Cytotoxic cyclotides from Viola tricolor.
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.
Svangård
Erika
E
Division of Pharmacognosy, Department of Medicinal Chemistry, Uppsala University, Biomedical Centre, Uppsala, Sweden.
Göransson
Ulf
U
Hocaoglu
Zozan
Z
Gullbo
Joachim
J
Larsson
Rolf
R
Claeson
Per
P
Bohlin
Lars
L
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D045744:Cell Line, Tumor; D004354:Drug Screening Assays, Antitumor; D005858:Germany; D006801:Humans; D020128:Inhibitory Concentration 50; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D010946:Plants, Medicinal / Q000737:chemistry*; D013329:Structure-Activity Relationship; D032413:Viola / Q000737:chemistry*
D000596:Amino Acids; D010456:Peptides, Cyclic; D010940:Plant Proteins