Fig. 5.

The R352–D993 salt bridge. A longitudinal cross-section of the molecular surface of the CFTR conformer 1, perpendicularly to the channel axis highlights crossing bridges within the pore, leading to observe a narrowed “hexagonal” pore channel (involving TM12/11/2/1/3/6), as well as a smaller pentagonal duct (involving TM6/5/8/7/9). The two pores of the CFTR channel are filled, for illustration, with chloride ions (in green). Ten TM helices surround the channels, while TM6 is more largely participating in both pores than TM12. The two remaining helices (TM4 and TM10) line the secondary lateral tunnel (see Fig. 2)