RESUMEN
AIM: To study the antitumor peptide components in the stems and leaves of mistletoe (Viscum coloratum (Kom.) Nakai), the primary structure of the novel peptide was elucidated. METHODS: Cation exchange, gel filtration and HPLC were employed for isolation and purification. Matrix Assisted Laser Desorption Ionization-Time of Flight-Mass Spectrometry was used to determine the mass. The complete amino acid sequence of the novel peptide was obtained by Edman degradation combined with enzyme digestion. The antitumor activity of the peptide in vitro was studied with MTT method. RESULTS: The primary stucture of the peptide named as viscotoxin B2 is KSCCKNTTGRNIYNTCRFAGGSRERCAKLSGCKIISASTCPSDYPK. The IC50 value of viscotoxin B2 on the Rat Osteoblast-like Sarcoma 17/2.8 cells in vitro is 1.6 mg x L(-1). CONCLUSION: Viscotoxin B2 in V. coloratum, which has high similarity with viscotoxins from V. album, showed antitumor activity.
Asunto(s)
Antineoplásicos Fitogénicos/aislamiento & purificación , Péptidos/química , Proteínas de Plantas/química , Proteínas de Plantas/farmacología , Plantas Medicinales/química , Viscum/química , Secuencia de Aminoácidos , Animales , Antineoplásicos Fitogénicos/química , Antineoplásicos Fitogénicos/farmacología , Neoplasias Óseas/patología , Concentración 50 Inhibidora , Datos de Secuencia Molecular , Peso Molecular , Osteosarcoma/patología , Péptidos/aislamiento & purificación , Péptidos/farmacología , Hojas de la Planta/química , Proteínas de Plantas/aislamiento & purificación , Tallos de la Planta/química , Ratas , Células Tumorales Cultivadas/efectos de los fármacosRESUMEN
A novel conotoxin, kappa-conotoxin (kappa-BtX), has been purified and characterized from the venom of a worm-hunting cone snail, Conus betulinus. The toxin, with four disulfide bonds, shares no sequence homology with any other conotoxins. Based on a partial amino acid sequence, its cDNA was cloned and sequenced. The deduced sequence consists of a 26-residue putative signal peptide, a 31-residue mature toxin, and a 13-residue extra peptide at the C terminus. The extra peptide is cleaved off by proteinase post-processing. All three Glu residues are gamma-carboxylated, one of the two Pro residues is hydroxylated at position 27, and its C-terminal residue is Pro-amidated. The monoisotopic mass of the toxin is 3569.0 Da. Electrophysiological experiments show that: 1) among voltage-gated channels, kappa-BtX is a specific modulator of K(+) channels; 2) among the K channels, kappa-BtX specifically up-modulates the Ca(2+)- and voltage-sensitive BK channels (252 +/- 47%); 3) its EC(50) is 0.7 nm with a single binding site (Hill = 0.88); 4) the time constant of wash-out is 8.3 s; and 5) kappa-BtX has no effect on single channel conductance, but increases the open probability of BK channels. It is concluded that kappa-BtX is a novel specific biotoxin against BK channels.