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Thongyoo P, Roqué-Rosell N, Leatherbarrow RJ, Tate EW. Chemical and biomimetic total syntheses of natural and engineered MCoTI cyclotides. Org Biomol Chem 2008; 6:1462-70. [DOI: 10.1039/b801667d] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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102
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Abstract
Cyclotides are disulfide rich macrocyclic plant peptides that are defined by their unique topology in which a head-to-tail cyclized backbone is knotted by the interlocking arrangement of three disulfide bonds. This cyclic cystine knot motif gives the cyclotides exceptional resistance to thermal, chemical, or enzymatic degradation. Over 100 cyclotides have been reported and display a variety of biological activities, including a cytoprotective effect against HIV infected cells. It has been hypothesized that cyclotides from one subfamily, the Möbius subfamily, may be more appropriate than bracelet cyclotides as drug candidates given their lower toxicity to uninfected cells. Here, we report the anti-HIV and cytotoxic effects of three cyclotides, including two from the Möbius subfamily. We show that Möbius cyclotides have comparable inhibitory activity against HIV infection to bracelet cyclotides and that they are generally less cytotoxic to the target cells. To explore the structure activity relationships (SARs) of the 29 cyclotides tested so far for anti-HIV activity, we modeled the structures of the 21 cyclotides whose structures have not been previously solved. We show that within cyclotide subfamilies there is a correlation between hydrophobicity of certain loop regions and HIV inhibition. We also show that charged residues in these loops impact on the activity of the cyclotides, presumably by modulating membrane binding. In addition to providing new SAR data, this report is a mini-review that collates all cyclotide anti-HIV information reported so far and provides a resource for future studies on the therapeutic potential of cyclotides as natural anti-HIV agents.
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Affiliation(s)
- David C. Ireland
- Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, QLD 4072, Australia
- UQ Business School. University of Queensland, Brisbane, QLD 4072, Australia
| | - Conan K. L. Wang
- Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, QLD 4072, Australia
| | - Kirk R. Gustafson
- Molecular Targets Development Program, Center for Cancer Research, National Cancer Institute, Building 562, Room 201, Frederick, Maryland 21702-1201
| | - David J. Craik
- Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, QLD 4072, Australia
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103
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Wang CKL, Colgrave ML, Gustafson KR, Ireland DC, Goransson U, Craik DJ. Anti-HIV cyclotides from the Chinese medicinal herb Viola yedoensis. JOURNAL OF NATURAL PRODUCTS 2008; 71:47-52. [PMID: 18081258 PMCID: PMC6327322 DOI: 10.1021/np070393g] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Cyclotides are macrocyclic plant peptides characterized by a knotted arrangement of three disulfide bonds. They display a range of interesting bioactivities, including anti-HIV and insecticidal activities. More than 100 different cyclotides have been isolated from two phylogenetically distant plant families, the Rubiaceae and Violaceae. In this study we have characterized the cyclotides from Viola yedoensis, an important Chinese herb from the Violaceae family that has been reported to contain potential anti-HIV agents. From V. yedoensis five new and three known cyclotides were identified and shown to have anti-HIV activity. The most active of these is cycloviolacin Y5, which is one of the most potent of all cyclotides tested so far using in vitro XTT-based anti-HIV assays. Cycloviolacin Y5 is the most hydrophobic of the cyclotides from V. yedoensis. We show that there is a positive correlation between the hydrophobicity and the anti-HIV activity of the new cyclotides and that this trend tracks with their ability to disrupt membranes, as judged from hemolytic assays on human erythrocytes.
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Affiliation(s)
| | | | | | | | | | - David J. Craik
- To whom correspondence should be addressed. Tel: 61-7-3346-2019. Fax: 61-7-3346-2029.
