Opening TRPP2 ( PKD2L1 ) requires the transfer of gating charges

Abstract

The opening of voltage-gated ion channels is initiated by transfer of gating charges that sense the electric field across the membrane. Although transient receptor potential ion channels (TRP) are members of this family, their opening is not intrinsically linked to membrane potential, and they are generally not considered voltage gated. Here we demonstrate that TRPP2, a member of the polycystin subfamily of TRP channels encoded by the PKD2L1 gene, is an exception to this rule. TRPP2 borrows a biophysical riff from canonical voltage-gated ion channels, using 2 gating charges found in its fourth transmembrane segment (S4) to control its conductive state. Rosetta structural prediction demonstrates that the S4 undergoes ∼3- to 5-Å transitional and lateral movements during depolarization, which are coupled to opening of the channel pore. Here both gating charges form state-dependent cation–π interactions within the voltage sensor domain (VSD) during membrane depolarization. Our data demonstrate that the transfer of a single gating charge per channel subunit is requisite for voltage, temperature, and osmotic swell polymodal gating of TRPP2. Taken together, we find that irrespective of stimuli, TRPP2 channel opening is dependent on activation of its VSDs.

Global alignment and assessment of TRP channel transmembrane domain structures to explore functional mechanisms

“…On the sequence level, the pore domains in TRP channels are highly conserved across all TRP channel subfamilies, whereas the peripheral S1-S4 domains are more variable between subfamilies ( Figure 2—figure supplement 1 ; sequence identity data from Fr-TM-Align pairwise alignments not shown) ( Ng et al, 2019 ; Palovcak et al, 2015 ; Vinayagam et al, 2018 ). Consistent with this pattern, clustering of TRP channel structures into subfamilies was more robust when considering the TM-scores of the peripheral S1-S4 domains compared to those of the pore domain ( Figure 2—figure supplements 2 and 3 ).…”

Adaptive selection drives TRPP3 loss-of-function in an Ethiopian population

“…Besides, the comparison of the structures of the wild type and mutant form in open conformation (see Supplementary Fig. S5 online) shows that the connecting helix between S2 and S3 is unfolded, with a movement of helix S4 that orients K455 towards D390 in the wild type, according to 45 . The structural analysis of the models shows a similar distribution of contacts at hydrogen bonding distance (H-bond, considering the maximum acceptable distance to form the hydrogen bond at 3.5 Å), between D390 and K452 and between D390 and K455, for both mutant and wild type forms (see Supplementary Fig.…”

“…During this VSD motion, the negatively charged D390 of S3 segment would stabilize K452 in the closed state and K455 in the open state. Furthermore, Y366 would interact sequentially first with K452 (in the deactivated state) and then with K455 (in the activated state) to provide the required energy for channel opening 45 . This coupling between VSD movement and pore opening seems to be a general mechanism for TRPP3 activation applying also for other physiological stimuli.…”

“…This coupling between VSD movement and pore opening seems to be a general mechanism for TRPP3 activation applying also for other physiological stimuli. Thus, neutralization of one of these two gating charges strongly impairs channel gating regardless of the stimulus employed (voltage, hypoosmotic shock or temperature) 45 .…”

Structural mechanisms of transient receptor potential ion channels

“…For instance, TRPV1 and TRPM8 show apparent gating charges of less than 1 e as compared with 13 e measured for the Shaker K + channel (Schoppa et al, 1992; Voets et al, 2004a; Matta and Ahern, 2007). PKD2L1 represents a notable exception as it retains two gating charges, and channel activation by disparate stimuli all requires transfer of a total of approximately four gating charges (i.e., a single gating charge per subunit; Ng et al, 2019). Nevertheless, the VSLD of most TRP channels, as first observed in TRPV1 (Cao et al, 2013), is rigid and remains static during channel gating.…”