Fluorescent analogues of BeKm-1 with high and specific activity against the hERG channel

The scorpion toxin BeKm-1 blocks hERG cardiac potassium channels using an indispensable arginine residue

BeKm-1 is a peptide toxin from scorpion venom that blocks the pore of the potassium channel hERG (Kv11.1) in the human heart. Although individual protein structures have been resolved, the structure of the complex between hERG and BeKm-1 is unknown. Here, we used molecular dynamics and ensemble docking, guided by previous double-mutant cycle analysis data, to obtain an in silico model of the hERG-BeKm-1 complex. Adding to the previous mutagenesis study of BeKm-1, our model uncovers the key role of residue Arg20, which forms three interactions (a salt bridge and hydrogen bonds) with the channel vestibule simultaneously. Replacement of this residue even by lysine weakens the interactions significantly. In accordance, the recombinantly produced BeKm-1R20K mutant exhibited dramatically decreased activity on hERG. Our model may be useful for future drug design attempts.

Fluorescent- and tagged-protoxin II peptides: potent markers of the Nav 1.7 channel pain target

BACKGROUND AND PURPOSE

Protoxin II (ProTx II) is a high affinity gating modifier that is thought to selectively block the Na_v 1.7 voltage-dependent Na⁺ channel, a major therapeutic target for the control of pain. We aimed at producing ProTx II analogues entitled with novel functionalities for cell distribution studies and biochemical characterization of its Na_v channel targets.

EXPERIMENTAL APPROACH

We took advantage of the high affinity properties of the peptide, combined to its slow off rate, to design a number of new tagged analogues useful for imaging and biochemistry purposes. We used high-throughput automated patch-clamp to identify the analogues best matching the native properties of ProTx II and validated them on various Na_v -expressing cells in pull-down and cell distribution studies.

KEY RESULTS

Two of the produced ProTx II analogues, Biot-ProTx II and ATTO488-ProTx II, best emulate the pharmacological properties of unlabelled ProTx II, whereas other analogues remain high affinity blockers of Na_v 1.7. The biotinylated version of ProTx II efficiently works for the pull-down of several Na_v isoforms tested in a concentration-dependent manner, whereas the fluorescent ATTO488-ProTx II specifically labels the Na_v 1.7 channel over other Na_v isoforms tested in various experimental conditions.

CONCLUSIONS AND IMPLICATIONS

The properties of these ProTx II analogues as tools for Na_v channel purification and cell distribution studies pave the way for a better understanding of ProTx II channel receptors in pain and their pathophysiological implications in sensory neuronal processing. The new fluorescent ProTx II should also be useful in the design of new drug screening strategies.

Functional Impact of BeKm-1, a High-Affinity hERG Blocker, on Cardiomyocytes Derived from Human-Induced Pluripotent Stem Cells

I_Kr current, a major component of cardiac repolarization, is mediated by human Ether-à-go-go-Related Gene (hERG, K_v11.1) potassium channels. The blockage of these channels by pharmacological compounds is associated to drug-induced long QT syndrome (LQTS), which is a life-threatening disorder characterized by ventricular arrhythmias and defects in cardiac repolarization that can be illustrated using cardiomyocytes derived from human-induced pluripotent stem cells (hiPS-CMs). This study was meant to assess the modification in hiPS-CMs excitability and contractile properties by BeKm-1, a natural scorpion venom peptide that selectively interacts with the extracellular face of hERG, by opposition to reference compounds that act onto the intracellular face. Using an automated patch-clamp system, we compared the affinity of BeKm-1 for hERG channels with some reference compounds. We fully assessed its effects on the electrophysiological, calcium handling, and beating properties of hiPS-CMs. By delaying cardiomyocyte repolarization, the peptide induces early afterdepolarizations and reduces spontaneous action potentials, calcium transients, and contraction frequencies, therefore recapitulating several of the critical phenotype features associated with arrhythmic risk in drug-induced LQTS. BeKm-1 exemplifies an interesting reference compound in the integrated hiPS-CMs cell model for all drugs that may block the hERG channel from the outer face. Being a peptide that is easily modifiable, it will serve as an ideal molecular platform for the design of new hERG modulators displaying additional functionalities.