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104
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Thongyoo P, Jaulent AM, Tate EW, Leatherbarrow RJ. Immobilized protease-assisted synthesis of engineered cysteine-knot microproteins. Chembiochem 2007; 8:1107-9. [PMID: 17526063 DOI: 10.1002/cbic.200700187] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Panumart Thongyoo
- Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AZ, UK
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105
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Svangård E, Burman R, Gunasekera S, Lövborg H, Gullbo J, Göransson U. Mechanism of action of cytotoxic cyclotides: cycloviolacin O2 disrupts lipid membranes. JOURNAL OF NATURAL PRODUCTS 2007; 70:643-7. [PMID: 17378610 DOI: 10.1021/np070007v] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
In recent years, the cyclotides have emerged as the largest family of naturally cyclized proteins. Cyclotides display potent cytotoxic activity that varies with the structure of the proteins, and combined with their unique structure, they represent novel cytotoxic agents. However, their mechanism of action is yet unknown. In this work we show that disruption of cell membranes plays a crucial role in the cytotoxic effect of the cyclotide cycloviolacin O2 (1), which has been isolated from Viola odorata. Cell viability and morphology studies on the human lymphoma cell line U-937 GTB showed that cells exposed to 1 displayed disintegrated cell membranes within 5 min. Functional studies on calcein-loaded HeLa cells and on liposomes showed rapid concentration-dependent release of their respective internal contents. The present results show that cyclotides have specific membrane-disrupting activity.
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Affiliation(s)
- Erika Svangård
- Division of Pharmacognosy, Department of Medicinal Chemistry, Biomedical Centre, Uppsala University, Uppsala, Sweden
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106
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Gruber CW, Cemazar M, Anderson MA, Craik DJ. Insecticidal plant cyclotides and related cystine knot toxins. Toxicon 2007; 49:561-75. [PMID: 17224167 DOI: 10.1016/j.toxicon.2006.11.018] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Accepted: 11/17/2006] [Indexed: 10/23/2022]
Abstract
Cyclotides are small disulphide-rich peptides found in plants from the violet (Violaceae), coffee (Rubiaceae) and cucurbit (Cucurbitaceae) families. They have the distinguishing structural features of a macrocyclic peptide backbone and a cystine knot made up of six conserved cysteine residues, which makes cyclotides exceptionally stable. Individual plants express a suite of cyclotides in a wide range of tissue types, including leaves, flowers, stems and roots and it is thought that their natural function in plants is as defence agents. This proposal is supported by their high expression levels in plants and their toxic and growth retardant activity in feeding trials against Helicoverpa spp. insect pests. This review describes the structures and activities of cyclotides with specific reference to their insecticidal activity and compares them with structurally similar cystine knot proteins from peas (Pisum sativum) and an amaranthus crop plant (Amaranthus hypocondriancus). More broadly, cystine knot proteins are common in a wide range of organisms from fungi to mammals, and it appears that this interesting structural motif has evolved independently in different organisms as a stable protein framework that has a variety of biological functions.
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Affiliation(s)
- Christian W Gruber
- Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, Queensland, 4072, Australia
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107
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Abstract
In many countries today, the number of students selecting chemistry for higher studies is decreasing. At the same time, interest in the environmental aspects of chemistry, green chemistry, and sustainable use of natural products is increasing among the young generation of students. By modernizing and renewing a venerable proven science, pharmacognosy would have a strategic position to connect biology and chemistry. This multidisciplinary subject is important for discovery of novel and unique molecules with drug potential, and for revealing unknown targets, by studying evolutionary structure-activity optimization in nature. In this paper, the overall aim and strategies of our research are presented and exemplified by three different research projects.Natural products are involved in scientific issues important for a sustainable society, and a multidisciplinary subject such as pharmacognosy can, therefore, be useful in increasing future interest in both chemistry and biology.
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108
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Craik DJ, Daly NL. NMR as a tool for elucidating the structures of circular and knotted proteins. MOLECULAR BIOSYSTEMS 2007; 3:257-65. [PMID: 17372654 DOI: 10.1039/b616856f] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cyclotides are a recently discovered family of mini-proteins that have a head-to-tail cyclised backbone stabilized by a knotted arrangement of three disulfide bonds. They have a wide range of biological activities, including uterotonic, anti-bacterial, anti-HIV, and anti-tumour activity but their insecticidal activities suggest that their natural function is in plant defense. They are exceptionally resistant to chemical, enzymatic and thermal treatments because of their unique structural scaffold. This stability and resistance to proteolysis makes them a potentially valuable protein engineering tool at the interface of chemistry and biology: they have the structure of proteins but the stability and biophysical properties of organic molecules. In this review the role of NMR in defining the structures of cyclotides is described.
