![Figure 4. X-ray crystal structure of GLIC E−2′I + I9′A at pH 4.5. (A–D) Structural alignment of the models of GLIC E−2′I + I9′A at pH 4.5 (magenta) and GLIC WT at pH 4.0 (PDB ID code 4HFI; cyan). (E and F) M2 α-helices of two nonadjacent subunits of the double mutant. The approximate locations of the mutated side chains are indicated. Mesh representations show the 2Fo − Fc electron-density maps contoured at a level of 1.0σ. The narrowest constriction of this mutant’s pore occurs at the level of the engineered isoleucine side chains; its diameter (estimated using HOLE [Smart et al., 1996], and thus taking into account the atoms’ van der Waals radii) is ∼2.0 Å. (G) Cα profiles of the two structural models compared in (A–D). The five subunits of each model were averaged. Error bars (omitted if smaller than the symbols) are standard errors. Solid lines are cubic-spline interpolations. The lumen of the pore is to the right of the plot.](https://cdn.rupress.org/rup/content_public/journal/jgp/149/12/10.1085_jgp.201711803/5/jgp_201711803_fig4.jpeg?Expires=1767756881&Signature=ngZwD2~e0eZXneOaVekR1YJTrnjx7~ZlYruSFdXraQj6hi4mNT-NlkBRYVAA2Aj2UrH4vT8hb0a2U5JiRxUkv2JGUrKA1MaqurUMUkVEfsEQs-M~p-CfYHiGBHJDUoWIUe6A8m2v5htkiD~NJ31rmUDghzlYha3a2w4CsHJMCpFTBe0J4tLiTokP1rpBB8m5dMmRkUQWZS56xfS0nr7oAW6WG6P9lRahE6ymmfGH4bWXRep0YK~CPqKluSI3E91EwyMfQeDTkZaiba8AI1ZqgalpfYdYNKvMeFLNnV9nE3sUjQuOeRuOPvyeOhtKcebh416pkiBZpVv-ZE2y6uRyGQ__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
X-ray crystal structure of GLIC E−2′I + I9′A at pH 4.5. (A–D) Structural alignment of the models of GLIC E−2′I + I9′A at pH 4.5 (magenta) and GLIC WT at pH 4.0 (PDB ID code 4HFI; cyan). (E and F) M2 α-helices of two nonadjacent subunits of the double mutant. The approximate locations of the mutated side chains are indicated. Mesh representations show the 2Fo − Fc electron-density maps contoured at a level of 1.0σ. The narrowest constriction of this mutant’s pore occurs at the level of the engineered isoleucine side chains; its diameter (estimated using HOLE [Smart et al., 1996], and thus taking into account the atoms’ van der Waals radii) is ∼2.0 Å. (G) Cα profiles of the two structural models compared in (A–D). The five subunits of each model were averaged. Error bars (omitted if smaller than the symbols) are standard errors. Solid lines are cubic-spline interpolations. The lumen of the pore is to the right of the plot.
