Biochem Blogs

Biochemistry blog, science writing

Interaction between the Linker, Pre-S1, and TRP Domains Determines Folding, Assembly, and Trafficking of TRPV Channels

Graduate student Dmitry Grinevich

Primary Source: Valverde et al. “Interaction between the Linker, Pre-S1, and TRP Domains Determines Folding, Assembly, and Trafficking of TRPV Channels.” Cell Structure. August 4, 2015.

The thermo-TRP (transient receptor potential) ion channel family is an extremely interesting group of proteins to me because of their involvement in temperature sensing in a variety of different organisms. I think this is an exciting area to study because temperature is such a crucial part of every aspect of life, all the way down to the smallest molecular mechanisms. Temperature is clearly extremely important to understand because it controls every single chemical reaction that organisms depend on to function properly. The reason these TRP channels are so exciting is because they are the mechanism which many mammals use in sensing a range of temperatures. These channels are a family categorized by a few recurring features: N-terminal Ankyrin repeats, six transmembrane helices with a pore loop, and a C-terminal TRP domain.  Additionally, they are all membrane channels which open and close to allow the flow of calcium ions into cells which then leads to downstream responses to specific temperatures. There exist a variety of slightly different TRP channels which together are able to cover the full range of temperatures an organism needs to deal with, going as low as -20 degrees Celsius all the way up to over 50 degrees Celsius. Additionally, many of these channels are able to be activated by agonists which interact with them. For example, TRPV1, which is a heat sensing channel, can also be activated by both capsaicin (a vanilloid from hot peppers) and ethanol, both of which are chemicals that we can familiarly associate from food or drink with a feeling of heat. Because these channels are the molecular mechanism that our bodies use in order to sense temperature, I think it is exceedingly important for us to understand their structure and function in our cells. There is a great interest in these channels as a target for pain therapies and developing new analgesics. Some of the heat channels are known to be involved with pain responses which makes them potential candidates for targets for new pain relieving substances.

Valverde et al. explored a conserved amino acid motif common to all TRPV channels with the belief that it had a critical function. Site directed mutagenesis to disrupt this motif revealed that it is crucial to the cellular localization of TRPV4. On top of not properly localizing to membranes, the mutant TRPV4 channels also were unresponsive to activators, including heat, capsaicin, and exposure to a hypotonic solution. They were also able to replicate the same effects when this mutation is carried out in other TRPV channels. Next, they used confocal microscopy in order to study the subcellular localization of the mutant channels. What they found is that TRPV4 wild type colocalizes with cell membrane marker concanavalin-A, while the TRPV4 mutant colocalizes with the endoplasmic reticulum (ER) marker calreticulin. Next, they pinpointed more specific amino acid locations in various parts of the TRP channel domains to figure out which domain interactions are crucial for proper channel assembly. They were able to confirm through various site directed mutants that D425, E745, and K462 are all important resideus for interactions which lead to correct channel trafficking to the membrane. In the absence of any of these residues, channels are most likely not able to tetramerize properly and then cannot be exported from the ER to the plasma membrane to carry out normal functions. Finally, some molecular modeling allowed the authors to support their findings about the importance of these three residues.