Discovery of a heme-binding domain in a neuronal voltage-gated potassium channel

The ether-a-go-go (EAG) family of voltage gated K+ channels are important regulators of neuronal and cardiac action potential firing (excitability) and have major roles in human diseases such as epilepsy, schizophrenia, cancer and sudden cardiac death. A defining feature of EAG (Kv10-12) channels  is a highly conserved domain on the amino-terminus, known as the eag-domain, consisting of a PAS domain capped by a short sequence containing an amphipathic helix (Cap-domain). The PAS and Cap domains are both vital for the normal function of EAG channels.  Using heme-affinity pull-down assays and proteomics of lysates from primary cortical neurons, we identified that an EAG channel, hERG3 (Kv11.3), binds to heme. In whole cell electrophysiology experiments, we identified that heme inhibits hERG3 channel activity. In addition, we expressed the Cap and PAS domain of hERG3 in E.coli and, using spectroscopy and kinetics, identified the PAS domain as the location for heme binding. The results identify heme as a regulator of hERG3 channel activity. These observations are discussed in the context of the emerging role for heme as a regulator of ion channel activity in cells.