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Affiliation(s)
- David J Craik
- Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane QLD 4072, Australia.
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109
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Ireland D, Colgrave M, Craik D. A novel suite of cyclotides from Viola odorata: sequence variation and the implications for structure, function and stability. Biochem J 2006; 400:1-12. [PMID: 16872274 PMCID: PMC1635437 DOI: 10.1042/bj20060627] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Cyclotides are a fascinating family of plant-derived peptides characterized by their head-to-tail cyclized backbone and knotted arrangement of three disulfide bonds. This conserved structural architecture, termed the CCK (cyclic cystine knot), is responsible for their exceptional resistance to thermal, chemical and enzymatic degradation. Cyclotides have a variety of biological activities, but their insecticidal activities suggest that their primary function is in plant defence. In the present study, we determined the cyclotide content of the sweet violet Viola odorata, a member of the Violaceae family. We identified 30 cyclotides from the aerial parts and roots of this plant, 13 of which are novel sequences. The new sequences provide information about the natural diversity of cyclotides and the role of particular residues in defining structure and function. As many of the biological activities of cyclotides appear to be associated with membrane interactions, we used haemolytic activity as a marker of bioactivity for a selection of the new cyclotides. The new cyclotides were tested for their ability to resist proteolysis by a range of enzymes and, in common with other cyclotides, were completely resistant to trypsin, pepsin and thermolysin. The results show that while biological activity varies with the sequence, the proteolytic stability of the framework does not, and appears to be an inherent feature of the cyclotide framework. The structure of one of the new cyclotides, cycloviolacin O14, was determined and shown to contain the CCK motif. This study confirms that cyclotides may be regarded as a natural combinatorial template that displays a variety of peptide epitopes most likely targeted to a range of plant pests and pathogens.
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Affiliation(s)
- David C. Ireland
- *Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, The University of Queensland, Brisbane QLD 4072, Australia
- †School of Business, University of Queensland, Brisbane, QLD 4072, Australia
| | - Michelle L. Colgrave
- *Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, The University of Queensland, Brisbane QLD 4072, Australia
| | - David J. Craik
- *Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, The University of Queensland, Brisbane QLD 4072, Australia
- To whom correspondence should be addressed (email )
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110
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Ireland DC, Colgrave ML, Nguyencong P, Daly NL, Craik DJ. Discovery and Characterization of a Linear Cyclotide from Viola odorata: Implications for the Processing of Circular Proteins. J Mol Biol 2006; 357:1522-35. [PMID: 16488428 DOI: 10.1016/j.jmb.2006.01.051] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 01/11/2006] [Accepted: 01/12/2006] [Indexed: 10/25/2022]
Abstract
Cyclotides are mini-proteins of 28-37 amino acid residues that have the unusual feature of a head-to-tail cyclic backbone surrounding a cystine knot. This molecular architecture gives the cyclotides heightened resistance to thermal, chemical and enzymatic degradation and has prompted investigations into their use as scaffolds in peptide therapeutics. There are now more than 80 reported cyclotide sequences from plants in the families Rubiaceae, Violaceae and Cucurbitaceae, with a wide variety of biological activities observed. However, potentially limiting the development of cyclotide-based therapeutics is a lack of understanding of the mechanism by which these peptides are cyclized in vivo. Until now, no linear versions of cyclotides have been reported, limiting our understanding of the cyclization mechanism. This study reports the discovery of a naturally occurring linear cyclotide, violacin A, from the plant Viola odorata and discusses the implications for in vivo cyclization of peptides. The elucidation of the cDNA clone of violacin A revealed a point mutation that introduces a stop codon, which inhibits the translation of a key Asn residue that is thought to be required for cyclization. The three-dimensional solution structure of violacin A was determined and found to adopt the cystine knot fold of native cyclotides. Enzymatic stability assays on violacin A indicate that despite an increase in the flexibility of the structure relative to cyclic counterparts, the cystine knot preserves the overall stability of the molecule.
