Disulfide bridge reorganization induced by proline mutations in maurotoxin
E Carlier1, Z Fajloun, P Mansuelle
1Laboratoire de Neurobiologie des Canaux Ioniques, INSERM U464, IFR Jean Roche, Marseille, France.
Abstract:
Maurotoxin (MTX) is a 34-residue toxin that has been isolated from the venom of the chactidae scorpion Scorpio maurus palmatus, and characterized. Together with Pi1 and HsTx1, MTX belongs to a family of short-chain four-disulfide-bridged scorpion toxins acting on potassium channels. However, contrary to other members of this family, MTX exhibits an uncommon disulfide bridge organization of the type C1-C5, C2-C6, C3-C4 and C7-C8, versus C1-C5, C2-C6, C3-C7 and C4-C8 for both Pi1 and HsTx1. Here, we report that the substitution of MTX proline residues located at positions 12 and/or 20, adjacent to C3 (Cys(13)) and C4 (Cys(19)), results in conventional Pi1- and HsTx1-like arrangement of the half-cystine pairings. In this case, this novel disulfide bridge arrangement is without obvious incidence on the overall three-dimensional structure of the toxin. Pharmacological assays of this structural analog, [A(12),A(20)]MTX, reveal that the blocking activities on Shaker B and rat Kv1.2 channels remain potent whereas the peptide becomes inactive on rat Kv1.3. These data indicate, for the first time, that discrete point mutations in MTX can result in a marked reorganization of the half-cystine pairings, accompanied with a novel pharmacological profile for the analog.
Insights
Maurotoxin (MTX), a scorpion toxin, has an unusual disulfide bridge structure. Point mutations in MTX can alter this structure, leading to changes in its activity on potassium channels.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- Maurotoxin (MTX) is a scorpion toxin from Scorpio maurus palmatus.
- MTX belongs to a family of toxins acting on potassium channels.
- MTX possesses a unique disulfide bridge arrangement compared to related toxins like Pi1 and HsTx1.
Purpose of the Study:
- To investigate the effect of specific proline residue substitutions in MTX.
- To determine if these substitutions alter the disulfide bridge organization.
- To evaluate the impact on MTX's pharmacological activity on potassium channels.
Main Methods:
- Site-directed mutagenesis was used to substitute proline residues at positions 12 and/or 20 in MTX.
- The disulfide bridge pairings of the resulting analog ([A(12),A(20)]MTX) were analyzed.
- Pharmacological assays were performed on Shaker B, rat Kv1.2, and rat Kv1.3 channels.
Main Results:
- Substitution of proline residues resulted in a conventional disulfide bridge arrangement, similar to Pi1 and HsTx1.
- The overall three-dimensional structure of the MTX analog remained largely unchanged.
- [A(12),A(20)]MTX retained potent blocking activity on Shaker B and rat Kv1.2 channels.
- The MTX analog became inactive on rat Kv1.3 channels.
Conclusions:
- Discrete point mutations in MTX can induce significant reorganization of disulfide bridge pairings.
- These structural changes are associated with a distinct pharmacological profile.
- MTX analogs offer a valuable tool for understanding structure-activity relationships in potassium channel toxins.
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