Analysis of the interacting surface of maurotoxin with the voltage-gated Shaker B K(+) channel
Ziad Fajloun1, Nicolas Andreotti, Mohamed Fathallah
1ERT 62, Faculté de Médecine Nord, 13916 Marseille Cedex 15, France. zfajloun@ul.edu.lb
Abstract:
Maurotoxin (MTX) is a 34-residue toxin that was isolated initially from the venom of the scorpion Scorpio maurus palmatus. Unlike the other toxins of the α-KTx6 family (Pi1, Pi4, Pi7, and HsTx1), MTX exhibits a unique disulfide bridge organization of the type C(1) C(5) , C(2) C(6) , C(3) C(4) , and C(7) C(8) (instead of the conventional C(1) C(5) , C(2) C(6) , C(3) C(7) , and C(4) C(8) , herein referred to as Pi1-like) that does not prevent its folding along the classic α/β scaffold of scorpion toxins. MTX(Pi1) is an MTX variant with a conventional pattern of disulfide bridging without any primary structure alteration of the toxin. Here, using MTX and/or MTX(Pi1) as models, we investigated how the type of folding influences toxin recognition of the Shaker B potassium channel. Amino acid residues of MTX that were studied for Shaker B recognition were selected on the basis of their homologous position in charybdotoxin, a three disulfide-bridged scorpion toxin also active on this channel type. These residues favored either an MTX- or MTX(Pi1) -like folding. Our data indicate clearly that Lys(23) and Tyr(32) (two out of ten amino acid residues studied) are the most important residues for Shaker B channel blockage by MTX. For activity on SKCa channels, the same amino acid residues also affect, directly or indirectly, the recognition of SK channels. The molecular modeling technique and computed docking indicate the existence of a correlation between the half cystine pairings of the mutated analogs and their activity on the Shaker B K(+) channel. Overall, mutations in MTX could, or could not, change the reorganization of disulfide bridges of this molecule without affecting its α/β scaffold. However, changing of the peptide backbone (cross linking disulfide bridges from MTX-like type vs MTX(Pi1) -like type) appears to have less impact on the molecule activity than mutation of certain key amino acids such as Lys(23) and Tyr(32) in this toxin.
Insights
Maurotoxin (MTX) and its variant MTX(Pi1) were studied to understand how disulfide bridge organization affects Shaker B potassium channel activity. Key residues Lys(23) and Tyr(32) are crucial for MTX
Area of Science:
- * Biochemistry and Molecular Biology
- * Neuroscience and Pharmacology
Background:
- * Maurotoxin (MTX), a scorpion-derived peptide, belongs to the α-KTx6 family and possesses a unique disulfide bridge organization.
- * This unique structure differs from the conventional Pi1-like disulfide bridging found in other related toxins.
- * MTX(Pi1) serves as a variant with conventional disulfide bridging, allowing for comparative studies on folding and channel interaction.
Purpose of the Study:
- * To investigate the impact of different disulfide bridge organizations on the functional activity of Maurotoxin (MTX).
- * To determine the role of specific amino acid residues in the recognition and blockage of the Shaker B potassium channel by MTX.
- * To explore the correlation between disulfide bridge patterns, molecular modeling, and channel activity.
Main Methods:
- * Comparative analysis of MTX and MTX(Pi1) using Shaker B potassium channel assays.
- * Site-directed mutagenesis of specific amino acid residues in MTX based on homology with charybdotoxin.
- * Molecular modeling and computed docking to analyze structural-activity relationships.
Main Results:
- * Lysine at position 23 (Lys(23)) and Tyrosine at position 32 (Tyr(32)) were identified as critical residues for Shaker B channel blockage by MTX.
- * These residues also influence the recognition of SKCa channels, indicating broader functional importance.
- * Mutations altering disulfide bridges did not significantly affect the α/β scaffold, but key residue mutations had a greater impact on activity.
Conclusions:
- * The specific disulfide bridge organization in MTX has a less pronounced effect on channel activity compared to mutations in key residues like Lys(23) and Tyr(32).
- * The folding pattern, influenced by disulfide bridges, impacts toxin recognition of potassium channels, but specific amino acid substitutions are more determinative of function.
- * Structural insights from molecular modeling correlate mutated analogs' half-cystine pairings with their activity on the Shaker B K(+) channel.
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