OHSU

Dawson Lab

Most people are surprised to learn that two devastating childhood diseases, cystic fibrosis and secretory diarrhea, are closely linked. Cystic Fibrosis is the most common lethal genetic disease among Caucasians, affecting 1/2500 live births. Although the cystic fibrosis gene was identified nearly 20 years ago, a cure for the disease has remained elusive. Secretory diarrhea is an infectious disease that is the leading cause of infant death world-wide. A major world health problem, diarrheal disease causes billions of dollars of lost productivity in the U.S. alone.

Both of these diseases are caused by abnormal regulation of the same molecule, a protein called CFTR that is found in cells of the human lung, pancreas, liver, and GI tract. The protein functions as a gate which controls the movement of chloride ions out of cells. In cystic fibrosis, genetic mutations alter the protein such that the channel is defective and chloride movement is reduced or absent. Reduced chloride movement in the cells of the lung produces thick, sticky mucus which becomes a breeding ground for bacteria and can cause a fatal plugging of the airways. In secretory diarrhea, like that produced by cholera, bacterial toxins alter cells of the intestine so that the CFTR gate cannot close. The resulting excessive chloride ion loss from the cells causes life-threatening loss of salt and water or dehydration.

The goal of the research carried out in Dr. Dawson's lab is to provide the scientific basis for the development of drugs that can be used to treat these two lethal diseases of childhood. The research combines high-resolution electrophysiological measurements of CFTR behavior with chemical modification strategies designed to reveal what parts of the CFTR molecule are most important for its vital functions. This information is used to refine atomic scale models for the protein. Understanding how this complex molecule does its job will provide the foundation for the design of drugs or other therapies that can be used to increase the activity of CFTR in cystic fibrosis patients or to decrease the activity of CFTR in people suffering from secretory diarrhea.

Two-electrode voltage clamp is used to measure chloride currents in Xenopus oocytes expressing CFTR TEVC close-up


 

A panel of thiol-reactive chemicals is used to probe CFTRs where single amino acids have been selectively mutated to cysteine chemical probes short-list


 


One strategy for developing an atomic-scale model of CFTR is to use a crystal structure of a related protein as a template for creating a homology model.  Shown here is a structure of Sav1866, a bacterial multi-drug resistance ABC transporter.
SAV1866


 

First map of TM6:  Channel-impermeant reagents.  Results from chemical-modification experiments can be used to refine atomic-scale models. TM6 reactivity