR, Göransson U, Clark RJ, Daly NL, Colgrave ML, Craik DJ. The cyclotide fingerprint in Oldenlandia affinis: elucidation of chemically modified, linear and novel macrocyclic peptides. Chembiochem 2007;8:1001-11.  Back to cited text no. 34
35.Gunasekera S, Foley FM, Clark RJ, Sando L, Fabri LJ, Craik D, et al. Engineering stabilized vascular endothelial growth factor-A antagonists: synthesis, structural characterization and bioactivity of grafted analogues of cyclotides. J Med Chem 2008;51:7697-704.  Back to cited text no. 35
36.Tam JP, Yi-An L, Jin-Long Y, Kou-Wei C. An unusual structural motif of antimicrobial peptides containing end-to-end macrocycle and cystine-knot disulfides. Proc Natl Acad Sci U S A 1999;96:8913-8.  Back to cited text no. 36
37.Jennings C, West J, Waine C, Craik D, Anderson M. Biosynthesis and insecticidal properties of plant cyclotides: The cyclic knotted proteins from Oldenlandia affinis. Proc Natl Acad Sci U S A 2001;98:10614-9.  Back to cited text no. 37
38.Jennings C, Rosengren KJ, Daly NL, Plan M, Stevens J, Scanlon MJ, et al. Isolation, solution structure, and insecticidal activity of kalata B2, a circular protein with a twist: do Möbius strips exist in nature? Biochemistry 2005;44:851-60.  Back to cited text no. 38
39.Colgrave ML, Kotze AC, Ireland DC, Wang CK, Craik DJ. The antihelmintic activity of cyclotides: natural variants with enhanced activity. Chembiochem 2008a;9:1939-45.  Back to cited text no. 39
40.Colgrave ML, Kotze AC, Huang YH, O'Grady J, Simonsen SM, Craik DJ. Cyclotides: natural, circular plant peptides that possess significant activity against gastrointestinal nematode parasites of sheep. Biochemistry 2008b;47:5581-9.  Back to cited text no. 40
41.Colgrave ML, Kotze AC, Knopp S, McCathy JS, Coleman GT, Craik DJ. Anthelmintic activity of cyclotides: In vitro studies with canine and human hookworms. Acta Trop 2009;109:163-6.  Back to cited text no. 41
42.Colgrave ML, Yen-Hua H, Craik DJ, Kotze AC. Cyclotide interactions with the nematode external surface. Antimicrob Agents Chemother 2010;54:2160-6.  Back to cited text no. 42
43.Göransson U, Sjögren M, Svangård E, Claeson P, Bohlin L. Reversible antifouling effect of the cyclotide cycloviolacin O2 against barnacles. J Nat Prod 2004;67:1287-90.  Back to cited text no. 43
44.Plan MR, Saska I, Caguan AG, Craik DJ. Backbone cyclized peptides from plants show molluscicidal activity against the rice pest Pomacea canaliculata (golden apple snail). J Agric Food Chem 2008;56:5237-41.  Back to cited text no. 44
45.Lindholm P, Göransson U, Johansson S, Claeson P, Gullbo J, Larrson R, et al. Cyclotides: a novel type of cytotoxic agents. Mol Cancer Ther 2002;1:365-9.  Back to cited text no. 45
46.Svangård E, Göransson U, Hocaoglu Z, Gullbo J, Larsson R, Claeson P, Bohlin L. Cytotoxic cyclotides from Viola tricolor. J Nat Prod 2004;67:144-7.  Back to cited text no. 46
47.Svangård E. Cytotoxic cyclotides: structure, activity, and mode of action. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy. Acta Universitatis. 19. 2005.  Back to cited text no. 47
48.Herrmann A, Svangård E, Claeson P, Gullbo J, Bohlin L, Göransson U. Key role of glutamic acid for the cytotoxic activity of the cyclotide cycloviolacin O2. Cell Mol Life Sci 2006;63:235-45.  Back to cited text no. 48
49.Herrmann A, Burman B, Mylne JS, Karlsson G, Gullbo J, Craik DJ et al. The alpine violet, Viola biflora, is a rich source of cyclotides with potent cytotoxicity. Phytochemistry. 2008;69:939-52.  Back to cited text no. 49
50.Gerlach SL. Characterization and bioactivity of cyclotides from Psychotria leptothyrsa (Rubiaceae). Ann Arbor (MI); UMI ProQuest Dissertation Publishing; 2010.  Back to cited text no. 50
