| Popis: |
PIRT or Phosphoinositide regulator of TRP is a small membrane protein that has been shown to modulate the function of TRP channels. PIRT is implicated in fine-tuning the physiological roles that TRP channels play in thermosensing and ligand activation; suggesting roles for PIRT:TRP complexes in pathophysiologies such as pruritus and chronic pain. In an effort to better understand the mechanism of PIRT modulation of TRP channels, human PIRT has been expressed and purified. Solution NMR studies of the resulting protein have given way to backbone resonance assignment allowing for experimental determination of its secondary structure and membrane topology. PIRT contains a relatively unstructured N-terminus with two transmembrane helices followed by a positively charged PI(4,5)P2 interacting site in the juxtamembrane region near the C-terminus. Further residue specific characterization of PIRT interactions detail the residue specific binding of the phospholipid, phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), and the TRPM8 S1-S4 sensing domain. Interestingly, PIRT residues that specifically bind PI(4,5)P2 also specifically interact with the TRPM8 sensing domain. The overlap in PIRT binding sites between TRPM8 and PI(4,5)P2 suggest a lipid shuttling mechanism between TRPM8 and PIRT as part of the regulatory function. These studies provide the first glimpses of a structural and molecular framework to begin to dissect the regulatory mechanism of the tripartite PIRT–TRPM8–PI(4,5)P2 complex. |
