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ICl2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is one-dimensional and consists of two ICl2 ribbons oriented in the (0, 0, 1) direction. I is bonded in a distorted rectangular see-saw-like geometry to four equivalent Cl atoms. All I–Cl bond lengths are 2.71 Å. Cl is bonded in a water-like geometry to two equivalent I atoms.
Cs2Pd(ICl2)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Cs1+ is bonded in a 8-coordinate geometry to four equivalent I1- and eight equivalent Cl1- atoms. All Cs–I bond lengths are 4.28 Å. All Cs–Cl bond lengths are 3.78 Å. Pd4+ is bonded in a distorted octahedral geometry to two equivalent I1- and four equivalent Cl1- atoms. Both Pd–I bond lengths are 3.10 Å. All Pd–Cl bond lengths are 2.33 Å. I1- is bonded in a 1-coordinate geometry to four equivalent Cs1+, one Pd4+, one I1-, and eight equivalent Cl1- atoms. The I–I bond length is 2.85 Å. There are four shorter (3.87 Å) and four longer (3.88 Å) I–Cl bond lengths. Cl1- is bonded in a distorted single-bond geometry to four equivalent Cs1+, one Pd4+, and four equivalent I1- atoms.
The human calcium-sensing receptor (CaSR) detects fluctuations in the extracellular Ca 2+ concentration and maintains Ca 2+ homeostasis. It also mediates diverse cellular processes not associated with Ca 2+ balance. The functional pleiotropy of CaSR arises in part from its ability to signal through several G-protein subtypes. Here, we determined structures of CaSR in complex with G proteins from three different subfamilies: G q , G i and G s . We found that the homodimeric CaSR of each complex couples to a single G protein through a common mode. This involves the C-terminal helix of each Gα subunit binding to a shallow pocket that is formed in one CaSR subunit by all three intracellular loops (ICL1–ICL3), an extended transmembrane helix 3 and an ordered C-terminal region. G-protein binding expands the transmembrane dimer interface, which is further stabilized by phospholipid. The restraint imposed by the receptor dimer, in combination with ICL2, enables G-protein activation by facilitating conformational transition of Gα. We identified a single Gα residue that determines G q and G s versus G i selectivity. The length and flexibility of ICL2 allows CaSR to bind all three Gα subtypes, thereby conferring capacity for promiscuous G-protein coupling.
PCl4ICl2 is beta-prime cadmium gold structured and crystallizes in the tetragonal P-42_1m space group. The structure is zero-dimensional and consists of two [pcl4]+1 molecules and two ICl2 clusters. In each ICl2 cluster, I is bonded in a linear geometry to two equivalent Cl atoms. Both I–Cl bond lengths are 2.58 Å. Cl is bonded in a single-bond geometry to one I atom.