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PreprintCited by 0Ion channel regulation and functionAdvanced Fluorescence Microscopy TechniquesProtein Structure and Dynamics

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Interrogating the structure and function of the human voltage-gated proton channel (hHv1) with a fluorescent noncanonical amino acid

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Carmona, Emerson M., Zagotta, William N., Gordon, Sharona E.·2025·eLife
DOI 10.1101/2025.10.23.684235PMC PMC12633253

Preprint — published as 10.7554/elife.110161.3 · Paper page

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Abstract

The human voltage-gated proton channel (hH v 1) is a dimer of voltage-sensor domains (VSDs) containing highly selective proton permeation pathways in each monomer. In addition to voltage, hH v 1 is regulated by other stimuli, including pH gradients, mechanical forces, and ligands such as Zn 2+ . Aside from the VSDs, this membrane protein contains an N-terminal domain and a C-terminal coiled-coil domain (CC) formed between the monomers. To address the need for direct measurements of conformational rearrangements in hH v 1, we developed a Förster resonance energy transfer (FRET) approach to measuring the conformational rearrangements in full-length hH v 1 purified from E. coli . We used genetic code expansion (GCE) to generate a library of 14 full-length hH v 1 constructs, each incorporating the fluorescent noncanonical amino acid acridon-2-ylalanine (Acd) at a different site throughout the various structural domains. Following the expression and purification of these hH v 1-Acd proteins, we found that 12 sites yielded stable and functional proton-permeable channels. The fluorescence properties of Acd at each site showed small site-specific differences. Furthermore, we measured site-specific FRET efficiencies from tryptophan (Trp) and tyrosine (Tyr) to Acd in the hH v 1-Acd proteins and found results consistent with correct folding in detergent micelles. Finally, the addition of Zn 2+ produced reversible changes in FRET, with affected residues clustered on the intracellular side of the channel.

