A three-dimensional image of a protein called TRPV1 has been created by rresearchers at Baylor College of Medicine in Houston. This protein is thought to enable a person to sense the heat of a hot pepper
Describing their work in the Proceedings of the National Academy of Sciences, the researchers revealed that they used sophisticated equipment for the purpose.
The researchers believe that the new image may give them significant insights into how an outside stimulus affects the nerve cell.
"This protein, known as TRPV1, not only senses spicy foods, but also makes it possible to feel real heat and the pain and inflammation related to other medical conditions," said Dr. Theodore G. Wensel, a professor of Biochemistry and Molecular Biology at BCM.
"This method of viewing the protein now gives us the chance to clearly see the functional relationship between outside stimuli and the nerve cell," added the senior author of the study.
The researchers said that TRPV1 is found on the nerve cell membrane, and that the burning sensation results from the action of a chemical called capsaicin on this protein.
They described TRPV1 as an ion channel, a tiny pore on the cell membrane, which allows chemicals such as calcium to flux in and out.
"Any time you feel a burn or pain sensation, it is mediated by a TRPV1 channel. Different levels of heat are mediated by different TRP channels. They are all related but each is regulated in a different manner," said Dr. Vera Moiseenkova-Bell, a postdoctoral associate in Wensel's laboratory at BCM and first author of the study.
Dr. Wensel revealed the three-dimensional image of this protein has revealed a number of surprising facts about its structure.
He said that the protein is made up of a pore domain embedded in the cell membrane, and a "hanging basket" of regulatory domains that extend into the interior of the cell.
"It's an unusual thing. There is a whole hollow 'basket' area but we don't know what's that's for. Now the search is on to understand how the 'basket' area regulates the channel," Wensel said.
The researchers say that the thee-dimensional image of this protein has provided them with an idea as to the structure of other channels too.
"Visualization of TRPV1 gives us insight on other TRP channels since they are structurally similar. Pharmaceutical companies target these TRP channels to make sure the drug binds properly. With this first structure we can start to build models of binding sites and hopefully in the future design more effective pharmaceuticals for a wide range of medical conditions," said Moiseenkova-Bell.
Scientists were earlier unclear what each TRP channel was responding to, and determining which proteins interacted with TRPV1 needed Wensel's lab to create a purified model.
The protein had to be removed from cells, purified, and reconstituted in a synthetic membrane so that the researchers could control channel activity.
"Since calcium is involved in cell signalling, following the calcium movement confirmed the protein is active. We are the first group to purify a TRPV1 channel and control what goes in and out when the channel opens," said Wensel.