Rod MacKinnon woke up on 1 January 1998 with a sickening feeling that his eureka moment had been a dream. Late into the night, at Cornell University's synchrotron light source in Ithaca, New York, he had been processing data on the structure of a crystallized potassium-ion channel from a cell membrane. Eventually, his colleagues left to join the New Year celebrations, and MacKinnon worked on alone. Midnight passed, and with each iteration of the data, the image of the channel on his computer screen became clearer. Then, in the channel, shadows of multiple potassium ions began to emerge, lined up like pinballs, exactly as had been predicted some 50 years earlier. "I became so shaky I couldn't hit the keys, and I had no one to tell," MacKinnon recalls. Eventually he went to bed, the excitement of his discovery still buzzing round his head. Fortunately for MacKinnon, this was no dream. It was, in fact, a stunning highlight among a series of revelations about ion channels to emerge from his lab. And it was all the more remarkable for the fact that, when MacKinnon embarked on his quest to unveil the channels' structures just a few years before, many structural biologists had regarded him as foolhardy. Didn't he realize that ion channels were almost impossible to crystallize for X-ray structural analysis? Ion channels are proteins embedded in cell membranes. They act as extremely selective gateways, allowing specific ions to pass in and out of the cell in response to various signals. Most dramatically, they mediate the electrical impulses known as action potentials that are the basis of communication in the nervous system.
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