Fig. 5: A unique dual-PIP2 modulation mechanism of KCNQ1 + KCNE1.
From: Secondary structure transitions and dual PIP2 binding define cardiac KCNQ1-KCNE1 channel gating
a In (KCNQ1 + KCNE1)APO, an endogenous PIP2E molecule was observed in the canonical PIP2-binding site (involving residues R181, K183, K196, and R249), while the CaM is in the attached mode. b The extended S4 hinge in (KCNQ1 + KCNE1)APO shows smaller distance to the PIP2 molecule than that in KCNQ1PIP2 (from 4.6 Å to 6.9 Å, PDB: 7XNL30). c In (KCNQ1 + KCNE1)PIP2, two PIP2 molecules (PIP2-1 and PIP2-2) were observed in each KCNQ1 subunit: PIP2-1 in the canonical site, and PIP2-2 between S4–S5 linker, S6’, and KCNE1 (involving residues R259, K358, Q359, K362, and KCNE1-R67), while the CaM is in the detached mode. Density maps and models of PIP2-1 and PIP2-2 are shown in orange and dark green, respectively. d Structural comparison of KCNE1 between (KCNQ1 + KCNE1)APO (gray) and (KCNQ1 + KCNE1)PIP2 (red) to show that PIP2-2 binding induces ~3 Å movement of the bottom part of KCNE1 without altering the top part. e G–V relations of alanine mutagenesis scanning of PIP2-1 and PIP2-2 binding residues in the absence and presence of KCNE1: V50 = –22.4 ± 2.8 mV for R181A (n = 4); V50 = 36.1 ± 2.4 mV for R181A + KCNE1 (n = 5); V50 = –15.1 ± 1.5 mV for K183A (n = 4); V50 = 52.2 ± 3.5 mV for K183A + KCNE1 (n = 4); V50 = –20.8 ± 1.0 mV for K196A (n = 4); V50 = 63.8 ± 3.4 mV for K196A + KCNE1 (n = 4); V50 = –9.3 ± 1.6 mV for R249A (n = 5); V50 = 37.9 ± 2.7 mV for R249A + KCNE1 (n = 4); V50 = 2.4 ± 1.2 mV for R259A (n = 6); V50 = 86.0 ± 5.2 mV for R259A + KCNE1 (n = 5); V50 = –6.9 ± 0.9 mV for K358A (n = 4); V50 = 43.8 ± 3.2 mV for K358A + KCNE1 (n = 6); V50 = –19.6 ± 2.5 mV for Q359A (n = 4); V50 = 66.1 ± 4.8 mV for Q359A + KCNE1 (n = 5); V50 = –14.4 ± 0.9 mV for K362A (n = 4); V50 = 95.8 ± 9.4 mV for K362A + KCNE1 (n = 5). For R67 on KCNE1, KCNQ1 + R67A was tested (V50 = 76.0 ± 1.2 mV, n = 4). f Cartoon schemes showing KCNE1-induced global structural remodeling of KCNQ1, and the gating process of KCNQ1 + KCNE1. Briefly, KCNE1 stabilizes the VSD in the intermediate state (with a PIP2 binds to the canonical site), and induces six helix-to-loop transitions (red lines) per KCNQ1 subunit, keeping the KCNQ1 + KCNE1 channel in the IC state. Upon depolarization, the VSD transitions to the activated state, three loops from S6 undergo loop-to-helix transitions to form a continues helix along S6 and HA, and a second PIP2 binds to stabilize the KCNQ1 + KCNE1 channel in the AO state.
