1
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Liu TT, Huang SH, Chao L. Rapid Enrichment of a Native Multipass Transmembrane Protein via Cell Membrane Electrophoresis through Buffer pH and Ionic Strength Adjustment. J Am Chem Soc 2024; 146:11634-11647. [PMID: 38628144 PMCID: PMC11066866 DOI: 10.1021/jacs.3c13579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2023] [Revised: 04/02/2024] [Accepted: 04/02/2024] [Indexed: 05/02/2024]
Abstract
Supported membrane electrophoresis is a promising technique for collecting membrane proteins in native bilayer environments. However, the slow mobility of typical transmembrane proteins has impeded the technique's advancement. Here, we successfully applied cell membrane electrophoresis to rapidly enrich a 12-transmembrane helix protein, glucose transporter 1 with antibodies (GLUT1 complex), by tuning the buffer pH and ionic strength. The identified conditions allowed the separation of the GLUT1 complex and a lipid probe, Fast-DiO, within a native-like environment in a few minutes. A force model was developed to account for distinct electric and drag forces acting on the transmembrane and aqueous-exposed portion of a transmembrane protein as well as the electroosmotic force. This model not only elucidates the impact of size and charge properties of transmembrane proteins but also highlights the influence of pH and ionic strength on the driving forces and, consequently, electrophoretic mobility. Model predictions align well with experimentally measured electrophoretic mobilities of the GLUT1 complex and Fast-DiO at various pH and ionic strengths as well as with several lipid probes, lipid-anchored proteins, and reconstituted membrane proteins from previous studies. Force analyses revealed the substantial membrane drag of the GLUT1 complex, significantly slowing down electrophoretic mobility. Besides, the counterbalance of similar magnitudes of electroosmotic and electric forces results in a small net driving force and, consequently, reduced mobility under typical neutral pH conditions. Our results further highlight how the size and charge properties of transmembrane proteins influence the suitable range of operating conditions for effective movement, providing potential applications for concentrating and isolating membrane proteins within this platform.
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Affiliation(s)
- Tzu-Tzu Liu
- Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
| | - Sin-Han Huang
- Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
| | - Ling Chao
- Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
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2
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Pace HP, Hannestad JK, Armonious A, Adamo M, Agnarsson B, Gunnarsson A, Micciulla S, Sjövall P, Gerelli Y, Höök F. Structure and Composition of Native Membrane Derived Polymer-Supported Lipid Bilayers. Anal Chem 2018; 90:13065-13072. [PMID: 30350611 DOI: 10.1021/acs.analchem.8b04110] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Over the last two decades, supported lipid bilayers (SLBs) have been extensively used as model systems to study cell membrane structure and function. While SLBs have been traditionally produced from simple lipid mixtures, there has been a recent surge in compositional complexity to better mimic cellular membranes and thereby bridge the gap between classic biophysical approaches and cell experiments. To this end, native cellular membrane derived SLBs (nSLBs) have emerged as a new category of SLBs. As a new type of biomimetic material, an analytical workflow must be designed to characterize its molecular composition and structure. Herein, we demonstrate how a combination of fluorescence microscopy, neutron reflectometry, and secondary ion mass spectrometry offers new insights on structure, composition, and quality of nSLB systems formed using so-called hybrid vesicles, which are a mixture of native membrane material and synthetic lipids. With this approach, we demonstrate that the nSLB formed a continuous structure with complete mixing of the synthetic and native membrane components and a molecular stoichiometry that essentially mirrors that of the hybrid vesicles. Furthermore, structural investigation of the nSLB revealed that PEGylated lipids do not significantly thicken the hydration layer between the bilayer and substrate when on silicon substrates; however, nSLBs do have more topology than their simpler, purely synthetic counterparts. Beyond new insights regarding the structure and composition of nSLB systems, this work also serves to guide future researchers in producing and characterizing nSLBs from their cellular membrane of choice.