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Affiliation(s)
- David C Ireland
- Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, Qld 4072, Australia
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111
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Factors Influencing the Stability of Cyclotides: Proteins with a Circular Backbone and Cystine Knot Motif. Int J Pept Res Ther 2006. [DOI: 10.1007/s10989-006-9019-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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112
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Affiliation(s)
- David J Craik
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
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113
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114
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Abstract
CyBase is a curated database and information source for backbone-cyclized proteins. The database incorporates naturally occurring cyclic proteins as well as synthetic derivatives, grafted analogues and acyclic permutants. The database provides a centralized repository of information on all aspects of cyclic protein biology and addresses issues pertaining to the management and searching of topologically circular sequences. The database is freely available at .
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Affiliation(s)
| | | | - David J. Craik
- To whom correspondence should be addressed. Tel: +61 7 3346 2019; Fax: +61 7 3346 2029;
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115
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Craik DJ, Cemazar M, Wang CKL, Daly NL. The cyclotide family of circular miniproteins: Nature's combinatorial peptide template. Biopolymers 2006; 84:250-66. [PMID: 16440288 DOI: 10.1002/bip.20451] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The cyclotides are a recently discovered family of miniproteins that contain a head-to-tail cyclized backbone and a knotted arrangement of disulfide bonds. They are approximately 30 amino acids in size and are present in high abundance in plants from the Violaceae, Rubiaceae, and Cucurbitaceae families, with individual plants containing a suite of up to 100 cyclotides. They have a diverse range of biological activities, including uterotonic, anti-HIV, antitumor, and antimicrobial activities, although their natural function is likely that of defending their host plants from pathogens and pests. This review focuses on the structural aspects of cyclotides, which may be thought of as a natural combinatorial peptide template in which a wide range of amino acids is displayed on a compact molecular core made up of the cyclic cystine knot structural motif. Cyclotides are exceptionally stable and are resistant to denaturation via thermal, chemical, or enzymatic treatments. The structural features that contribute to their remarkable stability are described in this review.
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Affiliation(s)
- David J Craik
- Institute for Molecular Bioscience and Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane.
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116
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Chen B, Colgrave ML, Wang C, Craik DJ. Cycloviolacin H4, a hydrophobic cyclotide from Viola hederaceae. JOURNAL OF NATURAL PRODUCTS 2006; 69:23-8. [PMID: 16441062 DOI: 10.1021/np050317i] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Cycloviolacin H4, a new macrocyclic miniprotein comprising 30 amino acid residues, was isolated from the underground parts of the Australian native violet Viola hederaceae. Its sequence, cyclo-(CAESCVWIPCTVTALLGCSCSNNVCYNGIP), was determined by nanospray tandem mass spectrometry and quantitative amino acid analysis. A knotted disulfide arrangement, which was designated as a cyclic cystine knot motif and characteristic to all known cyclotides, is proposed for stabilizing the molecular structure and folding. The cyclotide is classified in the bracelet subfamily of cyclotides due to the absence of a cis-Pro peptide bond in the circular peptide backbone. A model of its three-dimensional structure was derived based on the template of the homologous cyclotide vhr1 (Trabi et al. Plant Cell 2004, 16, 2204-2216). Cycloviolacin H4 exhibits the most potent hemolytic activity in cyclotides reported so far, and this activity correlates with the size of a surface-exposed hydrophobic patch. This work has thus provided insight into the factors that modulate the cytotoxic properties of cyclotides.
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Affiliation(s)
- Bin Chen
- Institute for Molecular Bioscience, Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, QLD 4072, Australia
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117
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Simonsen SM, Sando L, Ireland DC, Colgrave ML, Bharathi R, Göransson U, Craik DJ. A continent of plant defense peptide diversity: cyclotides in Australian Hybanthus (Violaceae). THE PLANT CELL 2005; 17:3176-89. [PMID: 16199617 PMCID: PMC1276036 DOI: 10.1105/tpc.105.034678] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Cyclotides are plant-derived miniproteins that have the unusual features of a head-to-tail cyclized peptide backbone and a knotted arrangement of disulfide bonds. It had been postulated that they might be an especially large family of host defense agents, but this had not yet been tested by field data on cyclotide variation in wild plant populations. In this study, we sampled Australian Hybanthus (Violaceae) to gain an insight into the level of variation within populations, within species, and between species. A wealth of cyclotide diversity was discovered: at least 246 new cyclotides are present in the 11 species sampled, and 26 novel sequences were characterized. A new approach to the discovery of cyclotide sequences was developed based on the identification of a conserved sequence within a signal sequence in cyclotide precursors. The number of cyclotides in the Violaceae is now estimated to be >9000. Cyclotide physicochemical profiles were shown to be a useful taxonomic feature that reflected species and their morphological relationships. The novel sequences provided substantial insight into the tolerance of the cystine knot framework in cyclotides to amino acid substitutions and will facilitate protein engineering applications of this framework.
