| 1. |
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| 2. |
- Weimann, C, et al.
(författare)
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Spasmolytic effects of baccharis conferta and some of its constituents
- 2002
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Ingår i: Journal of Pharmacy and Pharmacology (JPP). - : Oxford University Press (OUP). - 0022-3573 .- 2042-7158. ; 54:1, s. 99-104
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Tidskriftsartikel (refereegranskat)abstract
- The Nahua of the Mexican state of Veracruz use Baccharis conferta in the treatment of a variety of gastrointestinal illnesses, especially diarrhoea associated with gastrointestinal cramps. The aerial parts of B. conferta were investigated phytochemically and pharmacologically using the guinea pig ileum assay as a model (histamine, KCI and electric stimulation). The crude ethanolic extract showed a dose-dependent antispasmodic effect that was particularly strong in flavonoid-rich fractions (e.g. IC50 value for fraction E.3.1 from the ethyl acetate fraction, in histamine-induced contraction, 10 microg mL(-1)). Several flavonoids (apigenin-4',7-dimethylether, naringenin-4',7-dimethylether, pectolinarigenin and cirsimaritin) were isolated, while others were identified in complex fractions by GC-MS. The flavonoids play an important role in the antispasmodic activity of this indigenous drug. Additionally, oleanolic acid and its methyl ester as well as erythrodiol were isolated. Oleanolic acid methyl ester shows weak antibacterial activity against M. luteusand E. coli (20 microg/spot in a TLC assay). The phytochemical as well as the pharmacological data provide some in-vitro evidence forthe use of B. conferta in thetreatment of gastrointestinal cramps.
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| 3. |
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| 4. |
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| 5. |
- Broussalis, Adriana M., et al.
(författare)
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First cyclotide from Hybanthus (Violaceae)
- 2001
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Ingår i: Phytochemistry. - : Elsevier. - 0031-9422 .- 1873-3700. ; 58:1, s. 47-51
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Tidskriftsartikel (refereegranskat)abstract
- Hypa A, a novel macrocyclic polypeptide containing 30 amino acid residues, has been isolated from the n-butanol extract of the Argentine plant Hybanthus parviflorus. The sequence, cyclo-(SCVYIPCTITALLGCSCKNKVCYNGIPCAE), was determined by automated Edman degradation, quantitative amino acid analysis and nanospray MS/MS2. Three intramolecular disulfide bridges stabilize the cyclic peptide backbone of hypa A. Using these structural features to classify the peptide as a cyclotide, we extended the distribution of that substance class to a new genus, and now propose a uniform nomenclature for cyclotides.
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| 6. |
- Burman, Robert, 1979-, et al.
(författare)
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Evaluation of toxicity and anti-tumour activity of cycloviolacin O2 in mice.
- 2010
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Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 94:5, s. 626-634
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Tidskriftsartikel (refereegranskat)abstract
- Cycloviolacin O2 is a small cyclic cysteine-rich protein belonging to the group of plant proteins called cyclotides. This cyclotide has been previously shown to exert cytotoxic activity against a variety of human tumor cell lines as well as primary cultures of human tumor cells in vitro. This study is the first evaluation of its tolerability and antitumor activity in vivo. Maximal-tolerated doses were estimated to 1.5 mg/kg for single intravenous (i.v.) dosing and 0.5 mg/kg for daily repeated dosing, respectively. Two different in vivo methods were used: the hollow fiber method with single dosing (i.v. 1.0 mg/kg) and traditional xenografts with repeated dosing over 2 weeks (i.v. 0.5 mg/kg daily, 5 days a week). The human tumor cell lines used displayed dose-dependent in vitro sensitivity (including growth in hollow fibers to confirm passage of cycloviolacin O2 through the polyvinylidene fluoride fibers), with IC50 values in the micromolar range. Despite this sensitivity in vitro, no significant antitumor effects were detected in vivo, neither with single dosing in the hollow fiber method nor with repeated dosing in xenografts. In summary, the results indicate that antitumor effects are minor or absent at tolerable (sublethal) doses, and cycloviolacin O2 has a very abrupt in vivo toxicity profile, with lethality after single injection at 2 mg/kg, but no signs of discomfort to the animals at 1.5 mg/kg. Repeated dosing of 1 mg/kg gave a local-inflammatory reaction at the site of injection after 2–3 days; lower doses were without complications.