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Affiliation(s)
- Hudson P Pace
- Department of Physics , Chalmers University of Technology , SE-412 96 Göteborg , Sweden
| | - Jonas K Hannestad
- Department of Physics , Chalmers University of Technology , SE-412 96 Göteborg , Sweden.,Biosciences and Materials , Research Institutes of Sweden , SE-501 15 Borås , Sweden
| | - Antonious Armonious
- Department of Physics , Chalmers University of Technology , SE-412 96 Göteborg , Sweden
| | - Marco Adamo
- Institute Laue-Langevin , 38000 Grenoble , France.,Department of Chemical Engineering , Imperial College London , London SW7 2AZ , United Kingdom
| | - Bjorn Agnarsson
- Department of Physics , Chalmers University of Technology , SE-412 96 Göteborg , Sweden
| | - Anders Gunnarsson
- Discovery Sciences, IMED Biotech Unit , AstraZeneca , Gothenburg , Sweden
| | - Samantha Micciulla
- Institute Laue-Langevin , 38000 Grenoble , France.,Max Planck Institute of Colloids and Interfaces , 14476 Potsdam , Germany
| | - Peter Sjövall
- Department of Physics , Chalmers University of Technology , SE-412 96 Göteborg , Sweden.,Biosciences and Materials , Research Institutes of Sweden , SE-501 15 Borås , Sweden
| | - Yuri Gerelli
- Institute Laue-Langevin , 38000 Grenoble , France
| | - Fredrik Höök
- Department of Physics , Chalmers University of Technology , SE-412 96 Göteborg , Sweden
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3
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Shin D, Lee D, Kim Y, Kim I, Paek J, Kim J. Comparison of freeze vacuum drying and conventional drying methods in matrix-assisted laser desorption/ionization mass spectrometry analyses of peptides. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2018; 32:1746-1750. [PMID: 29971856 DOI: 10.1002/rcm.8225] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2018] [Revised: 06/23/2018] [Accepted: 06/25/2018] [Indexed: 06/08/2023]
Affiliation(s)
- Dongwon Shin
- Department of Chemistry, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Dabin Lee
- Department of Chemistry, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Yeoseon Kim
- Department of Chemistry, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Inyoung Kim
- Department of Chemistry, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Jihyun Paek
- Department of Chemistry, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Jeongkwon Kim
- Department of Chemistry, Chungnam National University, Daejeon, 34134, Republic of Korea
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4
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Harvey DJ. Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014. MASS SPECTROMETRY REVIEWS 2018; 37:353-491. [PMID: 29687922 DOI: 10.1002/mas.21530] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 11/29/2016] [Indexed: 06/08/2023]
Abstract
This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.
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Affiliation(s)
- David J Harvey
- Target Discovery Institute, Nuffield Department of Medicine, University of Oxford, Roosevelt Drive, Oxford, OX3 7FZ, United Kingdom
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5
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Bao P, Cartron ML, Sheikh KH, Johnson BRG, Hunter CN, Evans SD. Controlling transmembrane protein concentration and orientation in supported lipid bilayers. Chem Commun (Camb) 2018; 53:4250-4253. [PMID: 28361139 DOI: 10.1039/c7cc01023k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The trans-membrane protein - proteorhodopsin (pR) has been incorporated into supported lipid bilayers (SLB). In-plane electric fields have been used to manipulate the orientation and concentration of these proteins, within the SLB, through electrophoresis leading to a 25-fold increase concentration of pR.
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Affiliation(s)
- P Bao
- School of Physics & Astronomy, University of Leeds, LS2 9JT, UK.
| | - M L Cartron
- Department of Molecular Biology & Biotechnology, University of Sheffield, S10 2TH, UK
| | - K H Sheikh
- School of Biomedical Science, University of Leeds, LS2 9JT, UK
| | - B R G Johnson
- School of Physics & Astronomy, University of Leeds, LS2 9JT, UK.
| | - C N Hunter
- Department of Molecular Biology & Biotechnology, University of Sheffield, S10 2TH, UK
| | - S D Evans
- School of Physics & Astronomy, University of Leeds, LS2 9JT, UK.
