Biochemical Studies of TRP Channel Activation and Modulation

Abstract

TRP channels are the cellular sensors behind many elements of somatosensation, including temperature sensing and the perception of pain. In fact, two channels, TRPV1 and TRPA1, expressed in pain-sensing nociceptor neurons, are direct molecular receptors for a number of painful thermal and chemical stimuli. Activation of those channels triggers action potentials in nociceptor neurons that signal pain to the central nervous system. Given the roles of TRPA1 and TRPV1 at the forefront of nociception, they are promising targets for reducing pain and inflammation through pharmacological intervention. Advancing our knowledge of the molecular mechanisms behind TRPV1 and TRPA1 channel activation and function is essential for the rational design of medically- and agriculturally-relevant channel modulators. With the entrance of TRP channels into the structural era, we are in the unique position to use structural information to direct, inform, and complement biochemical experiments. Together this knowledge helps us probe the molecular mechanical workings of TRP channels during activation. Here I present efforts to understand two modes of TRP channel activation: the vanilloid molecule-based activation of TRPV1 and the modulation of TRPA1 temperature sensitivity. Through mutagenesis and fluorescence-based characterization of TRPV1 channel function in insect cells, we identified a minimal set of residues responsible for species-specific differences in vanilloid sensitivity and engineered this sensitivity into a normally insensitive TRPV1 homolog. By systematic truncation and electrophysiological analysis of a highly temperature sensitive isoform of TRPA1, we identified a helix necessary for promoting temperature sensitivity and propose a structural role for the newly-recognized element. These insights on TRPV1 and TRPA1 function provide some of the missing molecular details of TRP channel activation by vanilloid compounds and temperature.