The Tarantula Toxins ProTx-II and Huwentoxin-IV Differentially Interact with Human Na_v1.7 Voltage Sensors to Inhibit Channel Activation and Inactivation

Abstract

The voltage-gated sodium channel Na v

Analysis of the Structural and Molecular Basis of Voltage-sensitive Sodium Channel Inhibition by the Spider Toxin Huwentoxin-IV (μ-TRTX-Hh2a)

“…8b reveals residues lending marked differences in affinity toward the channel subtypes. This face of the molecule illustrates the contrast between Nav1.2 and Nav1.7 when mutating three basic residues, Lys 18 , Arg 26 , and Lys 27 . HwTX-IV affinity for Nav1.7 is much less sensitive to mutations at these positions than Nav1.2.…”

“…These observations underscore the importance of Trp 30 and Lys 32 and suggest that these residues may be a universal determinant of sodium channel activity in these toxin families. Phe 6 , Lys 18 , Arg 26 , and Lys 27 appear to make isoform-specific interactions. These novel findings may provide a basis for the rational design of toxin-based peptides with improved VGSC potency and/or selectivity.…”

“…Although all property types exist in the interface, it is primarily basic residues located on loops 3 and 4 that confer selectivity between Nav1.2 and Nav1.7. Basicity at the Lys 18 , Arg 26 , and Lys 27 positions appears to be a requirement for affinity toward Nav1.2. It is unclear where on the channel the selectivity interface interacts, but acidic residues located on the DII S3-S4 linker of Nav1.7 along with residues in the pore domain of DIII may be implicated.…”

“…S4 was manually moved down into a resting state configuration, the S1-S2 and S3-S4 loops were regenerated, and the entire model was energy-minimized. Native HwTX-IV was manually docked into the Nav1.7 homology model based on the results of the alanine scan of HwTX-IV inhibition against Nav1.7 and on published Nav1.7 mutations that affect HwTX-IV binding (8,18,19). Following the manual docking, the entire Nav1.7 DII S1-S4 with docked HwTX-IV system was minimized, and an implicit membrane molecular dynamics simulation was performed using the CHARMm force field with Generalized Born Implicit Membrane (Discovery Studio (36)) to further refine the docked structure.…”

“…However, very little is known about the channel residues involved in these interactions. The only studies addressing this question are from Cummins and colleagues (8,18,19), who have identified several residues in the S3-S4 linker region of domain II that are crucial for huwentoxin-IV inhibition of Nav1.7. Even less is known about the toxin residues that interact with VGSCs.…”