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6
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Gao T, Wang B, Shi L, Zhu X, Xiang Y, Anzai JI, Li G. Ultrasensitive Quantitation of Plasma Membrane Proteins via isRTA. Anal Chem 2017; 89:10776-10782. [PMID: 28930447 DOI: 10.1021/acs.analchem.7b02025] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Quantitation of plasma membrane proteins (PMPs) is fundamental and frequently performed daily in the lab. However, challenged by the inherent/interacting heterostructures and complex surroundings of the PMPs in lipid membrane, quantitative techniques for PMP often require complex treatments (e.g., labeling, isolation, purification, and determination), and the sensitivity is usually not satisfactory. To address this problem, we have proposed a novel method that enables quantitation of PMPs with extremely high sensitivity, in an easier-to-manipulate and more streamlined way. This method is based on the design of an in situ rolling cycling replication-templated amplification strategy (isRTA). In fact, two rounds of DNA cascade isothermal amplifications have been conducted. The first round of amplification can provide templates for the second round of amplification; thus, significant enhancement of quantitative signals can be achieved. In this way, PMPs are quantified with ultrahigh sensitivity; as few as 25 copies of PMPs can be detected per cell. Moreover, the advantages of isRTA have been demonstrated by simultaneous identification of several PMP biomarkers (MUC1, EpCAM, and HER2) that are expressed over a wide distribution range on breast cancer cells. The precise typing of breast cancer cell subsets is thus possible because of the "quantitative-to-qualitative" strategy. Therefore, the unprecedented sensitivity and high usability of the isRTA method may present significant prospects for delving into membrane proteins and their related biofunctions in many research fields.
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Affiliation(s)
- Tao Gao
- State Key Laboratory of Pharmaceutical Biotechnology and Collaborative Innovation Center of Chemistry for Life Sciences, Department of Biochemistry, Nanjing University , Nanjing 210093, P. R. China
| | - Bei Wang
- State Key Laboratory of Pharmaceutical Biotechnology and Collaborative Innovation Center of Chemistry for Life Sciences, Department of Biochemistry, Nanjing University , Nanjing 210093, P. R. China
| | - Liu Shi
- State Key Laboratory of Pharmaceutical Biotechnology and Collaborative Innovation Center of Chemistry for Life Sciences, Department of Biochemistry, Nanjing University , Nanjing 210093, P. R. China
| | - Xiaoli Zhu
- Center for Molecular Recognition and Biosensing, School of Life Sciences, Shanghai University , Shanghai 200444, P. R. China
| | - Yang Xiang
- State Key Laboratory of Pharmaceutical Biotechnology and Collaborative Innovation Center of Chemistry for Life Sciences, Department of Biochemistry, Nanjing University , Nanjing 210093, P. R. China
| | - Jun-Ichi Anzai
- Graduate School of Pharmaceutical Sciences, Tohoku University , Aramaki, Aoba-ku, Sendai 980-8578, Japan
| | - Genxi Li
- State Key Laboratory of Pharmaceutical Biotechnology and Collaborative Innovation Center of Chemistry for Life Sciences, Department of Biochemistry, Nanjing University , Nanjing 210093, P. R. China.,Center for Molecular Recognition and Biosensing, School of Life Sciences, Shanghai University , Shanghai 200444, P. R. China
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7
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Lozano MM, Hovis JS, Moss FR, Boxer SG. Dynamic Reorganization and Correlation among Lipid Raft Components. J Am Chem Soc 2016; 138:9996-10001. [PMID: 27447959 DOI: 10.1021/jacs.6b05540] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Lipid rafts are widely believed to be an essential organizational motif in cell membranes. However, direct evidence for interactions among lipid and/or protein components believed to be associated with rafts is quite limited owing, in part, to the small size and intrinsically dynamic interactions that lead to raft formation. Here, we exploit the single negative charge on the monosialoganglioside GM1, commonly associated with rafts, to create a gradient of GM1 in response to an electric field applied parallel to a patterned supported lipid bilayer. The composition of this gradient is visualized by imaging mass spectrometry using a NanoSIMS. Using this analytical method, added cholesterol and sphingomyelin, both neutral and not themselves displaced by the electric field, are observed to reorganize with GM1. This dynamic reorganization provides direct evidence for an attractive interaction among these raft components into some sort of cluster. At steady state we obtain an estimate for the composition of this cluster.
