A heme-binding domain controls regulation of ATP-dependent potassium channels

Significance Heme-containing proteins are found in all living species and carry out a wide variety of biological functions. It is becoming clear that heme has a wider regulatory role in the cell; one such regulatory role is in control of ion channel function. In this paper, we demonstrated heme-dependent regulation of KATP channels and identified the heme-binding location as being on a sulphonylurea receptor subunit of the channel. We use this information to present a hypothesis for how heme regulation across numerous ion channels may occur. Heme iron has many and varied roles in biology. Most commonly it binds as a prosthetic group to proteins, and it has been widely supposed and amply demonstrated that subtle variations in the protein structure around the heme, including the heme ligands, are used to control the reactivity of the metal ion. However, the role of heme in biology now appears to also include a regulatory responsibility in the cell; this includes regulation of ion channel function. In this work, we show that cardiac KATP channels are regulated by heme. We identify a cytoplasmic heme-binding CXXHX16H motif on the sulphonylurea receptor subunit of the channel, and mutagenesis together with quantitative and spectroscopic analyses of heme-binding and single channel experiments identified Cys628 and His648 as important for heme binding. We discuss the wider implications of these findings and we use the information to present hypotheses for mechanisms of heme-dependent regulation across other ion channels.