Resolving the 3D structure of IC1N, a candidate for the swelling dependent anion channel

The elucidation of the structure of proteins and protein complexes will have a tremendous impact in physiology and hence in modern medicine. It will help to understand how a protein operates and allow the design of specific drugs, leading to the understanding of a protein`s role in physiological or pathophysiological processes. As deviations in the chloride permeability of cells are the basis of various human inherited diseases such as mukoviscidosis or myotonia congenita, chloride channels are currently in the focus of extensive research. Since there is evidence that swelling-dependent chloride channels are activated during pathological processes like the onset of exercised induced asthma or arrhythmia in the heart, we set out to determine the structure of ICln, a candidate for the swelling dependent chloride channel. The aims of the proposed project are to resolve the three- dimensional (3D) structure of ICln within the membrane using electron cryomicroscopy on two-dimensional (2D) crystals and to establish structure analysis of membrane proteins using electron microscopy in Innsbruck. Since membrane proteins proofed to be very difficult to crystallise in three dimensions in a lipidic phase or in detergent micelles for X-ray crystallography, electron cryomicroscopy is the method of choice to study the structure of channel proteins. A further advantage of 2D electron cryomicroscopy is that the protein under study can be observed in its natural environment, the membrane. The results of this study can help to shed light upon physiological and biophysical characteristics of ICln namely the oligomeric state, the potential location of binding sites for blockers or the selectivity gate, as well as the basis of rectification. Since up to now no specific drugs for a single class of anion channels are available, a fact which limits both the studying of the physiological role of ICln and the therapeutical intervention in pathological processes, knowledge of the 3D structure of ICln would be of invaluable help for drug design. Once the technical know-how has been acquired in a leading laboratory, structure analysis of membrane proteins using electron microscopy could be established in Innsbruck with the equipment available. This is especially important, since structure analysis of membrane proteins using electron cryomicroscopy is a rapidly developing discipline, likely to revolutionize our understanding of how ion channels and transporters work.