Development of ASIC1a ligand-gated ion channel drug screening assays across multiple automated patch clamp platforms

The funnel-web spider venom derived single knot peptide Hc3a modulates acid-sensing ion channel 1a desensitisation

Acid-sensing ion channel 1a (ASIC1a) is a proton-gated channel involved in synaptic transmission, pain signalling, and several ischemia-associated pathological conditions. The spider venom-derived peptides PcTx1 and Hi1a are two of the most potent ASIC1a inhibitors known and have been instrumental in furthering our understanding of the structure, function, and biological roles of ASICs. To date, homologous spider peptides with different pharmacological profiles at ASIC1a have yet to be discovered. Here we report the characterisation of Hc3a, a single inhibitor cystine knot peptide from the Australian funnel-web spider Hadronyche cerberea with sequence similarity to PcTx1. We show that Hc3a has complex pharmacology and binds different ASIC1a conformational states (closed, open, and desensitised) with different affinities, with the most prominent effect on desensitisation. Hc3a slows the desensitisation kinetics of proton-activated ASIC1a currents across multiple application pHs, and when bound directly to ASIC1a in the desensitised conformation promotes current inhibition. The solution structure of Hc3a was solved, and the peptide-channel interaction examined via mutagenesis studies to highlight how small differences in sequence between Hc3a and PcTx1 can lead to peptides with distinct pharmacology. The discovery of Hc3a expands the pharmacological diversity of spider venom peptides targeting ASIC1a and adds to the toolbox of compounds to study the intricacies of ASIC1 gating.

Revealing molecular determinants governing mambalgin-3 pharmacology at acid-sensing ion channel 1 variants

Acid-sensing ion channels (ASICs) are trimeric proton-gated cation channels that play a role in neurotransmission and pain sensation. The snake venom-derived peptides, mambalgins, exhibit potent analgesic effects in rodents by inhibiting central ASIC1a and peripheral ASIC1b. Despite their distinct species- and subtype-dependent pharmacology, previous structure-function studies have focussed on the mambalgin interaction with ASIC1a. Currently, the specific channel residues responsible for this pharmacological profile, and the mambalgin pharmacophore at ASIC1b remain unknown. Here we identify non-conserved residues at the ASIC1 subunit interface that drive differences in the mambalgin pharmacology from rat ASIC1a to ASIC1b, some of which likely do not make peptide binding interactions. Additionally, an amino acid variation below the core binding site explains potency differences between rat and human ASIC1. Two regions within the palm domain, which contribute to subtype-dependent effects for mambalgins, play key roles in ASIC gating, consistent with subtype-specific differences in the peptides mechanism. Lastly, there is a shared primary mambalgin pharmacophore for ASIC1a and ASIC1b activity, with certain peripheral peptide residues showing variant-specific significance for potency. Through our broad mutagenesis studies across various species and subtype variants, we gain a more comprehensive understanding of the pharmacophore and the intricate molecular interactions that underlie ligand specificity. These insights pave the way for the development of more potent and targeted peptide analogues required to advance our understating of human ASIC1 function and its role in disease.

Using automated patch clamp electrophysiology platforms in ion channel drug discovery: an industry perspective

INTRODUCTION

Automated patch clamp (APC) is now well established as a mature technology for ion channel drug discovery in academia, biotech and pharma companies, and in contract research organizations (CRO), for a variety of applications including channelopathy research, compound screening, target validation and cardiac safety testing.

AREAS COVERED

Ion channels are an important class of drugged and approved drug targets. The authors present a review of the current state of ion channel drug discovery along with new and exciting developments in ion channel research involving APC. This includes topics such as native and iPSC-derived cells in ion channel drug discovery, channelopathy research, organellar and biologics in ion channel drug discovery.

EXPERT OPINION

It is our belief that APC will continue to play a critical role in ion channel drug discovery, not only in 'classical' hit screening, target validation and cardiac safety testing, but extending these applications to include high throughput organellar recordings and optogenetics. In this way, with advancements in APC capabilities and applications, together with high resolution cryo-EM structures, ion channel drug discovery will be re-invigorated, leading to a growing list of ion channel ligands in clinical development.