# Distinct Properties of $$Ca^{2+}$$-Calmodulin Binding to N- and C-Terminal Regulatory Regions of the TRPV1 Channel

 Title: Distinct Properties of $$Ca^{2+}$$-Calmodulin Binding to N- and C-Terminal Regulatory Regions of the TRPV1 Channel Author: Gaudet, Rachelle; Lau, Sze-Yi; Procko, Erik Note: Order does not necessarily reflect citation order of authors. Citation: Lau, Sze-Yi, Erik Procko, and Rachelle Gaudet. 2012. Distinct properties of $$Ca^{2+}$$-calmodulin binding to N- and C-terminal regulatory regions of the TRPV1 channel. Journal of General Physiology 140(5): 541-555. Full Text & Related Files: Gaudet_Distinct.pdf (1.109Mb; PDF) Abstract: Transient receptor potential (TRP) vanilloid 1 (TRPV1) is a molecular pain receptor belonging to the TRP superfamily of nonselective cation channels. As a polymodal receptor, TRPV1 responds to heat and a wide range of chemical stimuli. The influx of calcium after channel activation serves as a negative feedback mechanism leading to TRPV1 desensitization. The cellular calcium sensor calmodulin (CaM) likely participates in the desensitization of TRPV1. Two CaM-binding sites are identified in TRPV1: the N-terminal ankyrin repeat domain (ARD) and a short distal C-terminal (CT) segment. Here, we present the crystal structure of calcium-bound CaM $$(Ca^{2+}–CaM)$$ in complex with the TRPV1-CT segment, determined to $$1.95-\mathring{A}$$ resolution. The two lobes of $$Ca^{2+}–CaM$$ wrap around a helical TRPV1-CT segment in an antiparallel orientation, and two hydrophobic anchors, W787 and L796, contact the C-lobe and N-lobe of $$Ca^{2+}–CaM$$, respectively. This structure is similar to canonical $$Ca^{2+}–CaM$$-peptide complexes, although TRPV1 contains no classical CaM recognition sequence motif. Using structural and mutational studies, we established the TRPV1 C terminus as a high affinity $$Ca^{2+}–CaM$$-binding site in both the isolated TRPV1 C terminus and in full-length TRPV1. Although a ternary complex of CaM, TRPV1-ARD, and TRPV1-CT had previously been postulated, we found no biochemical evidence of such a complex. In electrophysiology studies, mutation of the $$Ca^{2+}–CaM$$-binding site on TRPV1-ARD abolished desensitization in response to repeated application of capsaicin, whereas mutation of the $$Ca^{2+}–CaM$$-binding site in TRPV1-CT led to a more subtle phenotype of slowed and reduced TRPV1 desensitization. In summary, our results show that the TRPV1-ARD is an important mediator of TRPV1 desensitization, whereas TRPV1-CT has higher affinity for CaM and is likely involved in separate regulatory mechanisms. Published Version: doi:10.1085/jgp.201210810 Other Sources: http://www.ncbi.nlm.nih.gov/pubmed/23109716 Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10860184 Downloads of this work: