Beckman Fellow 1999-00

Paul R Selvin


Assistant professor of physics and biophysics

Professor Selvin is studying how nerves work at the molecular level. When a nerve fires, sodium and potassium ions rush through the nerve cell membrane, creating little electrical currents. These currents are the bits of information in the nervous system, enabling us to perceive the world, tell our muscles to contract, and do everything that nerves do. Ordinarily, ions cannot normally pass through the cell membrane, but there are specialized channels (proteins) in the membrane that act as switches, transiently opening to allow ions through, and then closing. These ion channels have been studied for more than four decades, yet much about how they go from the “off" to the “on” state, and visa-versa, is not known. He wishes to visualize what the switch looks like when “off" and when “on," and to watch them in transition. Because the channels are very small (a few tenths of a nanometer), direct visualization is not possible. Instead, he labels the proteins with fluorescent dyes--probes which emit light following excitation with shorter-wavelength light. (For example, shine blue light at the dye and it might emit green light back.) Its importance is that the emitted light can reveal information about the local environment directly around the dye--e.g., if the protein changes shape around the dye, the dye’s emitted light may change properties. In addition, he proposes to look at one ion channel at a time, rather than the usual method of looking at thousands or millions of ion channels simultaneously. The importance of single-molecule measurements is that they can provide information not only about the average property or shape of the molecules, but also about the distribution or range of shapes as well. In this way, he hopes to gain insight into the workings of this most-important biological switch.