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| 7. |
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| 8. |
- Claeson, Dick
(författare)
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U-Pb zircon age of metagranite with relict phenocryst texture at Linavare, map sheet 27K Nattavaara, Norbotten county
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Norrbotten, Sweden is a key area of Europe for future exploration and mining. To establish age relations for magmatic activity and metamorphic overprinting in this area, the sampled rock was selected (Fig. 1, 2, 21). This rock occurs at Linavare as mega-xenoliths of strongly deformed, foliated, recrystallised and low-radiation metagranite in massive subvolcanic granite to rhyolite porphyry that was age determined to 1870 ± 6 Ma, giving a lower age of the high-grade metamorphic event (this issue). The age of the regional metamorphic event may be deduced from the age of these two rocks, occurring between their igneous crystallisation ages. Determine the magmatic age of the metagranite is the main aim and if the zircon display metamorphic rims or overgrowths, these should be studied too.
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| 9. |
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| 10. |
- Claeson, Per, et al.
(författare)
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Calcium Antagonistic Properties of the Sesquiterpene T‐Cadinol : A Comparison with Nimodipine in the Isolated Rat Aorta
- 1991
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Ingår i: Pharmacology and Toxicology. - : Wiley. - 0901-9928 .- 1600-0773. ; 69:3, s. 173-177
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: (+)‐T‐Cadinol is a sesquiterpene with smooth muscle relaxing properties. In the isolated rat aorta, T‐cadinol relaxed contractions induced by 60 mM K+ in a concentration‐dependent fashion. The dihydropyridine calcium antagonist nimodipine was approximately 4,000 times more potent than T‐cadinol. While both drugs nearly abolished the K+‐induced contractions, they only partially relaxed contractions induced by phenylephrine. The relaxation induced by T‐cadinol and nimodipine in K+‐contracted aortic rings, was completely reversed by the calcium channel activator Bay K8644. In aortic preparations partially depolarized by 20 mM K+, Bay K8644 induced a concentration‐dependent contraction. Nimodipine shifted the Bay K8644 concentration‐response curve to the right in a parallel manner, consistent with a competitive mode of inhibition. T‐cadinol at concentrations less than 10−3.5 M also produced a right‐ward shift of the Bay K8644 concentration‐response curve with a maintained maximum response. However, the highest T‐cadinol concentration used (10−3.5 M) significantly reduced the maximum response. In conclusion, although T‐cadinol and nimodipine display marked structural differences, their pharmacological profiles of action have several features in common, suggesting that T‐cadinol is a calcium antagonist, possibly interacting with the dihydropyridine binding sites on the calcium channels. 1991 Nordic Pharmacological Society
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| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Göransson, Ulf, et al.
(författare)
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Expression of Viola cyclotides by liquid chromatography-mass spectrometry and tandem mass spectrometry sequencing of intercysteine loops after introduction of charges and cleavage sites by aminoethylation
- 2003
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Ingår i: Analytical Biochemistry. - 0003-2697 .- 1096-0309. ; 318:1, s. 107-117
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Tidskriftsartikel (refereegranskat)abstract
- The expression of cyclotides—macrocyclic plant peptides—was profiled in six violets, Viola cotyledon, V. biflora, V. arvensis,V. tricolor, V. riviniana, and V. odorata, by LC-MS. All were found to express notably complex mixtures, with single speciescontaining >50 cyclotides. To facilitate their sequencing by MS-MS, an analytical strategy is presented involving aminoethylation ofcysteines. This overcomes a number of problems intimately associated with the cyclotide core structure—that is, their joined N and Ctermini, disulfide knot, and low or clustered content of positively charged amino acids and enzymatic cleavage sites. As a result,charges as well as cleavage sites are introduced at the most conserved part of their sequence, the cysteines. Combined with trypticdigestion, all intercysteine loops are then of suitable size and charge for MS-MS sequencing. The utility of this strategy is shown bythe sequencing of two novel cyclotides isolated from V. cotyledon; vico A (cyclo-(AESCVYIPCFTGIAGCSCKNKVCYYNGSIPC)) and vico B(cyclo-(AESCVYIPCITGIAGCSCKNKVCYYNGSIPC)); their complete sequence could be determined bynanospray MS-MS. The strategy for converting conserved cysteines to enzymatic cleavage sites might also benefit the study of otherpeptides and proteins displaying similar structural problems for MS analysis.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Göransson, Ulf, et al.
