Org34167 is an inhibitor of hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels, which are membrane proteins that exhibit tissue-specific expression profiles. HCN1, in particular, is primarily found in the brain, where it plays a critical role in neural signaling. This suggests that small molecule drugs with high specificity toward HCN1 are promising therapeutic candidates for treating epileptic seizures. Previous work has demonstrated that Org34167 alleviates epilepsy symptoms in a mouse model with an HCN1-related epilepsy mutation. Org34167 was shown to alter voltage-dependent gating of HCN1 channels and rescue cation leak that underlies HCN1 dysfunction in some developmental and epileptic encephalopathies. However, the site of interaction between the drug and protein is still unknown. Therefore, to investigate the binding interactions between Org34167 and HCN1, as well as the molecular determinants governing drug specificity, we sought to obtain a structure of the drug-protein complex. Here, we used single particle cryo-electron microscopy and electrophysiological assays to show that Org34167 binds to HCN1 within its transmembrane helices. We propose a model for the allosteric inhibition of HCN1 by Org34167 and how it is able to rescue cation leak resulting from HCN1 mutations. This work takes a critical step toward developing targeted therapies for epilepsy.
Kim et al. (Sun,) studied this question.