The mechanism of activation of the transient receptor potential vanilloid 4 (TRPV4) channel by 4alpha-phorbol esters was investigated by combining information from chemical modification of 4alpha-phorbol-didecanoate (4alpha-PDD, 2a), site-directed mutagenesis, Ca(2+) imaging, and electrophysiology. Binding of 4alpha-phorbol esters occurs in a loop in the TM3-TM4 domain of TRPV4 that is analogous to the capsaicin binding site of TRPV1, and the ester decoration of ring C and the A,B ring junction are critical for activity. The lipophilic ester groups on ring C serve mainly as a steering element, affecting the orientation of the diterpenoid core into the ligand binding pocket, while the nature of the A,B ring junction plays an essential role in the Ca(2+)-dependence of the TRPV4 response. Taken together, our results show that 4alpha-phorbol is a useful template to investigate the molecular details of TRPV4 activation by small molecules and obtain information for the rational design of structurally simpler ligands for this ion channel.

No abstract

The ligand deorphanization of TRP channels has a tremendous potential for biomedical and nutritional research, and this review highlights the role that natural products have played in the identification of ligands for these targets and their establishment as viable candidates for drug discovery. Specific ligands have so far been discovered only for some thermoTRPs, like TRPV1, TRPV3, TRPV4, TRPM8 and TRPA1, and the lack of selective pharmacology has been a major drawback for unraveling the biological role of TRPs. While genetic approaches (transgenic animal models) have partially compensate for the lack of ligands, the universal expression of TRPs in living systems and the success achieved with TRPV1 suggest that a systematic investigation of the natural products pool might alleviate this shortage, fostering adoption by small molecules within this class of still largely orphan biological targets.

No abstract