(författare)
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Seven novel macrocyclic polypeptides from Viola arvensis
- 1999
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Ingår i: Journal of natural products (Print). - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 62:2, s. 283-286
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Tidskriftsartikel (refereegranskat)abstract
- Seven novel macrocyclic polypeptides, designated as varv peptides B-H, have been isolated from the aerial parts of Viola arvensis. Their primary structures have been elucidated by automated Edman degradation and mass spectrometry. They all consist of 29 or 30 amino acid residues, covalently cyclized via the amide backbone and by three internal disulfide bridges. Their amino acid sequences are as follows: varv peptide B, cyclo-(TCFGGTCNTPGCSCDPWPMCSRNGLPVCGE); varv peptide C, cyclo-(TCVGGTCNTPGCSCSWPVCTRNGVPICGE); varv peptide D, cyclo-(TCVGGSCNTPGCSCSWPVCTRNGLPICGE); varv peptide E, cyclo-(TCVGGTCNTPGCSCSWPVCTRNGLPICGE); varv peptide F, cyclo-(TCTLGTCYTAGCSCSWPVCTRNGVPICGE); varv peptide G, cyclo-(TCFGGTCNTPGCSCDPWPVCSRNGVPVCGE); and varv peptide H, cyclo-(TCFGGTCNTPGCSCETWPVCSRNGLPVCGE). The varv peptides B-H exhibited high degrees of homology with the hitherto known macrocyclic peptides varv peptide A, kalata B1, violapeptide I, circulins A and B, and cyclopsychotride A.
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| 21. |
- Herrmann, Anders, et al.
(författare)
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Key role of glutamic acid for the cytotoxic activity of the cyclotide cycloviolacin O2
- 2006
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Ingår i: Cellular and Molecular Life Sciences (CMLS). - : Springer Science and Business Media LLC. - 1420-682X .- 1420-9071. ; 63:2, s. 235-245
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Tidskriftsartikel (refereegranskat)abstract
- Cyclotides are cyclic plant proteins with potent cytotoxic effects. Here we systematically probed the importance of surface-exposed charged amino acid residues of the cyclotide cycloviolacin O2, using a strategy involving chemical modifications. We show that the single glutamic acid plays a key role for the cytotoxicity: methylation of this residue produced a 48-fold decrease in potency. Virtually no change in potency was observed when masking the single arginine residue using 1,2-cyclohexanedione, while acetylation of the two lysine residues reduced the potency 3-fold. The derivative with modifications at both arginine and lysine residues showed a 7-fold loss of potency. In addition, we show that the activity is dependent on an intact disulfide network and that the short sequences between the six cysteine residues, that is, the backbone loops, are devoid of cytotoxic activity.
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| 22. |
- Johansson, Senia, et al.
(författare)
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A neutrophil multitarget functional bioassay to detect anti-inflammatory natural products
- 2002
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Ingår i: Journal of natural products (Print). - : American Chemical Society (ACS). - 0163-3864 .- 1520-6025. ; 65:1, s. 32-41
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Tidskriftsartikel (refereegranskat)abstract
- A multitarget functional bioassay was optimized as a method for detecting substances interacting with the inflammatory process of activated neutrophil granulocytes, mainly to release elastase detected by p-nitroanilide (pNA) formation. Using this bioassay, 100 fractionated extracts of 96 plants were screened, with results presented in a manner that links recorded biological activity to phylogenetic information. The plants were selected to represent a major part of the angiosperms, with emphasis on medicinal plants, Swedish anti-inflammatory plants, and plants known to contain peptides. Of the tested extracts, 41% inhibited pNA formation more than 60%, and 3% stimulated formation. The extract of Digitalbis purpurea enhanced pNA formation, and digitoxin, the active compound, was isolated and identified. Plant extracts that exhibited potent nonselective inhibition (> 80% inhibition) were evaluated further for direct inhibition of isolated elastase and trypsin enzyme. The inhibitory effect of most tested extracts on the isolated enzyme elastase was similar to that of PAF- and fMLP-induced pNA formation. Compared to trypsin, inhibition of elastase by extracts of Rubus idaeus and Tabernaemontana dichotoma was significantly higher (80% and 99%, respectively). Inhibition of trypsin by the extract of Reseda luteola was high 97%. Orders such as Lamiales and Brassicales were shown to include a comparably high proportion of plants with inhibitory extracts.
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| 23. |
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| 24. |
- Johansson, Senia, et al.
