Mechanism of Chloride Conduction in the CFTR Anion Channel

Each cell in our body is surrounded by a thin membrane that forms a barrier that separates the cell's contents from its environment. To cross this barrier, small substances have to use protein molecules that are present in the membrane. One example is a protein called CFTR, which controls salt and water movement in and out of cells. When this protein does not work properly, this results in the fatal disease cystic fibrosis. Research in my lab uses precise electrical recording techniques to study the movement of chloride ions, one component of salt, as they move through CFTR and across the cell membrane. These electrical recordings are so precise that we are able to detect and study chloride transport by a single CFTR protein molecule undergoing its normal activity in the cell membrane. We hope to understand how CFTR moves chloride ions extremely rapidly while at the same time not allowing other, similar small ions to pass through, a process known as selectivity between different ions. We believe that there must be specific parts of the CFTR protein that are able to recognize chloride ions and in this way select them for transport across the membrane. To understand how the CFTR protein molecule works, we change its structure by introducing designed changes into its gene using techniques of laboratory molecular biology. Normal and designer altered forms of CFTR are then introduced into cells growing in culture in the lab. This allows us to figure out, in fine detail, how the structure of CFTR determines its ability to transport chloride, using electrical recordings. We are particularly interested in understanding how the CFTR protein recognizes chloride ions, and once they have been selected, how they are transported across the membrane so quickly. We believe that more than one part of the pathway that chloride ions must move along to cross the membrane acts as a chloride recognition site, and that chloride ions present at different places within this pathway must somehow be able to sense one another's presence in order to continue their journey through CFTR and across the membrane. The proposed research is aimed at understanding these processes of chloride recognition and rapid chloride transport, central aspects to the normal job of this important protein. Other chloride transporting proteins also exist, and we expect much of what we learn about CFTR to also help understand how these other transport proteins work.