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Fig. 3 | BMC Biology

Fig. 3

From: Ion- and water-binding sites inside an occluded hourglass pore of a trimeric intracellular cation (TRIC) channel

Fig. 3

Ion- and water-binding sites within the pores of SsTRIC channel. a Structure of a SsTRIC homotrimer at 2.2-Å resolution viewed along the membrane plane. The estimated position of membrane is indicated by the light gray boxes. The K+ ions and water molecules within the pore region are shown as purple and red spheres, respectively. b The SsTRIC trimer viewed along the C3 axis from the cytoplasmic side. The green meshes indicate the 2F o-F c electron density (contoured at +1.0 × σ level) of a neutral lipid molecule. c The pore running through SsTRIC monomer is indicated by the tri-color dotted areas. Red areas, radius <1.15 Å; green areas, 1.15 Å < radius < 2.30 Å; blue areas, radius >2.30 Å. G1–G4 label the pore constriction sites (or gates) as shown by the red areas, while the green areas contain the binding sites for ion or water molecules labeled as P1′, P0′, P0, P1–P3 in d. The key amino acid residues lining the pore lumen are shown as stick models. From middle to bottom, they are F104, F16, Y153, R137, D138, and M146. d Distribution of K+ ions or water molecules within the pore region of an SsTRIC monomer. The sectional view of a monomer is shown as the electrostatic potential surface model overlaid with the cartoon model (color code: deep red, electronegative; deep blue, electropositive; silver, cartoon model of the protein backbone). The distances between two adjacent molecules are shown by the numbers (Å) labeled around the dashed lines. e A zoom-in view of the pore center with two ion-/water-binding sites. K+ ions and water molecules are shown as silver and red bullets, respectively. Oxygen, nitrogen, and carbon atoms of the amino acid residues are colored red, blue, and yellow, respectively. The interactions between K+ ion on P0′ site (or water molecule on P0 site) and the surrounding residues are indicated by the dashed lines with their distances (Å) labeled nearby. f The pore center viewed from a different angle to show the water molecule on P0 site and its surrounding residues

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