Figure 6.

Determining the optimal membrane shape for a fixed charge in the core of the membrane. (A) Starting with the arginine at the center of the membrane as in Fig. 5 F, the helix was held fixed, and the point of contact of the upper membrane–water interface with the helix was varied from a height of 0 Å to its equilibrium width of 21 Å. The electrostatic energy decreases by 35 kcal/mol as the arginine residue gains access to the polar head groups and extracellular water. The majority of the decrease in electrostatic energy occurs from 21 to 5 Å, and there is pronounced flattening in the curve between 0 and 5 Å. (B) The total insertion energy exhibits a well-defined energy minimum at a contact membrane height of 5 Å.