March 10, 1998
Scientists take another step forward in CF research
TORONTO - Scientists at The Hospital for Sick Children (SickKids) and the University of Toronto (U of T) have provided the first structural evidence that the defective cystic fibrosis (CF) gene leads to a malformation of the protein that carries out the gene's biochemical orders. The discovery has important implications for developing new therapies for CF and other diseases caused by protein malformation. The research is reported in the March issue of Nature Structural Biology.
The cystic fibrosis gene produces a protein (called the Cystic Fibrosis Transmembrane Conductance Regulator, or CFTR) which is active in the pancreas, reproductive tracts, sweat glands, and the cells that line the lungs. The CFTR protein functions as a pore at the cell surface and allows, under certain conditions, the movement of salt and water across cell layers. When salt and water are not able to cross the cell surface, the result is dry, thick mucus. It is this mucus which causes breathing and digestion problems for people with CF. Patients whose lungs are affected often die before adulthood, and invariably before middle age.
As do all genes, the CF gene contains instructions to make a protein that carries out its specific function. In the first stage of the CFTR protein's development, it takes the form of a long string of 1,480 amino acids. In order to do its job, the protein must then "fold" itself into a complicated and compact three-dimensional structure. This folding process or maturation process occurs inside the cell and brings together sections of the protein that are often linearly distant. Once the protein reaches its mature shape, it triggers a further series of actions and is transported to the cell surface where it carries out its work as a pore.
"In the case of most people with CF, one of the amino acids in the protein is missing," explains Dr. Gergely Lukacs, SickKids cell biologist and assistant professor of Laboratory Medicine and Pathobiology, U of T. "This defect causes the CFTR protein to stop "folding" before it reaches a state of maturity. As a result, the protein is retained inside the cell and can not carry out its function as a regulated pore at the cell surface."
Previous attempts to study the CFTR protein structure, using traditional techniques such as x-ray crystallography and nuclear magnetic resonance, have yielded unsatisfactory results. In this current research, Dr. Lukacs and his colleagues Dr. Norbert Kartner, Assistant Professor of Pharmacology, U of T, and SickKids research assistant Fred Zhang, used biochemical and radioactive techniques that enabled them to visualize certain structural features of both immature and mature proteins in their native environment.
"This method has enabled us, for the first time, to obtain a bird's-eye view of the structural differences between the normal and defective forms of the CFTR protein," explains Dr Lukacs. "The next step will be to look at possible ways to help the protein to complete the folding process."
This research was supported by the Canadian Cystic Fibrosis Foundation, the Medical Research Council of Canada, and the National Institutes of Health.
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