Point by Point
To gain insight into how these ion channels achieve their temperature sensitivity, in the new study the scientists conducted studies of TRPV1, which was not only the first TRP to be discovered but is also the best understood. A previous study in the lab had focused on a related, warm-activated ion channel, TPRV3, but since the biophysics of this molecule is complicated, the team was unable to tease apart its mechanisms.
Using mutagenesis techniques, for the new study the scientists first generated some 8,500 mutants of TRPV1. Then, working with the high throughput equipment available at GNF, the team performed an unbiased screen of these compounds to identify mutations of interest.
"We were looking for mutations in these proteins that would only change the temperature sensitivity of these channels, but would not affect any of the other activation mechanisms," said Grandl. "We were looking for single-point mutations [changes of a single amino acid] where the channel still functioned normally in response to capsacin (the active ingredient in chili peppers) or pH, but not to temperature."
Indeed, the team found a number of these mutations that affected the molecule's sensitivity to temperature, but not to other cues. Interestingly, the mutations were clustered in one area of the protein, the outer pore region, which provides further support to the existence of the predicted 'temperature-sensor domain'.
Next, with these mutant versions of TRPV1 in hand, the scientists examined what had changed in the molecule to disrupt temperature sensitivity.
In findings new to the field, the team discovered that TRPV1 has two ways of opening its channelfor a brief time, opening for only for a millisecond before returning to its closed resting state, and for a relatively long time, opening for about 10 milliseconds. The team foun
|Contact: Keith McKeown|
Scripps Research Institute