1.A.2.1.2
G-protein enhanced inward rectifier K channel 2, IRK1, IRK2, KCNJ2, KCNJ5, Kir2.1 (Andersen-Tawil Syndrome (ATS-1) protein; the V302M mutation causing the syndrome, alters the G-loop cytoplasmic K conduction pathway) (Bendahhou et al., 2003; Ma et al., 2007). (Blocked by chloroquine which binds in the cytoplasmic pore domain (Rodriguez-Menchaca et al., 2008)). Forms heteromultimers with Kir3.1 and Kir3.4 (Ishihara et al., 2009). A C-terminal domain is critical for the sensitivity of Kir2.1 to cholesterol (Epshtein et al., 2009). Flecainide increases Kir2.1 currents by interacting with cysteine 311, decreasing the polyamine-induced rectification (Caballero et al., 2010).  The inhibitory cholesterol binding site has been identified (Fürst et al. 2014).  Polyamines and Mg²⁺ block ion flux synergistically (Huang and Kuo 2016). Long polyamines serve a dual role as both blockers and coactivators (with PIP2) of Kir2.1 channels (Xie et al. 2005).  Cytoplasmic domain structures of Kir2.1 and Kir3.1 show sites for modulating gating and rectification (Pegan et al. 2005). Loss-of-function mutations are a rare cause of long QT syndrome (Fodstad et al. 2004). Fibroblast growth factor 21 ameliorates NaV1.5 and Kir2.1 channel dysregulation in human AC16 cardiomyocytes (Li et al. 2021). The trafficking of Kir2.1 and its role in development have been reviewed (Hager et al. 2021). Cholesterol-induced suppression of Kir2 channels is mediated by decoupling at the inter-subunit interfaces (Barbera et al. 2022). CryoEM studies have revealed a well-connected network of interactions between the PIP2-binding site and the G-loop through residues R312 and H221.Moreover, the intrinsic tendency of the CTD to tether to the TMD and a movement of the secondary anionic binding site to the membrane even without PIP2 was revealed (Fernandes et al. 2022). The results revealed structural features unique to human Kir2.1. Individual protonation events change the electrostatic microenvironment of the pore, resulting in distinct, uncoordinated, and relatively long-lasting conductance states, which depend on levels of ion pooling in the pore and the maintenance of pore wetting (Maksaev et al. 2023). Subunit gating results from individual protonation events in Kir2 channels (Maksaev et al. 2023).