Proton currents constrain structural models of voltage sensor activation

Abstract

The Hv1 proton channel is evidently unique among voltage sensor domain proteins in mediating an intrinsic ‘aqueous’ H+ conductance (GAQ). Mutation of a highly conserved ‘gating charge’ residue in the S4 helix (R1H) confers a resting-state H+ ‘shuttle’ conductance (GSH) in VGCs and Ci VSP, and we now report that R1H is sufficient to reconstitute GSH in Hv1 without abrogating GAQ. Second-site mutations in S3 (D185A/H) and S4 (N4R) experimentally separate GSH and GAQ gating, which report thermodynamically distinct initial and final steps, respectively, in the Hv1 activation pathway. The effects of Hv1 mutations on GSH and GAQ are used to constrain the positions of key side chains in resting- and activated-state VS model structures, providing new insights into the structural basis of VS activation and H+ transfer mechanisms in Hv1.DOI: http://dx.doi.org/10.7554/eLife.18017.001

CrossTalk opposing view: proton transfer in Hv1 utilizes a water wire, and does not require transient protonation of a conserved aspartate in the S1 transmembrane helix

“…; Randolph et al . ). Here we summarize evidence supporting the latter hypothesis, which is depicted in cartoon form in Fig.…”

“…Side chains of selected residues are shown in stick representation (colour‐coded by atom type: carbon, cyan; nitrogen, blue; oxygen, red; hydrogens, white; H atoms are omitted for clarity in left and centre panels), and indicated by labels (red, D112/D 1.51 ; cyan, R205H/R 4.47 H/R1H; blue, R211/R 4.53 /R3; green, N214/N 4.56 /N4; grey, F150/F 2.50 ); residue numbering is as described previously (Randolph et al . ). Water molecules in the Hv1 E system are shown in CPK representation coloured by atom type (red, oxygen; white, hydrogen); waters are omitted for clarity in the centre and right panels.…”

“…) activated state (centre and right panels) and Hv1 E (Randolph et al . ) R1H resting state (centre and left panels) systems show magnified side views of Hv1 VS domain model structures in isolation and in overlay (MultiSeq STAMP structural alignment, VMD 1.9.3; http://www.ks.uiuc.edu). Helical segments are represented as coloured ribbons (S1, yellow; S2, green; S3, blue; S4, red), except where omitted for clarity (centre and right panels).…”

The acid test for pH-dependent gating in cloned HV1 channels

“…Voltage-gated proton channels play important roles in intracellular pH regulation, immune cell responses, sperm motility, and mucus secretion in epithelia, to name just a few of their functions (DeCoursey, 2013). These curious proteins were given a molecular identity when Ramsey et al (2006) and Sasaki et al (2006) cloned the human and mouse H V 1 proteins, respectively.The H V 1 protein has the same structural fold as voltage-sensing domains (VSDs) found in classic or canonic voltage-gated ion channels (Takeshita et al, 2014;Randolph et al, 2016). The proton channel, at least in humans, is formed by a dimer of two VSDs.…”

“…The H V 1 protein has the same structural fold as voltage-sensing domains (VSDs) found in classic or canonic voltage-gated ion channels (Takeshita et al, 2014;Randolph et al, 2016). The proton channel, at least in humans, is formed by a dimer of two VSDs.…”