(författare)
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Cytotoxicity of digitoxin and related cardiac glycosides in human tumor cells
- 2001
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Ingår i: Anti-Cancer Drugs. - 0959-4973 .- 1473-5741. ; 12:5, s. 475-83
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Tidskriftsartikel (refereegranskat)abstract
- The saponin digitonin, the aglycone digitoxigenin and five cardiac glycosides were evaluated for cytotoxicity using primary cultures of tumor cells from patients and a human cell line panel (representing different cytotoxic drug-resistance patterns). Of these seven compounds, proscillaridin A was the most potent (IC(50): 6.4--76 nM), followed by digitoxin, and then ouabain, digoxin, lanatoside C, digitoxigenin and digitonin. Correlation analysis of the log IC(50) values for the cell lines in the panel showed that compound cytotoxicity was only slightly influenced by resistance mechanisms that involved P-glycoprotein, topoisomerase II, multidrug resistance-associated protein and glutathione-mediated drug resistance. Digitoxin and digoxin expressed selective toxicity against solid tumor cells from patients, while proscillaridin A expressed no selective toxicity against either solid or hematological tumor cells. The results revealed marked differences in cytotoxicity between the cardiac glycosides, both in potency and selectivity, and modes of action for cytotoxicity that differ from that of commonly used anticancer drugs.
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| 25. |
- Johansson, S., et al.
(författare)
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Small, novel proteins from the mistletoe Phoradendron tomentosum exhibit highly selective cytotoxicity to human breast cancer cells
- 2003
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Ingår i: Cellular and Molecular Life Sciences (CMLS). - : Springer Science and Business Media LLC. - 1420-682X .- 1420-9071. ; 60:1, s. 165-175
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Tidskriftsartikel (refereegranskat)abstract
- Four novel proteins (phoratoxins C-F) have been isolated from the North American mistletoe Phoradendron tomentosum. The amino acid sequences of these phoratoxins were determined unambiguously using a combination of Edman degradation and trypsin enzymatic digestion, and by electrospray ionization tandem mass spectrometry sequencing. Phoratoxins C, E and F consist of 46 amino acid residues; and phoratoxin D of 41. All proteins had six cysteines, similar to the earlier described phoratoxins A and B, which are thionins. The cytotoxicity of each protein was evaluated in a human cell line panel that represented several cytotoxic drug-resistance mechanisms. For the half-maximal inhibitory concentrations (IC50 values) of the different cell lines in the panel, correlation with those of standard drugs was low. The most potent cytotoxic phoratoxin C was further tested on primary cultures of human tumor cells from patients. The solid tumor samples from breast cancer cells were 18 times more sensitive to phoratoxin C than the tested hematological tumor samples.
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| 26. |
- Li, Shi-Sheng, et al.
(författare)
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Ligatoxin B, a new cytotoxic protein with a novel helix-turn-helix DNA-binding domain from the mistletoe Phoradendron liga
- 2002
-
Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 366:Pt 2, s. 405-13
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Tidskriftsartikel (refereegranskat)abstract
- A new basic protein, designated ligatoxin B, containing 46 amino acid residues has been isolated from the mistletoe Phoradendron liga (Gill.) Eichl. (Viscaceae). The protein's primary structure, determined unambiguously using a combination of automated Edman degradation, trypsin enzymic digestion, and tandem MS analysis, was 1-KSCCPSTTAR-NIYNTCRLTG-ASRSVCASLS-GCKIISGSTC-DSGWNH-46. Ligatoxin B exhibited in vitro cytotoxic activities on the human lymphoma cell line U-937-GTB and the primary multidrug-resistant renal adenocarcinoma cell line ACHN, with IC50 values of 1.8 microM and 3.2 microM respectively. Sequence alignment with other thionins identified a new member of the class 3 thionins, ligatoxin B, which is similar to the earlier described ligatoxin A. As predicted by the method of homology modelling, ligatoxin B shares a three-dimensional structure with the viscotoxins and purothionins and so may have the same mode of cytotoxic action. The novel similarities observed by structural comparison of the helix-turn-helix (HTH) motifs of the thionins, including ligatoxin B, and the HTH DNA-binding proteins, led us to propose the working hypothesis that thionins represent a new group of DNA-binding proteins. This working hypothesis could be useful in further dissecting the molecular mechanisms of thionin cytotoxicity and of thionin opposition to multidrug resistance, and useful in clarifying the physiological function of thionins in plants.
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| 27. |
- Lindholm, Petra, et al.