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Affiliation(s)
- Mónica M Lozano
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
| | - Jennifer S Hovis
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
| | - Frank R Moss
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
| | - Steven G Boxer
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
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8
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van Weerd J, Karperien M, Jonkheijm P. Supported Lipid Bilayers for the Generation of Dynamic Cell-Material Interfaces. Adv Healthc Mater 2015; 4:2743-79. [PMID: 26573989 DOI: 10.1002/adhm.201500398] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 08/03/2015] [Indexed: 12/13/2022]
Abstract
Supported lipid bilayers (SLB) offer unique possibilities for studying cellular membranes and have been used as a synthetic architecture to interact with cells. Here, the state-of-the-art in SLB-based technology is presented. The fabrication, analysis, characteristics and modification of SLBs are described in great detail. Numerous strategies to form SLBs on different substrates, and the means to patteren them, are described. The use of SLBs as model membranes for the study of membrane organization and membrane processes in vitro is highlighted. In addition, the use of SLBs as a substratum for cell analysis is presented, with discrimination between cell-cell and cell-extracellular matrix (ECM) mimicry. The study is concluded with a discussion of the potential for in vivo applications of SLBs.
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Affiliation(s)
- Jasper van Weerd
- Bioinspired Molecular Engineering; University of Twente; PO Box 217 7500 AE Enschede The Netherlands
- Dept. of Developmental BioEngineering; MIRA Institute for Biomedical Technology and Technical Medicine; University of Twente; PO Box 217 7500 AE Enschede The Netherlands
- Molecular Nanofabrication Group, MESA+; University of Twente; Enschede 7500 AE The Netherlands
| | - Marcel Karperien
- Dept. of Developmental BioEngineering; MIRA Institute for Biomedical Technology and Technical Medicine; University of Twente; PO Box 217 7500 AE Enschede The Netherlands
| | - Pascal Jonkheijm
- Bioinspired Molecular Engineering; University of Twente; PO Box 217 7500 AE Enschede The Netherlands
- Molecular Nanofabrication Group, MESA+; University of Twente; Enschede 7500 AE The Netherlands
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9
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Pace H, Simonsson Nyström L, Gunnarsson A, Eck E, Monson C, Geschwindner S, Snijder A, Höök F. Preserved transmembrane protein mobility in polymer-supported lipid bilayers derived from cell membranes. Anal Chem 2015; 87:9194-203. [PMID: 26268463 DOI: 10.1021/acs.analchem.5b01449] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Supported lipid bilayers (SLBs) have contributed invaluable information about the physiochemical properties of cell membranes, but their compositional simplicity often limits the level of knowledge that can be gained about the structure and function of transmembrane proteins in their native environment. Herein, we demonstrate a generic protocol for producing polymer-supported lipid bilayers on glass surfaces that contain essentially all naturally occurring cell-membrane components of a cell line while still retaining transmembrane protein mobility and activity. This was achieved by merging vesicles made from synthetic lipids (PEGylated lipids and POPC lipids) with native cell-membrane vesicles to generate hybrid vesicles which readily rupture into a continuous polymer-supported lipid bilayer. To investigate the properties of these complex hybrid SLBs and particularly the behavior of their integral membrane-proteins, we used total internal reflection fluorescence imaging to study a transmembrane protease, β-secretase 1 (BACE1), whose ectoplasmic and cytoplasmic domains could both be specifically targeted with fluorescent reporters. By selectively probing the two different orientations of BACE1 in the resulting hybrid SLBs, the role of the PEG-cushion on transmembrane protein lateral mobility was investigated. The results reveal the necessity of having the PEGylated lipids present during vesicle adsorption to prevent immobilization of transmembrane proteins with protruding domains. The proteolytic activity of BACE1 was unadulterated by the sonication process used to merge the synthetic and native membrane vesicles; importantly it was also conserved in the SLB. The presented strategy could thus serve both fundamental studies of membrane biophysics and the production of surface-based bioanalytical sensor platforms.
