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. 2024 Sep 2;12:RP90851. doi: 10.7554/eLife.90851

Figure 3. The 2:1 sphingomyelin/cholesterol bilayer surrounding aquaporin-0 (AQP0) is similar to bilayers formed by phosphoglycerolipids.

(A) The top panel shows the seven sphingomyelins (light green sticks) and one cholesterol (orange sticks) molecules forming the bilayer around an AQP0 subunit (gray surface). The bottom panel shows just the lipid bilayer. (B) The top panel shows dimyristoyl phosphatidylcholine (DMPC) lipids (purple sticks) surrounding an AQP0 subunit (Gonen et al., 2005) and the bottom layer shows an overlay of the DMPC bilayer with the 2:1 sphingomyelin/cholesterol bilayer. (C) The top panel shows an Escherichia coli polar lipids extract (EPL) bilayer (modeled as PE lipids) (light brown sticks) surrounding an AQP0 subunit (Hite et al., 2010) and the bottom layer shows an overlay of the EPL bilayer with the 2:1 sphingomyelin/cholesterol bilayer. See also Figure 3—figure supplements 1–3 and Table 3.

Figure 3.

Figure 3—figure supplement 1. Distribution of sphingomyelin and cholesterol molecules around aquaporin-0 (AQP0) in two-dimensional (2D) crystals.

Figure 3—figure supplement 1.

(A–B) 2D crystals grown with a molar sphingomyelin:cholesterol ratio of 2:1. (C–D) 2D crystals grown with a molar sphingomyelin:cholesterol ratio of 1:2. Lipid distribution in AQP0 arrays formed with a molar sphingomyelin:cholesterol ratio of 2:1. Panels (A) and (C) show the side view of a single AQP0 subunit, and panels (B) and (D) show a top view of four subunits (from different tetramers) in the area where four different tetramers come together in the array. Note that lipids at the crystallographic fourfold axis could not be modeled.
Figure 3—figure supplement 2. Structure comparisons of aquaporin-0 (AQP0) in different lipid bilayers.

Figure 3—figure supplement 2.

The root mean square deviation (RMSD) between the Cα atoms of AQP0 structures determined in membranes formed with different lipids is very low and variations between structures are largely constrained to extramembranous loops. (A) AQP02SM:1Chol (light green) versus AQP0DMPC (purple). (B) AQP02SM:1Chol (light green) versus AQP0EPL (blue). (C) AQP01SM:2Chol (dark green) versus AQP0DMPC (purple). (D) AQP01SM:2Chol (dark green) versus AQP0DMPC (purple). (E) AQP02SM:1Chol (light green) versus AQP01SM:2Chol (dark green).
Figure 3—figure supplement 3. Interactions of sphingomyelin lipids in AQP02SM:1Chol with aquaporin-0 (AQP0) and Chol1.

Figure 3—figure supplement 3.

(A) The head group of sphingomyelin SM3 interacts with AQP0 residues Tyr-105 and Arg-196. Yellow dashed lines indicate the hydrogen bonds. (B) The acyl chains of sphingomyelins SM1, SM2, SM5, and SM5’ have hydrophobic interactions with cholesterol Chol1, as well as AQP0 residues of His-201, Trp-205, Val-90, and Ile-87.