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Structural and functional differences of two toxins from the scorpion Pandinus imperator
K C Klenk1, T C Tenenholz, D R Matteson
1Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, USA.
Proteins
|March 9, 2000
Summary
Pandinotoxins PiTX-K alpha and PiTX-K beta are scorpion toxins that target potassium channels. Structural differences explain why PiTX-K beta binds less effectively to dorsal root ganglia neurons than PiTX-K alpha.
Area of Science:
- Biochemistry
- Neuroscience
- Structural Biology
Background:
- Pandinotoxins (PiTX-K alpha and PiTX-K beta) are Charybdotoxin family members.
- These scorpion toxins are utilized to characterize potassium (K+) channels.
Purpose of the Study:
- To elucidate the structural basis for the 800-fold difference in affinity between PiTX-K alpha and PiTX-K beta for K+ channels.
- To understand the functional impact of a single amino acid substitution (P10E) on toxin-channel interactions.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy to determine the 3D structure of PiTX-K beta.
- Comparison of PiTX-K beta structure with the known structure of PiTX-K alpha.
- Physiological assays to measure toxin-channel binding affinities.
Main Results:
- Structural analysis revealed differences between PiTX-K alpha and PiTX-K beta at critical residues (K27) and the mutation site (P10E).
- In PiTX-K beta, the E10 residue's negative charge can interact with K27, reducing the positive charge in that region.
- PiTX-K beta exhibits an 800-fold lower affinity (IC50 = 6,500 nM) for K+ channels in dorsal root ganglia (DRG) neurons compared to PiTX-K alpha (IC50 = 8.0 nM).
Conclusions:
- The structural differences, particularly the proximity of E10 to K27 in PiTX-K beta, explain its reduced binding affinity for K+ channels.
- This study highlights the importance of specific amino acid residues and their electrostatic interactions in determining the potency of scorpion toxins on ion channels.