A sodium-mediated structural switch that controls the sensitivity of Kir channels to PtdIns(4,5)P2

Abstract

Inwardly rectifying potassium (Kir) channels are gated by the membrane phospholipid phosphatidylinositol-4,5-bisphosphate (PIP2). Among them, Kir3 channel gating requires additional molecules, such as the βγ subunits of G proteins or intracellular sodium. Using an interactive computational-experimental approach, we show that sodium sensitivity of Kir channels involves the side-chains of an aspartate and a histidine located across from each other in a critical loop in the cytosolic domain, as well as the backbone carbonyls of two additional residues and a water molecule. The location of the coordination site in the vicinity of a conserved arginine shown to affect channel-PIP2 interactions suggests that sodium triggers a structural switch that frees the critical arginine. Mutations of the aspartate and the histidine that affect sodium sensitivity also enhance the channel’s sensitivity to PIP2. Furthermore, based on the molecular characteristics of the coordination site, we identify and confirm experimentally a novel sodium-sensitive phenotype in Kir5.1.

A Critical Gating Switch at a Modulatory Site in Neuronal Kir3 Channels

“…‫ء‬ interacting with G␤␥ (Mahajan et al, 2013). The mutants constructed for the salt-bridge residue exchange experiment (Kir3.2 ‫ء‬ _S196R, Kir3.2 ‫ء‬ _R201E, and Kir3.2 ‫ء‬ _S196R_R201E) did not yield measurable current, which neither lent support nor refuted the salt-bridge hypothesis between phosphoSer-196 and Arg-201.…”

“…Homotetramers of Kir3.2 may exist in the substantia nigra pars compacta, where there does not appear to be expression of its usual heteromeric partner, Kir3.1 (Inanobe et al, 1999). Kir3.2 is readily activated by G␤␥ via Gi-coupled GPCRs (Logothetis et al, 1987;Hibino et al, 2010), whereas alternate pathways of control, such as channel inhibition via Gq-coupled GPCRs, are less well understood (Kobrinsky et al, 2000;Leaney et al, 2001;Brown et al, 2005;Hibino et al, 2010).…”

“…The net downstream effect of PKC activation on Kir3 channels is current inhibition, allowing for increased cellular excitability (Stevens et al, 1999;Mao et al, 2004;Keselman et al, 2007). Gq-coupled receptor activation also simultaneously depletes the local concentration of PIP 2 by hydrolysis to IP 3 , which decreases Kir3 channel activity because PIP 2 is a required component for activation of Kir3 channels (Huang et al, 1998;Zhang et al, 1999).…”

The KtrA and KtrE Subunits Are Required for Na + -Dependent K + Uptake by KtrB across the Plasma Membrane in Synechocystis sp. Strain PCC 6803

“…In Kir-type K ϩ channels, the negative residues in the cytosolic region have been identified as playing a crucial role in Na ϩ -dependent activation (10,37). Results obtained by an interactive computational-experimental approach based on the crystal structure of the cytosolic domain of Kir3.1 suggest that the Na ϩ binding motif in Kir-type channels is DXRXXH (26). However, this sequence is not present in KtrB.…”

Cholesterol sensitivity of KIR2.1 depends on functional inter-links between the N and C termini

“…19 Interestingly, the same CD loop residues also play a critical role in regulating the function of different Kir channels by other modulators including the phosphoinositide PI(4,5)P 2 , [23][24][25] which is required for Kir channel activation, 8,23,[26][27][28] and intracellular sodium. [29][30][31][32] We have previously shown that in addition to Kir2.1, also other members of the Kir2 subfamily were also suppressed by cholesterol. 9 However, whereas the sensitivity of Kir2.1 and Kir2.2 to cholesterol was similar, Kir2.3 and Kir2.4 exhibited residues to the corresponding residues in Kir2.2.…”