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Affiliation(s)
- Shane M Simonsen
- Institute for Molecular Bioscience, University of Queensland, Australian Research Council Special Research Centre for Functional and Applied Genomics, Brisbane 4072, Australia
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118
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Chen B, Colgrave ML, Daly NL, Rosengren KJ, Gustafson KR, Craik DJ. Isolation and Characterization of Novel Cyclotides from Viola hederaceae. J Biol Chem 2005; 280:22395-405. [PMID: 15824119 DOI: 10.1074/jbc.m501737200] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Based on a newly established sequencing strategy featured by its efficiency, simplicity, and easy manipulation, the sequences of four novel cyclotides (macrocyclic knotted proteins) isolated from an Australian plant Viola hederaceae were determined. The three-dimensional solution structure of V. hederaceae leaf cyclotide-1 (vhl-1), a leaf-specific expressed 31-residue cyclotide, has been determined using two-dimensional (1)H NMR spectroscopy. vhl-1 adopts a compact and well defined structure including a distorted triple-stranded beta-sheet, a short 3(10) helical segment and several turns. It is stabilized by three disulfide bonds, which, together with backbone segments, form a cyclic cystine knot motif. The three-disulfide bonds are almost completely buried into the protein core, and the six cysteines contribute only 3.8% to the molecular surface. A pH titration experiment revealed that the folding of vhl-1 shows little pH dependence and allowed the pK(a) of 3.0 for Glu(3) and approximately 5.0 for Glu(14) to be determined. Met(7) was found to be oxidized in the native form, consistent with the fact that its side chain protrudes into the solvent, occupying 7.5% of the molecular surface. vhl-1 shows anti-HIV activity with an EC(50) value of 0.87 microm.
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Affiliation(s)
- Bin Chen
- Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD 4072, Australia
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119
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Avrutina O, Schmoldt HU, Gabrijelcic-Geiger D, Le Nguyen D, Sommerhoff CP, Diederichsen U, Kolmar H. Trypsin inhibition by macrocyclic and open-chain variants of the squash inhibitor MCoTI-II. Biol Chem 2005; 386:1301-6. [PMID: 16336125 DOI: 10.1515/bc.2005.148] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
MCoTI-I and MCoTI-II from the seeds of Momordica cochinchinensis are inhibitors of trypsin-like proteases and the only known members of the large family of squash inhibitors that are cyclic and contain an additional loop connecting the amino- and the carboxy-terminus. To investigate the contribution of macrocycle formation to biological activity, we synthesized a set of open-chain variants of MCoTI-II that lack the cyclization loop and contain various natural and non-natural amino acid substitutions in the reactive-site loop. Upon replacement of P1 lysine residue #10 within the open-chain variant of MCoTI-II by the non-natural isosteric nucleo amino acid AlaG [beta-(guanin-9-yl)-L-alanine], a conformationally restricted arginine mimetic, residual inhibitory activity was detected, albeit reduced by four orders of magnitude. While the cyclic inhibitors MCoTI-I and MCoTI-II were found to be very potent trypsin inhibitors, with picomolar inhibition constants, the open-chain variants displayed an approximately 10-fold lower affinity. These data suggest that the formation of a circular backbone in the MCoTI squash inhibitors results in enhanced affinity and therefore is a determinant of biological activity.
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Affiliation(s)
- Olga Avrutina
- Institute for Organic and Biomolecular Chemistry, Georg-August-University, D-37077 Göttingen, Germany
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