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Figures

Figure 1. hHv1 was labeled with the fluorescent noncanonical amino acid Acd by genetic code expansion. (A) Cartoon showing the components of the genetic code expansion system used to incorporate Acd via amber codon suppression in hHv1. (B) AlphaFold structural model of the dimer hHv1 colored by subunit. (C) AlphaFold structural model of a single hHv1 subunit colored by the predicted Local Distance Difference Test (pLDDT). Model confidence was represented by a gradient from red to blue, indicating low to high pLDDT. (D) In-gel fluorescence and Western blot to evaluate Acd incorporation. An Acd fluorescence band corresponding to the molecular weight of full-length hHv1 (red arrow) was observed in cellular extracts after separation by SDS-PAGE only when cells contained the MjA9-AcdRS/tRNA plasmid (RS) and were grown in the presence of 1mM Acd (top). The Western blot against the His-tag present at the N-terminus of hHv1 confirmed that the band corresponded to the recombinant protein (bottom). Note the hHv1 truncated product produced when the amber stop codon is replacing F247 in the absence of the aminoacyl-tRNA synthetase/tRNA plasmid and Acd.
Figure 1. hHv1 was labeled with the fluorescent noncanonical amino acid Acd by genetic code expansion. (A) Cartoon showing the components of the genetic code expansion system used to incorporate Acd via amber codon suppression in hHv1. (B) AlphaFold structural model of the dimer hHv1 colored by subunit. (C) AlphaFold structural model of a single hHv1 subunit colored by the predicted Local Distance Difference Test (pLDDT). Model confidence was represented by a gradient from red to blue, indicating low to high pLDDT. (D) In-gel fluorescence and Western blot to evaluate Acd incorporation. An Acd fluorescence band corresponding to the molecular weight of full-length hHv1 (red arrow) was observed in cellular extracts after separation by SDS-PAGE only when cells contained the MjA9-AcdRS/tRNA plasmid (RS) and were grown in the presence of 1mM Acd (top). The Western blot against the His-tag present at the N-terminus of hHv1 confirmed that the band corresponded to the recombinant protein (bottom). Note the hHv1 truncated product produced when the amber stop codon is replacing F247 in the absence of the aminoacyl-tRNA synthetase/tRNA plasmid and Acd.CC BY · PubMed Central
Figure 2. Acd was incorporated into 14 positions in the hHv1 sequence. (A) Cartoon showing the amino acids selected to be replaced by an amber stop codon in the hHv1 secondary structure to incorporate Acd (stars). (B) AlphaFold dimer hHv1 structural model with the amino acids selected to be replaced by Acd as cyan spheres. (C) Acd fluorescence gel (top) and Western blot (bottom) of cellular extracts after separation by SDS-PAGE showing the expression of the Acd-labeled hHv1 mutants. The No TAG lane contains an extract from cells grown under identical conditions (in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair) and expressing hHv1 without an amber stop codon.
Figure 2. Acd was incorporated into 14 positions in the hHv1 sequence. (A) Cartoon showing the amino acids selected to be replaced by an amber stop codon in the hHv1 secondary structure to incorporate Acd (stars). (B) AlphaFold dimer hHv1 structural model with the amino acids selected to be replaced by Acd as cyan spheres. (C) Acd fluorescence gel (top) and Western blot (bottom) of cellular extracts after separation by SDS-PAGE showing the expression of the Acd-labeled hHv1 mutants. The No TAG lane contains an extract from cells grown under identical conditions (in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair) and expressing hHv1 without an amber stop codon.CC BY · PubMed Central
Figure 3. Purification and functional measurements of hHv1-Acd proteins. (A) Coomassie-stained (top) and Acd fluorescence (bottom) gels after separation by SDS-PAGE showing representative samples of the membrane extracts after solubilization (left) and the final purified protein after immobilized metal affinity chromatography (right). (B) Protein yield of the hHv1 protein with Acd replacing the amino acid at the indicated position. Note that V187Acd and Q233Acd contained no detectable protein after purification. The red line indicates the protein yield obtained from hHv1 without an amber stop codon in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair (No TAG). (C) Representative fluorescence-detection size-exclusion chromatograms of the purified hHv1 proteins with Acd incorporated at the indicated amino acid position. Insets: AlphaFold dimer models, with the amino acid replaced by Acd shown as cyan spheres. (D) Representative liposome proton flux assay of asolectin proteoliposomes containing the indicated hHv1 protein. All purified proteins produced ACMA fluorescence quenching after the addition of valinomycin (Val). The protonophore CCCP was added at the end of the experiment as a control. The No TAG sample corresponds to proteoliposomes containing hHv1 without an amber stop codon expressed in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair.
Figure 3. Purification and functional measurements of hHv1-Acd proteins. (A) Coomassie-stained (top) and Acd fluorescence (bottom) gels after separation by SDS-PAGE showing representative samples of the membrane extracts after solubilization (left) and the final purified protein after immobilized metal affinity chromatography (right). (B) Protein yield of the hHv1 protein with Acd replacing the amino acid at the indicated position. Note that V187Acd and Q233Acd contained no detectable protein after purification. The red line indicates the protein yield obtained from hHv1 without an amber stop codon in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair (No TAG). (C) Representative fluorescence-detection size-exclusion chromatograms of the purified hHv1 proteins with Acd incorporated at the indicated amino acid position. Insets: AlphaFold dimer models, with the amino acid replaced by Acd shown as cyan spheres. (D) Representative liposome proton flux assay of asolectin proteoliposomes containing the indicated hHv1 protein. All purified proteins produced ACMA fluorescence quenching after the addition of valinomycin (Val). The protonophore CCCP was added at the end of the experiment as a control. The No TAG sample corresponds to proteoliposomes containing hHv1 without an amber stop codon expressed in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair.CC BY · PubMed Central
