title: The new kappa-KTx 2.5 from the scorpion Opisthacanthus cayaporum.
abstract: The kappa-KTx family of peptides, which is the newest K⁺-channel blocker family from scorpion venom, is present in scorpions from the families Scorpionidae and Liochelidae. Differently from the other scorpion KTx families, the three-dimensional structure of the known kappa-KTxs toxins is formed by two parallel α-helices linked by two disulfide bridges. Here, the characterization of a new kappa-KTx peptide, designated kappa-KTx 2.5, derived from the Liochelidae scorpion Opisthacanthus cayaporum, is described. This peptide was purified by HPLC and found to be identical to OcyC8, a predicted mature sequence precursor (UniProtKB C5J89) previously described by our group. The peptide was chemically synthesized and the circular dichroism (CD) spectra of both, native and synthetic, conducted at different temperatures in water and water/trifluoroethanol (TFE), showed a predominance of α-helices. The kappa-KTx 2.5 is heat stable and was shown to be a blocker of K⁺-currents on hKv1.1, and hKv1.4, with higher affinity for Kv1.4 channels (IC₅₀= 71 μM). Similarly to the other kappa-KTxs, the blockade of K⁺-channels occurred at micromolar concentrations, leading to uncertainness about their proper molecular target, and consequently their pharmacologic effect. In order to test other targets, kappa-KTx2.5 was tested on other K⁺-channels, on Na⁺-channels, on bacterial growth and on smooth muscle tissue, a known assay to identify possible bradykinin-potentiating peptides, due to the presence of two contiguous prolines at the C-terminal sequence. It has no effect on the targets used except on hKv1.1, and hKv1.4 expressed in Chinese hamster ovary cells. Since the only plausible function found for kappa-KTx2.5 seems to be the blockade of K⁺-channels, a discussion regarding the analysis of structure-function relationships is included in this communication, based on sequence alignments of members of the kappa-KTx toxin family, and on computational simulation of a structural model of the kappa-KTx2.5-Kv1.2 complex.
authors.affiliation: Laboratório de Toxinologia, Universidade de Brasília, Brasília, DF 70910-900, Brazil.
authors.forename: Thalita Soares
authors.initials: TS
authors.lastname: Camargos
authors.forename: Rita
authors.initials: R
authors.lastname: Restano-Cassulini
authors.forename: Lourival Domingos
authors.initials: LD
authors.lastname: Possani
authors.forename: Steve
authors.initials: S
authors.lastname: Peigneur
authors.forename: Jan
authors.initials: J
authors.lastname: Tytgat
authors.forename: Carlos Alberto
authors.initials: CA
authors.lastname: Schwartz
authors.forename: Erica Maria C
authors.initials: EM
authors.lastname: Alves
authors.forename: Sonia Maria
authors.initials: SM
authors.lastname: de Freitas
authors.forename: Elisabeth Ferroni
authors.initials: EF
authors.lastname: Schwartz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006224:Cricetinae; D003412:Cricetulus; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development; D005260:Female; D006168:Guinea Pigs; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D011498:Protein Precursors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D017433:Protein Structure, Secondary; D012604:Scorpion Venoms / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012605:Scorpions / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013211:Staphylococcus aureus / Q000187:drug effects / Q000254:growth & development; D013329:Structure-Activity Relationship; D014162:Transfection; D014981:Xenopus
chemical_list: D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011498:Protein Precursors; D012604:Scorpion Venoms