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The Journal of Membrane Biology

, Volume 179, Issue 1, pp 13–25 | Cite as

Effects of Toxins Pi2 and Pi3 on Human T Lymphocyte Kv1.3 Channels: The Role of Glu7 and Lys24

  • M.  Péter Jr.
  • Z.  Varga
  • P.  Hajdu
  • R.  Gáspár Jr.
  • S.  Damjanovich
  • E.  Horjales
  • L.D.  Possani
  • G.  Panyi

Abstract.

Pandinus imperator scorpion toxins Pi2 and Pi3 differ only by a single amino acid residue (neutral Pro7 in Pi2 vs. acidic Glu7 in Pi3). The binding kinetics of these toxins to human Kv1.3 showed that the decreased on rate (k ON = 2.18 × 108 m −1sec−1 for Pi2 and 1.28 × 107 m −1sec−1 for Pi3) was almost entirely responsible for the increased dissociation constant (K d ) of Pi3 (K d = 795 pm) as compared to Pi2 (K d = 44 pm). The ionic strength dependence of the association rates was exactly the same for the two toxins indicating that through-space electrostatic interactions can not account for the different on rates. Results were further analyzed on the basis of the three-dimensional structural models of the toxins. A 3D structure of Pi3 was generated from the NMR spectroscopy coordinates of Pi2 by computer modeling. The Pi3 model resulted in a salt bridge between Glu7 and Lys24 in Pi3. Based on this finding our interpretation of the reduced on rate of Pi3 is that the intramolecular salt bridge reduces the local positive electrostatic potential around Lys24 resulting in decreased short-range electrostatic interactions during the binding step. To support our finding, we constructed a 3D model of the Ser-10-Asp Charybdotoxin mutant displaying distinctly reduced affinity for Shaker channels. The mutant Charybdotoxin structure also displayed a salt bridge between residues Asp10 and Lys27 equivalent to the one between Glu7 and Lys24 in Pi3.

Key Words: Human lymphocyte — Kv1.3 — Scorpion toxin binding —Pandinus imperator— Charybdotoxin — Three-dimensional structure — Salt bridge 

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Copyright information

© Springer-Verlag New York Inc. 2001

Authors and Affiliations

  • M.  Péter Jr.
    • 1
  • Z.  Varga
    • 1
  • P.  Hajdu
    • 1
  • R.  Gáspár Jr.
    • 1
  • S.  Damjanovich
    • 1
  • E.  Horjales
    • 2
  • L.D.  Possani
    • 2
  • G.  Panyi
    • 1
  1. 1.Department of Biophysics and Cell Biology, University Medical School of Debrecen, 4012 Hungary, POB 39HU
  2. 2.Department of Molecular Recognition and Structural Biology, Institute of Biotechnology, National Autonomous University of Mexico, Avenida Universidad, 2001 Cuernavaca 62210 MEXICOMX

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