Figure 4. Acd showed a low environmental sensitivity in hHv1. (A) Normalized fluorescence emission spectra of the Acd amino acid dissolved in the indicated solvent (Excitation = 370 nm). EtAc: ethyl acetate, OctOH: 1-octanol, ButOH: 1-butanol, EtOH: ethanol. (B) Normalized fluorescence decay of the Acd amino acid dissolved in the indicated solvent. (C) Normalized fluorescence emission spectra of the hHv1-Acd proteins in Buffer-H2 (grey). The Acd amino acid spectra in selected solvents are also shown for reference. Q56Acd and C107Acd spectra are shown with broken lines. The emission maxima are listed in Table S3. (D) Normalized fluorescence decay of the hHv1-Acd proteins in Buffer-H2 (grey). The Acd amino acid decays in selected solvents are also shown for reference. Q56Acd and C107Acd decays are shown in red and black, respectively.
Figure 4. Acd showed a low environmental sensitivity in hHv1. (A) Normalized fluorescence emission spectra of the Acd amino acid dissolved in the indicated solvent (Excitation = 370 nm). EtAc: ethyl acetate, OctOH: 1-octanol, ButOH: 1-butanol, EtOH: ethanol. (B) Normalized fluorescence decay of the Acd amino acid dissolved in the indicated solvent. (C) Normalized fluorescence emission spectra of the hHv1-Acd proteins in Buffer-H2 (grey). The Acd amino acid spectra in selected solvents are also shown for reference. Q56Acd and C107Acd spectra are shown with broken lines. The emission maxima are listed in Table S3. (D) Normalized fluorescence decay of the hHv1-Acd proteins in Buffer-H2 (grey). The Acd amino acid decays in selected solvents are also shown for reference. Q56Acd and C107Acd decays are shown in red and black, respectively.CC BY · PubMed Central
Figure 5. Spectral FRET analysis using Trp and Tyr donors and Acd as acceptor. (A) Fluorescence emission spectra of the intrinsic fluorescent amino acids Trp (black) and Tyr (black, broken lines), along with the Acd absorption spectrum in Buffer-H2 (blue). (B) AlphaFold dimer hHv1 structural model with the amino acids colored according to (C) and the native tryptophan and tyrosine residues shown as yellow spheres. (C) Normalized fluorescence spectra of the purified hHv1-Acd proteins (Excitation = 280 nm). The spectra were normalized by the Trp/Tyr fluorescence. The colors correspond to the indicated hHv1-Acd protein, and the remaining spectra are shown as grey traces in the figure. The No TAG sample (black) contains purified hHv1 protein without any amber stop codon expressed in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair. (D) Example of the spectral FRET analysis procedure. The fluorescence spectrum of hHv1-Y134Acd obtained when exciting at 280 nm (black, F280) minus the normalized spectrum at the same excitation wavelength of the No TAG sample (grey, F280,NoTAG) produced the Acd emission spectrum shown in red (F280 – F280,NoTAG). Ratio A values were calculated by dividing this spectrum by the hHv1-Y134Acd fluorescence spectrum obtained by direct excitation at 370 nm (F370). (E) Ratio A traces of the hHv1-Acd proteins colored according to (C). The ratio between the spectra of free Acd amino acid excited at 280 and 370 nm (Ratio A0) is shown as broken lines. (F) Mean Ratio A – Ratio A0 values (410–480 nm; N=4) as a function of the predicted FRET efficiencies from the AlphaFold hHv1 structural model, colored according to (C). The broken line is the best fit to the equation (Ratio A – Ratio A0) = m(Predicted FRET efficiency).
Figure 5. Spectral FRET analysis using Trp and Tyr donors and Acd as acceptor. (A) Fluorescence emission spectra of the intrinsic fluorescent amino acids Trp (black) and Tyr (black, broken lines), along with the Acd absorption spectrum in Buffer-H2 (blue). (B) AlphaFold dimer hHv1 structural model with the amino acids colored according to (C) and the native tryptophan and tyrosine residues shown as yellow spheres. (C) Normalized fluorescence spectra of the purified hHv1-Acd proteins (Excitation = 280 nm). The spectra were normalized by the Trp/Tyr fluorescence. The colors correspond to the indicated hHv1-Acd protein, and the remaining spectra are shown as grey traces in the figure. The No TAG sample (black) contains purified hHv1 protein without any amber stop codon expressed in the presence of Acd and the aminoacyl-tRNA synthetase/tRNA pair. (D) Example of the spectral FRET analysis procedure. The fluorescence spectrum of hHv1-Y134Acd obtained when exciting at 280 nm (black, F280) minus the normalized spectrum at the same excitation wavelength of the No TAG sample (grey, F280,NoTAG) produced the Acd emission spectrum shown in red (F280 – F280,NoTAG). Ratio A values were calculated by dividing this spectrum by the hHv1-Y134Acd fluorescence spectrum obtained by direct excitation at 370 nm (F370). (E) Ratio A traces of the hHv1-Acd proteins colored according to (C). The ratio between the spectra of free Acd amino acid excited at 280 and 370 nm (Ratio A0) is shown as broken lines. (F) Mean Ratio A – Ratio A0 values (410–480 nm; N=4) as a function of the predicted FRET efficiencies from the AlphaFold hHv1 structural model, colored according to (C). The broken line is the best fit to the equation (Ratio A – Ratio A0) = m(Predicted FRET efficiency).CC BY · PubMed Central
Figure 6. FRET between Trp/Tyr and Acd reports a conformational rearrangement in response to Zn2+. (A) Normalized fluorescence emission spectra of hHv1-K169Acd (Excitation = 280 nm) in Buffer-H2 in the absence of Zn2+ (black, Apo), in the presence of 1 mM Zn2+ (red), or in the presence of 1 mM Zn2+ and 2 mM EDTA (blue). Spectra were normalized by the maximum intensity of the Acd emission spectrum of the same sample excited at 370 nm. (B) Spectral FRET analysis of hHv1-K169Acd in Buffer-H2 in the absence of Zn2+ (black, Apo), in the presence of 1 mM Zn2+ (red), or in the presence of 1 mM Zn2+ and 2 mM EDTA (blue). (C) Spectral FRET analysis of the hHv1-Acd proteins in Buffer-H2 in the absence (black, Apo) or presence of 1 mM Zn2+ (red). N=4, ***p<0.005, **p<0.01.
Figure 6. FRET between Trp/Tyr and Acd reports a conformational rearrangement in response to Zn2+. (A) Normalized fluorescence emission spectra of hHv1-K169Acd (Excitation = 280 nm) in Buffer-H2 in the absence of Zn2+ (black, Apo), in the presence of 1 mM Zn2+ (red), or in the presence of 1 mM Zn2+ and 2 mM EDTA (blue). Spectra were normalized by the maximum intensity of the Acd emission spectrum of the same sample excited at 370 nm. (B) Spectral FRET analysis of hHv1-K169Acd in Buffer-H2 in the absence of Zn2+ (black, Apo), in the presence of 1 mM Zn2+ (red), or in the presence of 1 mM Zn2+ and 2 mM EDTA (blue). (C) Spectral FRET analysis of the hHv1-Acd proteins in Buffer-H2 in the absence (black, Apo) or presence of 1 mM Zn2+ (red). N=4, ***p<0.005, **p<0.01.CC BY · PubMed Central

