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Ruppelt D, Ackermann ELM, Robinson T, Steinem C. Assessing the mechanism of facilitated proton transport across GUVs trapped in a microfluidic device. Biophys J 2024:S0006-3495(24)00489-2. [PMID: 39066477 DOI: 10.1016/j.bpj.2024.07.030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2024] [Revised: 07/02/2024] [Accepted: 07/22/2024] [Indexed: 07/28/2024] Open
Abstract
Proton transport across lipid membranes is one of the most fundamental reactions that make up living organisms. In vitro, however, the study of proton transport reactions can be very challenging due to limitations imposed by proton concentrations, compartment size, and unstirred layers as well as buffer exchange and buffer capacity. In this study, we have developed a proton permeation assay based on the microfluidic trapping of giant vesicles enclosing the pH-sensitive dye pyranine to address some of these challenges. Time-resolved fluorescence imaging upon a rapid pH shift enabled us to investigate the facilitated H+ permeation mediated by either a channel or a carrier. Specifically, we compared the proton transport rates as a function of different proton gradients of the channel gramicidin D and the proton carrier carbonyl cyanide-m-chlorophenyl hydrazone. Our results demonstrate the efficacy of the assay in monitoring proton transport reactions and distinguishing between a channel-like and a carrier-like mechanism. This groundbreaking result enabled us to elucidate the enigmatic mode of the proton permeation mechanism of the recently discovered natural fibupeptide lugdunin.
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Affiliation(s)
- Dominik Ruppelt
- Institute of Organic and Biomolecular Chemistry, Georg-August Universität Göttingen, Göttingen, Germany
| | - Elena L M Ackermann
- Institute of Organic and Biomolecular Chemistry, Georg-August Universität Göttingen, Göttingen, Germany
| | - Tom Robinson
- Institute for Bioengineering, School of Engineering, University of Edinburgh, Edinburgh, United Kingdom
| | - Claudia Steinem
- Institute of Organic and Biomolecular Chemistry, Georg-August Universität Göttingen, Göttingen, Germany.
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Höler S, Degreif D, Stix F, Yang S, Gao S, Nagel G, Moroni A, Thiel G, Bertl A, Rauh O. Tailoring baker's yeast Saccharomyces cerevisiae for functional testing of channelrhodopsin. PLoS One 2023; 18:e0280711. [PMID: 37053213 PMCID: PMC10101416 DOI: 10.1371/journal.pone.0280711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Accepted: 03/28/2023] [Indexed: 04/14/2023] Open
Abstract
Channelrhodopsin 2 (ChR2) and its variants are the most frequent tools for remote manipulation of electrical properties in cells via light. Ongoing attempts try to enlarge their functional spectrum with respect to ion selectivity, light sensitivity and protein trafficking by mutations, protein engineering and environmental mining of ChR2 variants. A shortcoming in the required functional testing of large numbers of ChR2 variants is the lack of an easy screening system. Baker's yeast, which was successfully employed for testing ion channels from eukaryotes has not yet been used for screening of ChR2s, because they neither produce the retinal chromophore nor its precursor carotenoids. We found that addition of retinal to the external medium was not sufficient for detecting robust ChR activity in yeast in simple growth assays. This obstacle was overcome by metabolic engineering of a yeast strain, which constitutively produces retinal. In proof of concept experiments we functionally express different ChR variants in these cells and monitor their blue light induced activity in simple growth assays. We find that light activation of ChR augments an influx of Na+ with a consequent inhibition of cell growth. In a K+ uptake deficient yeast strain, growth can be rescued in selective medium by the blue light induced K+ conductance of ChR. This yeast strain can now be used as chassis for screening of new functional ChR variants and mutant libraries in simple yeast growth assays under defined selective conditions.
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Affiliation(s)
- Sebastian Höler
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Daniel Degreif
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Florentine Stix
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Shang Yang
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Shiqiang Gao
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Georg Nagel
- Institute of Physiology-Neurophysiology, Biocentre, Julius-Maximilians-University, Wuerzburg, Germany
| | - Anna Moroni
- Department of Biosciences and CNR IBF-Mi, Università degli Studi di Milano, Milano, Italy
| | - Gerhard Thiel
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Adam Bertl
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Oliver Rauh
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
- Centre for Synthetic Biology, Technische Universität Darmstadt, Darmstadt, Germany
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Islam MS, Gaston JP, Baker MAB. Fluorescence Approaches for Characterizing Ion Channels in Synthetic Bilayers. MEMBRANES 2021; 11:857. [PMID: 34832086 PMCID: PMC8619978 DOI: 10.3390/membranes11110857] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 10/25/2021] [Accepted: 10/28/2021] [Indexed: 12/12/2022]
Abstract
Ion channels are membrane proteins that play important roles in a wide range of fundamental cellular processes. Studying membrane proteins at a molecular level becomes challenging in complex cellular environments. Instead, many studies focus on the isolation and reconstitution of the membrane proteins into model lipid membranes. Such simpler, in vitro, systems offer the advantage of control over the membrane and protein composition and the lipid environment. Rhodopsin and rhodopsin-like ion channels are widely studied due to their light-interacting properties and are a natural candidate for investigation with fluorescence methods. Here we review techniques for synthesizing liposomes and for reconstituting membrane proteins into lipid bilayers. We then summarize fluorescence assays which can be used to verify the functionality of reconstituted membrane proteins in synthetic liposomes.
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Affiliation(s)
- Md. Sirajul Islam
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Kensington, NSW 2052, Australia; (M.S.I.); (J.P.G.)
| | - James P. Gaston
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Kensington, NSW 2052, Australia; (M.S.I.); (J.P.G.)
| | - Matthew A. B. Baker
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Kensington, NSW 2052, Australia; (M.S.I.); (J.P.G.)
- CSIRO Synthetic Biology Future Science Platform, GPO Box 2583, Brisbane, QLD 4001, Australia
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