Cryo-EM structure of the receptor-activated TRPC5 ion channel at 2.9 angstrom resolution

Abstract

32The transient receptor potential canonical subfamily member 5 (TRPC5) is a 33 non-selective calcium-permeant cation channel. As a depolarizing channel, its function 34 is studied in the central nervous system and kidney. TRPC5 forms heteromultimers 35 with TRPC1, but also forms homomultimers. It can be activated by reducing agents 36 through reduction of the extracellular disulfide bond. Here we present the 2.9 Å 37 resolution electron cryo-microscopy (cryo-EM) structure of TRPC5. The structure of 38 TRPC5 in its apo state is partially open, which may be related to the weak activation of 39 TRPC5 in response to extracellular pH. We also report the conserved negatively charged 40 residues of the cation binding site located in the hydrophilic pocket between S2 and S3. 41Comparison of the TRPC5 structure to previously determined structures of other TRPC 42 and TRP channels reveals differences in the extracellular pore domain and in the 43 length of the S3 helix. Together, these results shed light on the structural features that 44 contribute to the specific activation mechanism of the receptor-activated TRPC5. 45 46 47 48 65 Results 66Overall structure of the mouse TRPC5 tetrameric ion channel 67 A mouse TRPC5 construct lacking the C-terminal 210 residues (a.a. 1-765, excluding a.a. 68 766-975) yielded more protein after purification than that of the full-length construct. The 69 baculovirus construct, consisting of a maltose binding protein (MBP) tag at the N 70 terminus, was stably purified to homogeneity in n-dodecyl β-D-maltoside (DDM) and 71 reconstituted in the amphipol poly (maleic anhydride-alt-1-decene) substituted with 72 3-(dimethylamino) propylamine (PMAL-C8; Supplementary Fig. 1). The amphipol 73 reconstituted detergent-free protein was then negatively stained and analyzed by 74 single-particle cryo-EM. 75Single particle cryo-EM analyses of TRPC5 at an overall resolution of ~ 2.9 Å was 76 sufficient for de novo model building (Supplementary Fig. 2, Supplementary Fig. 3, 77 Supplementary Table 1). Disordered regions led to poor densities for 7 residues in the 78 S1-S2 loop, 28 residues in the distal N terminus, and 3 residues in the truncated distal C 79 terminus. Similar to other solved TRP channel structures, TRPC5 forms a four-fold 80 symmetric homotetramer (Fig. 1a, b) with dimensions of 100 Å × 100 Å × 120 Å. 81Each of the four monomers can be divided into a compact cytosolic domain and a 82 transmembrane domain (TMD) (Fig. 1). The cytosolic domain is composed of the 83 N-terminal region with an ankyrin repeats domain (ARD) and seven α-helices (HLH); 84 the C-terminal subdomain contains a connecting helix and a coiled-coil domain. The 85 transmembrane domain (TMD) is composed of six α-helices (S1-S6), a TRP domain, and 315We thank Dr. Steve Harrison and the Cryo-EM Facility (Harvard Medical School) for use 316 of their microscopes. We thank Dr. Maofu Liao for providing the Python scripts and help in 317

TRP ion channels: Proteins with conformational flexibility

“…However, the TRPC5 is considered at least partially open since the constriction at the lower gate formed by the residues I621, N625 and Q629 was around 4.9 Å [120]. Comparing this structure with the closed TRPC4, Duan and collaborators suggest that the extracellular disulfide bond is a transducer of conformational changes.…”

“…Until just recently, finely defined structural characteristics of TRPC channels have remained elusive, mainly because of the lack of high-resolution structures. The cryo-EM structures obtained to date are those for the TRPC3, TRPC4, TRPC5 and TRPC6 channels [118][119][120][121][122][123]. However, no functional studies reporting changes in the conductance of these channels in response to different agonists are available.…”

“…The second group includes the TRPC4/C5 channels that are modulated by G q, G i/o GPCRs, membrane lipids, and intracellular Ca 2+ [119,125]. These channels share the common feature of a disulfide bond between two cysteines at the loop linking S5 and the pore domain that maintains the residue E555 in proper position and thus stabilize the upper region of their selectivity filters [119,120,123,124]. As in other TRP channels, the TRP domain of TRPC4 is an important molecular effector for gating in this protein since it interacts with the S4-S5 linker and other proteins [123].…”

What is new about mild temperature sensing? A review of recent findings

“…Among the TRPC channels, TRPC5 has been shown to be highly sensitive to mild cooling in the range from 37°C to 25°C in DRG neurons in mice, also it is known that it is present in human tissues [28]. The structure of TRPC5 was obtained by cryo-EM at 2.9 Å resolution, however the PDB is not available yet [19]. A hypothesis regarding why TRPC5 does not seem to be an important ion channel for thermosensation is that deleting TRPC5, in the mouse, results in compensatory replacement by functionally overlapping cold transducers.…”

“…The regions with the largest structural divergences are the intracellular domains. While TRPV channels are almost structurally identical [3,[5][6][7][8][9][10][11] and share homology with TRPA1 [12], the TRPM and TRPC channels have amino and carboxy-termini with very different topology [13][14][15][16][17][18][19] (Figure 1). The thermoTRP channels are a subgroup of 11 members of the TRPA, TRPV, TRPC, and TRPM subfamilies.…”