Structure of the thermo-sensitive TRP channel TRP1 from the alga Chlamydomonas reinhardtii

Abstract

Algae produce the largest amount of oxygen on earth and are invaluable for human nutrition and biomedicine, as well as for the chemical industry, energy production and agriculture. The mechanisms by which algae can detect and respond to changes in their environments can rely on membrane receptors, including TRP ion channels. Here we present a 3.5-Å resolution cryo-EM structure of the transient receptor potential (TRP) channel crTRP1 from the alga Chlamydomonas reinhardtii that opens in response to increased temperature and is positively regulated by the membrane lipid PIP₂. The structure of crTRP1 significantly deviates from the structures of other TRP channels and has a unique 2-fold symmetrical rose-shape architecture with elbow domains and ankyrin repeat domains submerged and dipping into the membrane, respectively. Our study provides a structure of a TRP channel from a micro-organism and a structural framework for better understanding algae biology and TRP channel evolution.

Fig. 1

Functional characterization of crTRP1. a Representative single-channel recordings of crTRP1 currents obtained in the absence of phosphoinositides or in the presence of 2.5 µM PIP₂ at 28 °C and +120 mV (n = 5; the number of events analyzed (NE) = 2538) or PI(4)P at 28 °C and +100 mV (n = 3; NE = 650). b Current–voltage (I–V) relationship for crTRP1 activity evoked by 2.5 µM PIP₂ at 28 °C. The data represent 15 independent experiments, NE = 114,629. c Representative single-channel traces obtained from voltage ramps of −100 to +100 mV (representative of n = 8). d crTRP1 channel open probability (P_o) obtained at 22 and 28 °C, and two different voltages, −100 and +100 mV (n = 18; NE = 192,809). e Representative crTRP1 current traces obtained in the presence of 2.5 µM PIP₂ in response to a temperature increase from 22 to 28 °C, at −100 and +100 mV (representative of n = 15). f Temperature dependence of P_o in the presence of 2.5 µM PIP₂, obtained at +100 mV (n = 12; NE = 67,673). Insert, Q₁₀ was estimated from the regression slope of temperature dependent changes in P_o, Q₁₀ = 25.5 ± 1.2. g Representative crTRP1 current traces recorded at 28 °C, +120 mV, and 2.5 µM PIP₂ (upper traces), in the presence of 1.9 mM GdCl₃ (middle traces), or 10 µM BCTC (lower traces). h Summary of crTRP1 inhibition by 1.9 mM GdCl₃ or 10 µM BCTC (n = 3 for each inhibitor, NE = 8,560; difference in P_o values was calculated using One-way ANOVA, p = 1.6 × 10⁻⁵ for the control vs. GdCl₃, and p = 1.7 × 10⁻⁵ for the control vs. BCTC). All data are presented as mean ± SEM. Source data are provided as a Source Data file

Fig. 2

Architecture and domain organization of crTRP1. a–c Two side (a, b) and top (c) views of the crTRP1 tetramer, with each subunit shown in a different color. d Domain organization diagram of a crTRP1 subunit. e, f Two views of a crTRP1 subunit, with domains colored as in d

Fig. 3

Comparison of the domain organizations of different TRP channels. a Linear domain topologies for different TRP channel subtypes aligned relative to the transmembrane domain with structural architectures illustrated by zebrafish TRPM2 (PDB ID: 6DRJ), human TRPM4 (PDB ID: 6BQV), alga crTRP1, mouse TRPC4 (PDB ID: 5Z96), mouse TRPV3 (PDB ID: 6DVY), human TRPV6 (PDB ID: 6B08), human TRPA1 (PDB ID: 3J9P), drosophila TRPN (PDB ID: 5VKQ), human PKD2 (PDB ID: 5T4D), and marmoset TRPML3 (PDB ID: 5W3S). b Structures of crTRP1 (left) and mouse TRPC4 (right, PDB ID: 5Z96) viewed parallel to membrane and illustrating different positioning of the ARDs (orange) relative to membrane (gray horizontal lines)

Fig. 4

Surface electrostatics, central pore and portals. a, b Side (a) and top (b) views of crTRP1 structure in surface representation, colored by electrostatic potential. c, d Central slices of crTRP1 surface through the upper (c) and the lower (d) portals in the directions indicated by the dotted lines in b

Fig. 5

Auxiliary lipids. a, b, Side (a) and top (b) views of the crTRP1 tetramer, with each subunit shown in a different color and putative lipid densities 1–4 illustrated by purple mesh. c, d Expanded views of lipid densities 1 (c) and 2–3 (d). Molecules of PIP₂ and PC fitted in densities 1–2 and 3, respectively; the surrounding residues are shown as sticks

Fig. 6

Twofold symmetry and pore. a, b Extracellular (a) and intracellular (b) views of the crTRP1 tetramer with pairs of diagonal subunits A/C and B/D colored green and yellow, respectively. Cα atoms of A74, L741, and L871 are shown as dark spheres connected by lines. c Superposition of subunits A and B, with lipid molecules shown in space-filling representation. Relative displacements of the S5 and coiled coil helices and rotation of S6 are indicated by red arrows. d, e Pore-forming regions in subunits A/C (d) and B/D (e), with S6 residues shown as sticks and putative lipid density 4 illustrated by purple mesh. f The pore radius (excluding P-loop region) calculated using HOLE

Fig. 7

Membrane-linked sensory domains. a Side view of crTRP1 tetramer in nanodisc, with two of four pre-S1 elbows colored green, two of four post-TRP elbows colored purple, two of four ARDs colored orange and the rest of the molecule colored cyan. Cryo-EM density is shown as gray mesh; the membrane boundaries are indicated by horizontal lines. b Top view of subunit A’s elbows; residues facing the membrane are shown as sticks. c Side view of the ARD from subunit D; residues in proximity to the intracellular membrane boundary (horizontal line) are shown as sticks. d Cartoon illustrating possible gating mechanism that involves lipids (PIP₂ in red and PC in dark blue) and that transmits changes in the membrane environment from the ARD and elbow domains through the TRP helices to the S6 gate