Study of vision disorder leads to discovery of new family of io...( electrooculograms tests that measures...)

electrooculograms, tests that measures ion movements in the eye. In addition, all people who inherit one copy of the mutated bestrophin gene and one normal copy of the gene have the disease. This fact led the scientists to believe that when the defective protein is present, it actively prevents the normal protein from functioning properly.

To study the protein, the scientists produced the human bestrophin protein and studied its ability to conduct chloride ions across a cell membrane. Yau and HHMI associate Takashi Tsunenari performed detailed studies of the electrical conductance of the bestrophin protein after it was expressed in an embryonic kidney cell.

When an ion channel opens, a large flux of ions occurs, said Yau. Its like a floodgate opening. With amplification, it is possible from even one cell to pick up the current. And from the behavior of the current we can derive a signature of each channel.

This information provided evidence that the protein was indeed a chloride ion channel. But Nathans points out that many scientists had been fooled in the past into thinking they had found an ion channel when what they were actually seeing was the activity of their test cell, not the protein they were studying.

To prove they had found an ion channel, the scientists conducted several additional studies in which they tested bestrophin family members from the fruit fly and the worm. Each produced its own distinct ion channel signature, said Yau. In addition, when they tested the mutant bestrophin protein together with a normal bestrophin protein, they found that the mutant inhibited the electrical current produced by the normal protein.

Additional studies showed that the bestrophin protein assembles in a group of four or five units that form a pore through which the chloride ions pass. When mutant proteins assemble together with normal proteins, the result is a less effective channel. This explains why people with one copy
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
16-Apr-2002

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