51.Gerlach SL, Burman R, Bohlin L, Mondal D, Göransson U. Isolation, characterization and bioactivity of novel cyclotides from the Micronesian plant, Psychotria leptothyrsa var. longicarpa. J Nat Prod 2010a;73:1207-13.  Back to cited text no. 51
52.Gerlach SL, Rathinakumar R, Chakravarty G, Göransson U, Wimley WC, Darwin SP et al. Anticancer and chemosensitizing abilities of Cycloviolacin O2 from Viola odorata and Psyle cyclotides from Psychotria leptothyrsa. Biopolymers 2010b;94:617-25.  Back to cited text no. 52
53.Tang J, Wang CK, Xulin P, He Y, Guangzhi Z, Wenyan X, et al. Isolation and characterization of cytotoxic cyclotides from Viola tricolor. Peptides 2010a;31:1434-40.  Back to cited text no. 53
54.Tang J, Wang CK, Pan X, Yan H, Zeng G, Wenyan X, et al. Isolation and characterization of bioactive cyclotides from Viola labridorica. Helvetica Chemica Acta 2010b;93:2287-95.  Back to cited text no. 54
55.Wenjun H, Chan LY, Zeng G, Daly NL, Craik DJ, Tan N. Isolation and characterization of cytotoxic cyclotides from Viola philippica. Peptides 2011;32:1719-1723.  Back to cited text no. 55
56.Yeshak MY, Burman R, Asres K, Göransson U. Cyclotides from an extreme habitat: characterization of cyclic peptides from Viola abyssinica of the Ethiopian Highlands. J Nat Prod 2011;74:727-31.  Back to cited text no. 56
57.Pränting M, Lööv C, Burman R, Göransson U, Andersson DI. The cyclotide cycloviolacin O2 from Viola odorata has potent bactericidal activity against Gram-negative bacteria. J Antimicrob Chemother 2010;65:1964-71.  Back to cited text no. 57
58.Nguyen GKT, Zhang S, Wang W, Wong CTT, Nguyen NTK, Tam JP. Discovery of a linear cyclotide from the bracelet subfamily and its disulfide mapping by Top-down mass spectrometry. J Biol Chem 2011;286:44833-44.  Back to cited text no. 58
59.Barbeta BL, Marshall AT, Gillon AD, Craik DJ, Anderson AA. Plant cyclotides disrupt epithelial cells in the midgut of lepidopteran larvae. Proc Natl Acad Sci U S A 2008;105:1221-5.  Back to cited text no. 59
60.Broussalis AM, Göransson U, Coussio JD, Ferraro G, Martino P, Claeson P. First cyclotide from Hybanthus (Violaceae). Phytochemistry 2001;58:47-51.  Back to cited text no. 60
61.Pinto MF, Fensterseifer IC, Migliolo L, Sousa DA, de Capdville G, Arboleda-Valencia JW, et al. Identification and structural characterization of novel cyclotide with activity against an insect pest of sugar cane. J Biol Chem 2012;287:134-47.  Back to cited text no. 61
62.Gustafson KR, Walton LK, Sowder II RC, Johnson DG, Pannell LK, Cardellina JH, et al. New circulin macrocyclic polypeptides from Chassalia parvifolia. J Nat Prod 2000;63:176-8.  Back to cited text no. 62
63.Hallock YF, Sowder II RC, Pannell LK, Hughes CB, Johnson DG, Gulakowski R, et al. Cycloviolins A-D, anti-HIV macrocyclic peptides from Leonia cymosa. J Org Chem 2000;65:124-8.  Back to cited text no. 63
64.Ireland DC, Wang CKL, Wilson JA, Gustafson KR, Craik DJ. Cyclotides as natural anti-HIV agents. Biopolymers 2007;90:51-60.  Back to cited text no. 64
65.Wang CK, Colgrave ML, Gustafson KR, Ireland DC, Göransson U, Craik DJ. Anti-HIV cyclotides from the Chinese medicinal herb Viola yedoensis. J Nat Prod 2007;71:47-52.  Back to cited text no. 65
66.Daly NL, Gustafson KR, Craik DJ. The role of the cyclic peptide backbone in the anti-HIV activity of the cyclotide kalata B1. FEBS Lett 2004;574:69-72.  Back to cited text no. 66
67.Daly NL, Clark RJ, Craik DJ. Kalata B8, a novel antiviral circular protein, exhibits conformational flexibility in the cystine knot motif. Biochem J 2006;393:619-26.  Back to cited text no. 67
