1) Heat activation is intrinsic to the pore domain of TRPV1 The TRPV1 channel is a sensitive detector of pain-producing stimuli,including noxious heat, acid, inflammatory mediators, and vanilloid compounds. Although binding sites for some activators have been identified, the location of the temperature sensor remains elusive. Using available structures of TRPV1 and voltage-activated potassium channels, we engineered chimeras wherein transmembrane regions of TRPV1were transplanted into the Shaker Kv channel. Here we show that transplanting the pore domain of TRPV1 into Shaker gives rise to functional channels that can be activated by a TRPV1-selective tarantula toxin that binds to the outer pore of the channel. This pore-domain chimera is permeable to Na+, K+, and Ca2+ ions, and remarkably, is also robustly activated by noxious heat. Our results demonstrate that the pore of TRPV1 is a transportable domain that contains the structural elements sufficient for activation by noxious heat. 2) Single-particle cryo-EM structure of a voltage-activated potassium channel in lipid nanodiscs Voltage-activated potassium (Kv) channels open to conduct K+ ions in response to membrane depolarization, and subsequently enter non-conducting states through distinct mechanisms of inactivation. X-ray structures of detergent-solubilized Kv channels appear to have captured an open state even though a non-conducting C-type inactivated state would predominate in membranes in the absence of a transmembrane voltage. However, structures for a voltage-activated ion channel in a lipid bilayer environment have not yet been reported. Here we report the structure of the Kv1.22.1 paddle chimera channel reconstituted into lipid nanodiscs using single-particle cryo-electron microscopy. At a resolution of 3 A for the cytosolic domain and 4 A for the transmembrane domain, the structure determined in nanodiscs is similar to the previously determined X-ray structure. Our findings show that large differences in structure between detergent and lipid bilayer environments are unlikely, and enable us to propose possible structural mechanisms for C-type inactivation. 3) Structural relationship between the putative hair cell mechanotransduction channel TMC1 and TMEM16 proteins The hair cell mechanotransduction (MET) channel complex is essential for hearing, yet its molecular identity and structure remain elusive. The transmembrane channellike 1 (TMC1) protein localizes to the site of the MET channel, interacts with the tip-link responsible for mechanical gating, and genetic alterations in TMC1 alter MET channel properties and cause deafness, supporting the hypothesis that TMC1 forms the MET channel. We generated a model of TMC1 based on X-ray and cryo-EM structures of TMEM16 proteins, revealing the presence of a large cavity near the protein-lipid interface that also harbors the Beethoven mutation, suggesting that it could function as a permeation pathway. We also find that hair cells are permeable to 3 kDa dextrans, and that dextran permeation requires TMC1/2 proteins and functional MET channels, supporting the presence of a large permeation pathway and the hypothesis that TMC1 is a pore forming subunit of the MET channel complex.
| Ballesteros, Angela; Swartz, Kenton J (2018) Lipids surf the groove in scramblases. Proc Natl Acad Sci U S A 115:7648-7650 |
| Ballesteros, Angela; Fenollar-Ferrer, Cristina; Swartz, Kenton Jon (2018) Structural relationship between the putative hair cell mechanotransduction channel TMC1 and TMEM16 proteins. Elife 7: |
| Bae, Chanhyung; Jara-Oseguera, Andres; Swartz, Kenton J (2018) TRPM channels come into focus. Science 359:160-161 |
| Matthies, Doreen; Bae, Chanhyung; Toombes, Gilman Es et al. (2018) Single-particle cryo-EM structure of a voltage-activated potassium channel in lipid nanodiscs. Elife 7: |
| Zhang, Feng; Jara-Oseguera, Andres; Chang, Tsg-Hui et al. (2018) Heat activation is intrinsic to the pore domain of TRPV1. Proc Natl Acad Sci U S A 115:E317-E324 |
| Chavan, Tanmay; Maduke, Merritt; Swartz, Kenton (2017) Protein ligands for studying ion channel proteins. J Gen Physiol 149:407-411 |
| Toombes, Gilman E S; Swartz, Kenton J (2016) STRUCTURAL BIOLOGY. Twists and turns in gating ion channels with voltage. Science 353:646-7 |
| Jara-Oseguera, Andres; Bae, Chanhyung; Swartz, Kenton J (2016) An external sodium ion binding site controls allosteric gating in TRPV1 channels. Elife 5: |
| Bae, Chanhyung; Anselmi, Claudio; Kalia, Jeet et al. (2016) Structural insights into the mechanism of activation of the TRPV1 channel by a membrane-bound tarantula toxin. Elife 5: |
| Zhang, Feng; Hanson, Sonya M; Jara-Oseguera, Andres et al. (2016) Engineering vanilloid-sensitivity into the rat TRPV2 channel. Elife 5: |
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