Fig. 8.

Transition toward the closed form of the CFTR channel: comparison of the MSDs from the different conformers along the MD2 simulation. A Global lateral view. Conformers 1 (0 and 5 ns), conformers i (10 and 15 ns) and conformers 2 (20 and 30 ns). B Focus (lateral view) on the membrane portions of TM1–TM2 (blue), TM5–TM6 (green), TM7–TM8 (yellow), and TM11–TM12 (red). Dark colors are associated with conformers 1 (0 and 5 ns), whereas conformers i (10 and 15 ns) and conformers 2 (20 and 30 ns) are represented with light colors. C Extracellular view of the superimposition of conformer 1 (0 ns, dark colors) with conformer i (10 ns, light colors). TM1–TM2 and TM11–TM12 couples of helices move about 5/6 Å toward TM6 and TM7, while TM5–TM6 and TM7–TM8 are only slightly displaced. The channel, whose pore is shown, is still open. Of note is the onset during MD2 of a small β-sheet between successive hydrophobic amino acids (within the sequence) belonging to ECL3 (G330, I331, and I332) and ECL4 (A904, V905, and I906), which may reinforce the interaction between the four TM5–TM6 and TM7–TM8 helices. D A similar extracellular view of the superimposition of conformer 1 (0 ns, dark colors) with conformer 2 (30 ns, light colors). TM1–TM2 and TM11–TM12 couples of helices have nearly completed their movements toward TM6 and TM7, whereas TM5–TM6 and TM7–TM8 moved toward the center for about 3.7 Å, leading to the complete closure of the channel. The side chains of F337, I106, and L1133, taken as examples, are in close contact