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Updated: May 24, 2026
Measuring Nucleotide Binding to Intact, Functional Membrane Proteins in Real Time
Published on: March 11, 2021
Looking over toxin-K(+) channel interactions. Clues from the structural and functional characterization of α-KTx
Eliana G Stehling1, Mauricio L Sforça, Nilson I T Zanchin
1Department of Toxicological and Bromatologic Clinical Analyses, Faculty of Pharmaceutical Sciences of Ribeirão Preto, USP, Ribeirão Preto, Brazil.
Abstract:
α-KTx toxin Tc32, from the Amazonian scorpion Tityus cambridgei, lacks the dyad motif, including Lys27, characteristic of the family and generally associated with channel blockage. The toxin has been cloned and expressed for the first time. Electrophysiological experiments, by showing that the recombinant form blocks Kv1.3 channels of olfactory bulb periglomerular cells like the natural Tc32 toxin, when tested on the Kv1.3 channel of human T lymphocytes, confirmed it is in an active fold. The nuclear magnetic resonance-derived structure revealed it exhibits an α/β scaffold typical of the members of the α-KTx family. TdK2 and TdK3, all belonging to the same α-KTx 18 subfamily, share significant sequence identity with Tc32 but diverse selectivity and affinity for Kv1.3 and Kv1.1 channels. To gain insight into the structural features that may justify those differences, we used the recombinant Tc32 nuclear magnetic resonance-derived structure to model the other two toxins, for which no experimental structure is available. Their interaction with Kv1.3 and Kv1.1 has been investigated by means of docking simulations. The results suggest that differences in the electrostatic features of the toxins and channels, in their contact surfaces, and in their total dipole moment orientations govern the affinity and selectivity of toxins. In addition, we found that, regardless of whether the dyad motif is present, it is always a Lys side chain that physically blocks the channels, irrespective of its position in the toxin sequence.
Insights
The α-KTx toxin Tc32, lacking a key motif, effectively blocks Kv1.3 channels. Structural and simulation studies reveal that toxin-channel electrostatic interactions, not just specific motifs, determine binding affinity and selectivity.
Area of Science:
- Biochemistry
- Structural Biology
- Neuroscience
Background:
- Alpha-KTx toxins are peptides known to block ion channels.
- The α-KTx 18 subfamily includes toxins with varying channel selectivity.
- Toxin Tc32 from Tityus cambridgei lacks the characteristic dyad motif.
Purpose of the Study:
- To characterize the structure and function of α-KTx toxin Tc32.
- To investigate the structural basis for differential channel selectivity among related α-KTx toxins.
- To understand the role of specific structural features in ion channel blockade.
Main Methods:
- Toxin cloning and recombinant expression.
- Electrophysiological recordings to assess channel block.
- Nuclear magnetic resonance (NMR) spectroscopy for structure determination.
- Molecular modeling and docking simulations.
Main Results:
- Recombinant Tc32 toxin functionally blocks Kv1.3 channels.
- NMR structure reveals Tc32 possesses a typical α/β scaffold.
- Modeling and simulations suggest electrostatic interactions and dipole moments dictate toxin-channel affinity and selectivity.
- Lysine side chains, irrespective of the dyad motif, are responsible for channel physical blockade.
Conclusions:
- Tc32 is a functional Kv1.3 channel blocker despite lacking the canonical dyad motif.
- Structural and electrostatic factors, rather than a specific motif, govern α-KTx toxin selectivity.
- A lysine residue's position and surrounding electrostatic environment are critical for channel blockade.
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