68.Chen B, Colgrave ML, Daly NL, Rosengren KJ, Gustafson KR, Craik DJ. Isolation and characterization of novel cyclotides from Viola hederacea: solution structure and anti-HIV activity of vhl-1, a leaf-specific expressed cyclotide. J Biol Chem 2005;280:22395-405.  Back to cited text no. 68
69.Kamimori H, Hall K, Craik DJ, Aguilar M. Studies on the membrane interactions of the cyclotides kalata B1 and kalata B6 on model membrane systems by surface plasmon resonance. Anal Biochem 2005;337:149-53.  Back to cited text no. 69
70.Svangård E, Burman R, Gunasekera S, Lövborg H, Gullbo J, Göransson U. Mechanism of action of cytotoxic cyclotides: cycloviolacin O2 disrupts lipid membranes. J Nat Prod 2007;70:643-7.  Back to cited text no. 70
71.Henriques ST, Huang YH, Rosengren KJ, Franquelim HG, Carvalho FA, Johnson A, et al. Decoding the membrane activity of the cyclotide kalata B1: the importance of phosphatidylethanolamine phospholipids and lipid organization on hemolytic and anti-HIV activites. J Biol Chem 2011;286:24231-41.  Back to cited text no. 71
72.Burman R, Strömstedt AA, Malmsten M, Göransson U. Cyclotide-membrane interactions: Defining factors of membrane binding, depletion and disruption. Biochim Biophys Acta 2011b;1808:2665-73.  Back to cited text no. 72
73.Sando L, Henriques ST, Foley F, Simonsen SM, Daly NL, Hall KN, et al. A synthetic mirror image kalata B1 reveals that cyclotide activity is independent of a protein receptor. Chembiochem 2011;12:2456-62.  Back to cited text no. 73
74.Shenkarev ZO, Nadezdin KD, Lyukmanova EN, Sobol VA, Skjeldal L, Arseniev AS. Divalent cation coordination and mode of membrane interaction in cyclotides: NMR spatial structure of ternary complex Kalata B7/M 2+ /DPC micelle. J Inorg Biochem 2008;102:1246-56.  Back to cited text no. 74
75.Burman R, Herrmann A, Tran R, Kivelä J-E, Lomize A, Gullbo J, Göransson U. Cytotoxic potency of small macrocyclic knot proteins: Structure-activity and mechanistic studies of native and chemically modified cyclotides. Org Biomol Chem 2011a;9:4306-14.  Back to cited text no. 75
76.Huang Y, Colgrave M, Daly N, Kelshian A, Martinac B, Craik DJ. The biological activity of the prototypic cyclotides kalata B1 is modulated by the formation of multimeric pores. J Biol Chem 2009;284:20699-707.  Back to cited text no. 76
77.Ireland DC, Colgrave ML, Craik DJ. A novel suite of cyclotides from Viola odorata: sequence variation and the implications for structure, function and stability. Biochem J 2006a;400:1-12.  Back to cited text no. 77
78.Ireland DC, Colgrave ML, Nguyencong P, Daly NL, Craik DJ. Discovery and characterization of a linear cyclotides from Viola odorata: implications for the processing of circular proteins. J Mol Biol 2006b;357:1522-35.  Back to cited text no. 78
79.Dutton JL, Renda RF, Waine C, Clark RJ, Daly NL, Jennings CV, Anderson MA, Craik DJ. Conserved structural and sequence elements implicated in the processing of gene-encoded circular proteins. J Biol Chem 2004;279:46858-67.  Back to cited text no. 79
80.Colgrave ML, Craik DJ. Thermal, chemical, and enzymatic stability of the cyclotides kalata B1: the importance of the cyclic cystine knot. Biochemistry 2004;43:5965-75.  Back to cited text no. 80
81.Göransson U, Svangård E, Claeson P, Bohlin L. Novel strategies for isolation and characterization of cyclotides: the discovery of bioactive macrocyclic plant peptides in Violaceae. Curr Protein Pept Sci 2004;5:317-29.  Back to cited text no. 81


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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]

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