The degree of helix inclination is adjusted to maintain the hydrophobic interaction between the TM domain and lipids. (A) Illustration of the protein–lipid hydrophobic interaction, which was evaluated by the surface area of the nonpolar atoms (shown in gray and transparent surface representation) in TM helices that fall within 5 Å of the carbon atoms in lipid tails. (B) Distributions of hydrophobic surface area for FcγRIIB-I232 and FcγRIIB-T232 TM helices at various tilting angles (8–20°, 20–32°, and 32–44°). (C) Decomposition of the hydrophobic surface area to the contribution of each residue for the FcγRIIB-I232 TM helix tilting by 8–20° (black) and the FcγRIIB-T232 TM helix tilting by 32–44° (red). Error bar represent the mean ± SD. (D) Probability distributions of positions of the side groups of Met222 (MET; black) and Lys249 (LYS; red) along the axis perpendicular to the membrane surface in the FcγRIIB-I232 (continuous lines) and FcγRIIB-T232 (dashed lines) systems, respectively. The borders of the membrane bilayers are indicated by the same distributions of phosphorus atoms (blue) in the phospholipid molecules located in the two leaflets. (A–D) All the MD results have been verified in three independent experiments, using different force fields and different lipid composition.