Heme is a carbon monoxide receptor for large-conductance Ca2+-activated K+ channels.
Carbon monoxide (CO) is an endogenous paracrine and autocrine gaseous messenger that regulates physiological functions in a wide variety of tissues. CO induces vasodilation by activating arterial smooth muscle large-conductance Ca2+-activated potassium (BK(Ca)) channels. However, the mechanism by which CO activates BK(Ca) channels remains unclear. Here, we tested the hypothesis that CO activates BK(Ca) channels by binding to channel-bound heme, a BK(Ca) channel inhibitor, and altering the interaction between heme and the conserved heme-binding domain (HBD) of the channel alpha subunit C terminus. Data obtained using thin-layer chromatography, spectrophotometry, mass spectrometry (MS), and MS-MS indicate that CO modifies the binding of reduced heme to the alpha subunit HBD. In contrast, CO does not alter the interaction between the HBD and oxidized heme (hemin), to which CO cannot bind. Consistent with these findings, electrophysiological measurements of native and cloned (cbv) cerebral artery smooth muscle BK(Ca) channels show that CO reverses BK(Ca) channel inhibition by heme but not by hemin. Site-directed mutagenesis of the cbv HBD from CKACH to CKASR abolished both heme-induced channel inhibition and CO-induced activation. Furthermore, on binding CO, heme switches from being a channel inhibitor to an activator. These findings indicate that reduced heme is a functional CO receptor for BK(Ca) channels, introduce a unique mechanism by which CO regulates the activity of a target protein, and reveal a novel process by which a gaseous messenger regulates ion channel activity.
Jaggar
Jonathan H
JH
Department of Physiology, University of Tennessee Health Science Center, Memphis 38139, USA. jjaggar@physio1.utmem.edu
Li
Anlong
A
Parfenova
Helena
H
Liu
Jianxi
J
Umstot
Edward S
ES
Dopico
Alejandro M
AM
Leffler
Charles W
CW
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002248:Carbon Monoxide / Q000378:metabolism / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism; D002522:Chlorocebus aethiops; D006418:Heme / Q000378:metabolism* / Q000494:pharmacology; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000378:metabolism; D006427:Hemin / Q000494:pharmacology; D008969:Molecular Sequence Data; D010100:Oxygen / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D051381:Rats
D002352:Carrier Proteins; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D024681:Potassium Channels, Calcium-Activated; D006418:Heme; D006427:Hemin; D002248:Carbon Monoxide; D010100:Oxygen