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  1. J. R. Lakowicz , Ed., Principles of Fluorescence Spectroscopy (Springer US, 2006). · DOI · Paper page
  2. 10.1371/journal.pcbi.1010834 · DOI

Metadata

Authors
Carmona, E. M., Zagotta, W. N., & Gordon, S. E.
Affiliations
University of Washington (US)
Corresponding author
Gordon, Sharona E.
ORCID
Venue
eLife
Publisher
openRxiv
Published
2025-10-24
Volume
15
ISSN
2050-084X (ISSN-L)
DOI
10.1101/2025.10.23.684235
PMC
PMC12633253
OpenAlex
W4415532066
Cited by
0
References
49
FWCI
0.00
Type
journal article
Language
en
Open access
Licence
Locations
  • eLife (publishedVersion, cc-by)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion, cc-by)
  • PubMed (publishedVersion)
  • PubMed Central (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (submittedVersion, cc-by)
Funders
National Institutes of Health (R01EY037223, R35GM145225, R01EY010329, R35GM148137)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Ion channel regulation and function
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Biophysics › Advanced Fluorescence Microscopy Techniques
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Structure and Dynamics
Keywords
genetic code expansion, fluorescence resonance energy transfer, conformational change, zinc regulation, voltage-sensing domain, coiled-coil domain, detergent micelles

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