A Subfamily of Acidic α-K+ Toxins*
- Isabelle Huys‡§,
- Timoteo Olamendi-Portugal¶,
- Blanca Ines Garcia-Gómez¶,
- Isabel Vandenberghe∥,
- Jozef Van Beeumen∥,
- Karin Dyason**,
- Elke Clynen§‡‡,
- Shunyi Zhu‡,
- Jurg van der Walt**,
- Lourival D. Possani¶ and
- Jan Tytgatत
- ‡Laboratory of Toxicology, University of Leuven, E. Van Evenstraat 4, 3000 Leuven, Belgium, ¶Department of Molecular Medicine and Bioprocesses, Institute of Biotechnology, Avenida Universidad, 2001, Cuernavaca, Mexico, ∥Laboratory of Protein Biochemistry and Protein Engineering, University of Gent, 9000 Gent, Belgium, **Department of Physiology, University of Potchefstroom, Potchefstroom, South Africa, and ‡‡Laboratory for Developmental Physiology and Molecular Biology, University of Leuven, Naamsestraat 59, 3000 Leuven, Belgium
- ↵§§ To whom correspondence should be addressed. Tel.: 32-16-32-34-03; Fax: 32-16-32-34-05; E-mail: Jan.Tytgat{at}pharm.kuleuven.ac.be.
Abstract
Three homologous acidic peptides have been isolated from the venom of three different Parabuthus scorpion species, P. transvaalicus, P. villosus, and P. granulatus. Analysis of the primary sequences reveals that they structurally belong to subfamily 11 of short chain α-K+-blocking peptides (Tytgat, J., Chandy, K. G., Garcia, M. L., Gutman, G. A., Martin-Eauclaire, M. F., van der Walt, J. J., and Possani, L. D. (1999) Trends Pharmacol. Sci. 20, 444–447). These toxins are 36–37 amino acids in length and have six aligned cysteine residues, but they differ substantially from the other α-K+ toxins because of the absence of the critical Lys27 and their total overall negative charge. Parabutoxin 1 (PBTx1), which has been expressed by recombinant methods, has been submitted to functional characterization. Despite the lack of the Lys27, this toxin blocks several Kv1-type channels heterologously expressed in Xenopus oocytes but with low affinities (micromolar range). Because a relationship between the biological activity and the acidic residue substitutions may exist, we set out to elucidate the relative impact of the acidic character of the toxin and the lack of the critical Lys27 on the weak activity of PBTx1 toward Kv1 channels. To achieve this, a specific mutant named rPBTx1 T24F/V26K was made recombinantly and fully characterized on Kv1-type channels heterologously expressed in Xenopus oocytes. Analysis of rPBTx1 T24F/V26K displaying an affinity toward Kv1.2 and Kv1.3 channels in the nanomolar range shows the importance of the functional dyad above the acidic character of this toxin.
- Received October 7, 2003.
- The American Society for Biochemistry and Molecular Biology, Inc.