(författare)
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Cyclotides : a novel type of cytotoxic agents
- 2002
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Ingår i: Molecular Cancer Therapeutics. - 1535-7163 .- 1538-8514. ; 1:6, s. 365-369
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Tidskriftsartikel (refereegranskat)abstract
- Cytotoxic activities of three naturally occurring macrocyclic peptides (cyclotides) isolated from the two violets, Viola arvensis Murr. and Viola odorata L., were investigated. A nonclonogenic fluorometric microculture assay was used to examine cytotoxicity in a panel of 10 human tumor cell lines representing defined types of cytotoxic drug resistance. Additionally, primary cultures of tumor cells from patients, and for comparison normal lymphocytes, were used to quantify cytotoxic activity. All three cyclotides, varv A, varv F, and cycloviolacin O2, exhibited strong cytotoxic activities, which varied in a dose-dependent manner. Cycloviolacin O2 was the most potent in all cell lines (IC50 0.1– 0.3 _M), followed by varv A (IC50 2.7–6.35 _M) and varv F (IC50 2.6 –7.4 _M), respectively. Activity profiles of the cyclotides differed significantly from those of antitumor drugs in clinical use, which may indicate a new mode of action. This, together with the exceptional chemical and biological stability of cyclotides, makes them interesting in particular for their potential as pharmacological tools and possibly as leads to antitumor agents.
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| 28. |
- Lindholm, Petra, et al.
(författare)
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Selective cytotoxicity evaluation in anticancer drug screening of fractionated plant extracts
- 2002
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Ingår i: Journal of Biomolecular Screening. - : Elsevier BV. - 1087-0571 .- 1552-454X. ; 7:4, s. 333-340
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Tidskriftsartikel (refereegranskat)abstract
- Chosen to reflect biodiversity in a phylogenetic sense, 100 fractionated plant extracts were screened in vitro for cytotoxicity following extraction and fractionation (polypeptide isolation). Of these 100 extracts, 30 were selected and then characterized preliminarily for antitumor potency and mode of action by testing them on two cell lines and primary cultures of human tumor cells. On the basis of cytotoxicity potency, 10 of the extracts were further characterized for anticancer activity in 10 human tumor cell lines. This final testing resulted in seven potential lead plants with superior evidence of antitumor potential: Colchicum autumnale L. (Colchicaceae), Digitalis lanata Ehrh. and Digitalis purpurea L. (Plantaginaceae), Helleborus cyclophyllus Boiss. (Ranunculaceae), Menyanthes trifoliata L. (Menyanthaceae), and Viola arvensis Murr. and Viola patrinii Ging. (Violaceae). Within a database of antitumor compounds, the activity profiles of the extracts from these seven plants were compared, by correlation analysis, with those of more than 100 other compounds, including 39 standard drugs from different classes of cytotoxic mechanisms. The activity profiles of six of these candidates were uncorrelated with those of the standard drugs, possibly indicating new pathways of drug-mediated cell death.
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| 29. |
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| 30. |
- 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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| 31. |
- 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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| 32. |
- 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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| 33. |
- 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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| 34. |
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| 35. |
- Wang, Conan, et al.
(författare)
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Combined X-ray and NMR analysis of the stability of the cyclotide cystine knot fold that underpins its insecticidal activity and potential use as a drug scaffold
- 2009
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 284:16, s. 10672-10683
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Tidskriftsartikel (refereegranskat)abstract
- Cyclotides are a family of plant defense proteins that are highly resistant to adverse chemical, thermal, and enzymatic treatment. Here, we present the first crystal structure of a cyclotide, varv F, from the European field pansy, Viola arvensis, determined at a resolution of 1.8 angstrom. The solution state NMR structure was also determined and, combined with measurements of biophysical parameters for several cyclotides, provided an insight into the structural features that account for the remarkable stability of the cyclotide family. The x-ray data confirm the cystine knot topology and the circular backbone, and delineate a conserved network of hydrogen bonds that contribute to the stability of the cyclotide fold. The structural role of a highly conserved Glu residue that has been shown to regulate cyclotide function was also determined, verifying its involvement in a stabilizing hydrogen bond network. We also demonstrate that varv F binds to dodecylphosphocholine micelles, defining the binding orientation and showing that its structure remains unchanged upon binding, further demonstrating that the cyclotide fold is rigid. This study provides a biological insight into the mechanism by which cyclotides maintain their native activity in the unfavorable environment of predator insect guts. It also provides a structural basis for explaining how a cluster of residues important for bioactivity may be involved in self-association interactions in membranes. As well as being important for their bioactivity, the structural rigidity of cyclotides makes them very suitable as a stable template for peptide-based drug design.
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