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- Svangård, Erika, 1975-
(författare)
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Cytotoxic Cyclotides : Structure, Activity, and Mode of Action
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cyclotides are small cyclic plant proteins, and this thesis addresses their cytotoxic structure-activity properties and their mode of action on human cancer cell lines. Cyclotides were isolated from Viola odorata and Viola tricolor; three novel cyclotide sequences and two known sequences, but of new origin, were identified using mass spectrometry, amino acid analysis, and Edman degradation. The cyclotide structure includes three disulphide bonds in a knotted arrangement, which forces hydrophobic amino acid residues to be exposed on the surface of the molecule; 3-D homology models of cyclotides have revealed an amphipathic surface and charged residues located at similar positions in the molecules. The charged amino acid residues were shown to play a key role in the cytotoxicity of the cyclotide cycloviolacinO2 on a human lymphoma cell line. Methylation of Glu caused a dramatic change in cytotoxicity, lowering the potency 48 times, whereas concealing the charge of Arg with 1,2-cyclohexanedione caused virtually no change in potency. Acetylation of the two Lys caused a 3-fold reduction in potency, and masking all positive charges caused a 7-fold reduction. Additionally, disturbing the amphipathic structure by reducing and alkylating the disulphide bonds abolished the cytotoxicity. The time dependency of cytotoxicity and cell gross morphology after cyclotide exposure were investigated on the lymphoma cell line. Cells exposed to 4 µM of cycloviolacinO2 showed necrotic characteristics, such as membrane disintegration, within 5 min; a membrane disruptive effect of cycloviolacinO2 was also observed in a functional assay based on liposomes at a peptide-to-lipid molar ratio of 6.5. The anti-tumour properties of cycloviolacinO2 were evaluated on three human cancer cell lines using the hollow fibre assay in vitro and in vivo. The cyclotide exhibited potent anti-tumour activity in the micro-molar concentration range on all cell lines in vitro, but no effect on tumour growth could be established in vivo.
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- Svangård, Erika, et al.
(författare)
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Cytotoxic cyclotides from Viola tricolor
- 2004
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Ingår i: Journal of natural products (Print). - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 67:2, s. 144-7
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Tidskriftsartikel (refereegranskat)abstract
- A crude fraction of Viola tricolor rich in small lipophilic proteins was prepared and subjected to fractionation guided by bioactivity, using RP-HPLC and a fluorometric cytotoxicity assay. Two human cancer cell lines, U-937 GTB (lymphoma) and RPMI-8226/s (myeloma), were used in this study. The most potent compounds isolated, that is, the compounds showing the lowest IC(50) values, were shown to be three small proteins: vitri A (IC(50) = 0.6 microM and IC(50) = 1 microM, respectively), varv A (IC(50) = 6 microM and IC(50) = 3 microM, respectively), and varv E (IC(50) = 4 microM in both cell lines). Their sequences, determined by automated Edman degradation, quantitative amino acid analysis, and mass spectrometry, were cyclo-GESCVWIPCITSAIGCSCKSKVCYRNGIPC (vitri A), cyclo-GETCVGGTCNTPGCSCSWPVCTRNGLPVC (varv A), and cyclo-GETCVGGTCNTPGCSCSWPVCTRNGLPIC (varv E), of which vitri A is described for the first time. Each forms a head-to-tail cyclic backbone, with six cysteine residues being involved in three disulfide bonds, characteristic of the family of small proteins called the cyclotides. This is the first report on cyclotides from the species V. tricolor and the first report on the sequence of the cytotoxic cyclotide vitri A.
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- Svangård, Erika, et al.
(författare)
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Mechanism of action of cytotoxic cyclotides : cycloviolacin O2 disrupts lipid membranes
- 2007
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Ingår i: Journal of natural products (Print). - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 70:4, s. 643-647
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Tidskriftsartikel (refereegranskat)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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- Svangård, Erika, et al.
(författare)
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Primary and 3-D modelled structures of two cyclotides from Viola odorata
- 2003
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Ingår i: Phytochemistry. - 0031-9422 .- 1873-3700. ; 64:1, s. 135-142
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Tidskriftsartikel (refereegranskat)abstract
- Two polypeptides named vodo M and vodo N, both of 29 amino acids, have been isolated from Viola odorata L. (Violaceae) using ion exchange chromatography and reversed phase HPLC. The sequences were determined by automated Edman degradation, quantitative amino acid analysis, and mass spectrometry (MS). Using MS, it was established that vodo M (cyclo-SWPVCTRNGAPICGESCFTGKCYTVQCSC) and vodo N (cyclo-SWPVCYRNGLPVCGETCTLGKCYTAGCSC) form a head-to-tail cyclic backbone and that six cysteine residues are involved in three disulphide bonds. Their origin, sequences, and cyclic nature suggest that these peptides belong to the family of cyclic plant peptides, called cyclotides. The three-dimensional structures of vodo M and vodo N were modelled by homology, using the experimentally determined structure of the cyclotide kalata B1 as the template. The images of vodo M and vodo N show amphipathic structures with considerable surface hydrophobicity for a protein modelled in a polar environment.
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- Trabi, Manuela, et al.
(författare)
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Variations in cyclotide expression in viola species
- 2004
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Ingår i: Journal of natural products (Print). - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 67:5, s. 806-10
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Tidskriftsartikel (refereegranskat)
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