Transient receptor potential (TRP) ion channels form heteromers through combinatorial associations of distinct subunits, contributing to the diversity of TRP channel functions. Among them, TRPC5, which forms a heteromer with TRPC1, represents an attractive pharmaceutical target for treating anxiety and depression. Here, we present the cryo-electron microscopy structure of the human TRPC1/C5 heteromer, composed of one TRPC1 subunit and three TRPC5 subunits. The incorporation of TRPC1 into the heteromer disrupts the C4 symmetry of the TRPC5 homotetramer, resulting in a distinct ion conduction pathway characterized by an asymmetrically constricted selectivity filter and an asymmetric lower gate. The TRPC1/C5 heteromer displays recognizable structural features compared to the TRPC1/C4 heteromer, including a noncanonically tilted coiled-coil domain and a distinct intersubunit interactions. Furthermore, we elucidate the structures of human TRPC5 bound to the TRPC1/4/5-specific agonist, (-)-Englerin A. Our findings establish a foundation for exploring the diversity of heteromeric TRP channels and pave the way for targeting TRPC1/C5 as a therapeutic strategy.

Transient receptor potential (TRP) ion channels have a crucial role as cellular sensors, mediating diverse physical and chemical stimuli. The formation of heteromeric structures expands the functionality of TRP channels; however, their molecular architecture remains largely unknown. Here we present the cryo-electron microscopy structures of the human TRPC1/TRPC4 heteromer in the apo and antagonist-bound states, both consisting of one TRPC1 subunit and three TRPC4 subunits. The heteromer structure reveals a distinct ion-conduction pathway, including an asymmetrically constricted selectivity filter and an asymmetric lower gate, primarily attributed to the incorporation of TRPC1. Through a structure-guided electrophysiological assay, we show that both the selectivity filter and the lower part of the S6 helix participate in deciding overall preference for permeating monovalent cations. Moreover, we reveal that the introduction of one lysine residue of TRPC1 into the tetrameric central cavity is enough to render one of the most important functional consequences of TRPC heteromerization: reduced calcium permeability. Our results establish a framework for addressing the structure-function relationship of the heteromeric TRP channels. Here the authors present the cryo-EM structures of heteromeric TRPC1/TRPC4 channel and provide structure-function insights into its heteromer-specific properties.

G-protein coupled receptors (GPCRs) and ion channels serve as key molecular switches through which extracellular stimuli are transformed into intracellular effects, and it has long been postulated that ion channels are direct effector molecules of the alpha subunit of G-proteins (Gα). However, no complete structural evidence supporting the direct interaction between Gα and ion channels is available. Here, we present the cryo-electron microscopy structures of the human transient receptor potential canonical 5 (TRPC5)-Gα i3 complexes with a 4:4 stoichiometry in lipid nanodiscs. Remarkably, Gα i3 binds to the ankyrin repeat edge of TRPC5 ~ 50 Å away from the cell membrane. Electrophysiological analysis shows that Gα i3 increases the sensitivity of TRPC5 to phosphatidylinositol 4,5-bisphosphate (PIP 2 ), thereby rendering TRPC5 more easily opened in the cell membrane, where the concentration of PIP 2 is physiologically regulated. Our results demonstrate that ion channels are one of the direct effector molecules of Gα proteins triggered by GPCR activation–providing a structural framework for unraveling the crosstalk between two major classes of transmembrane proteins: GPCRs and ion channels.

Transient receptor potential vanilloid member 3 (TRPV3) is an ion channel that plays a critical role in temperature sensing in skin. There have been active studies on how TRPV3, which is also known as one of the temperature-sensitive transient receptor potential (thermoTRP) channels, responds to temperature. However, the previous studies were mostly based on TRPV3 originating from mice or rats. Here, we focus on human TRPV3 (hTRPV3) and show that which domain of hTRPV3 undergoes conformational changes as temperature increases by Förster resonance energy transfer (FRET) assay. During the heat-induced activation of hTRPV3, the linker domain close to C-terminus, that is, the C-terminal domain shows a largest structural change whereas there is little change in the ankyrin repeat domain (ARD). Interestingly, the activation of hTRPV3 by an agonist shows structural change patterns that are completely different from those observed during activation by heat; we observe structural changes in ARD and S2–S3 linker after ligand stimulation whereas relatively little change is observed when stimulated by heat. Our results provide insight into the thermal activation of hTRPV3 channel.

In eukaryotic cells, organelles are distributed and positioned in proximity to each other through molecular tether proteins. Among these, the mitochondria-endoplasmic reticulum cortex anchor (MECA) is a well-known tethering complex in Saccharomyces cerevisiae that tethers mitochondria to the plasma membrane and plays a key role in mitochondrial fission. The main components of MECA are Num1 and Mdm36, and it is known that Mdm36 binds to Num1 to enhance mitochondrial tethering. To better understand the biochemical characteristics of the Num1-Mdm36 complex at the molecular level, we purified the coiled-coil domain of Num1, full-length Mdm36, and Num1-Mdm36 complex and identified the oligomeric state and stoichiometric characteristics of the Num1-Mdm36 complex by chemical crosslinking, size-exclusion chromatography coupled with multi-angle light scattering, and isothermal titration calorimetry. Mdm36 exists as a dimer and interacts preferentially with Num1 with a stoichiometry of 2:2, forming a heterotetrameric complex. Furthermore, we narrowed down the specific binding region of Num1, which is essential for interacting with Mdm36, and showed that their binding affinity is strong enough to tether both mitochondrial and plasma membranes. Our biochemical characterizations suggest a stoichiometric model of the Num1-Mdm36 complex at the mitochondria-plasma membrane contact site in budding yeast.