In 1989 he was appointed assistant professor at Harvard University where he studied the interaction of the potassium channel with a specific toxin taken from scorpion venom. He learned how to purify proteins and to use X-ray crystallography. In 1996, he moved to Rockefeller University as a professor and head of the Laboratory of Molecular Neurobiology and Biophysics. There, he started to work on the structure of the potassium channel. These channels are of particular importance to the nervous system and the heart. The channels enable potassium ions to cross the cell membrane.