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Affiliation(s)
- Hudson Pace
- Department of Applied Physics, Chalmers University of Technology , SE-41296 Gothenburg, Sweden
| | - Lisa Simonsson Nyström
- Department of Applied Physics, Chalmers University of Technology , SE-41296 Gothenburg, Sweden
| | - Anders Gunnarsson
- Discovery Sciences, AstraZeneca R&D Mölndal , SE-43183 Mölndal, Sweden
| | - Elizabeth Eck
- Department of Applied Physics, Chalmers University of Technology , SE-41296 Gothenburg, Sweden
| | - Christopher Monson
- Department of Physical Science, Southern Utah University , Cedar City, Utah 84720 United States
| | | | - Arjan Snijder
- Discovery Sciences, AstraZeneca R&D Mölndal , SE-43183 Mölndal, Sweden
| | - Fredrik Höök
- Department of Applied Physics, Chalmers University of Technology , SE-41296 Gothenburg, Sweden
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10
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Krabbenborg SO, van Weerd J, Karperien M, Jonkheijm P, Huskens J. Locked-in biomimetic surface gradients that are tunable in size, density and functionalization. Chemphyschem 2014; 15:3460-5. [PMID: 25115904 DOI: 10.1002/cphc.201402509] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Indexed: 11/09/2022]
Abstract
Tuneable and stable surface-chemical gradients in supported lipid bilayers (SLBs) hold great promise for a range of applications in biological sensing and screening. Yet, until now, no method has been reported that provides temporal control of SLB gradients. Herein we report on the development of locked-in SLB gradients that can be tuned in space, time and density by applying a process to control lipid phase behaviour, electric field and temperature. Stable gradients of charged Texas-Red-, serine- or biotin-terminated lipids have been prepared. For example, the Texas-Red surface density was varied from 0 to 2 mol %, while the length was varied between several tens to several hundreds of microns. At room temperature the gradients are shown to be stable up to 24 h, while at 60 °C the gradients could be erased in 30 min. Covalent and non-covalent chemical modification of the gradients is demonstrated, for example, by FITC, hexahistidine-tagged proteins, and SAv/biotin. The amenability to various (bio)chemistries paves the way for novel SLB-based gradients, useful in sensing, high-throughput screening and for understanding dynamic biological processes.
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Affiliation(s)
- Sven O Krabbenborg
- Molecular NanoFabrication Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede (The Netherlands)
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11
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van Weerd J, Krabbenborg SO, Eijkel J, Karperien M, Huskens J, Jonkheijm P. On-chip electrophoresis in supported lipid bilayer membranes achieved using low potentials. J Am Chem Soc 2014; 136:100-3. [PMID: 24345193 PMCID: PMC3901391 DOI: 10.1021/ja411287u] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Indexed: 01/10/2023]
Abstract
A micro supported lipid bilayer (SLB) electrophoresis method was developed, which functions at low potentials and appreciable operating times. To this end, (hydroxymethyl)-ferrocene (FcCH2OH) was employed to provide an electrochemical reaction at the anode and cathode at low applied potential to avoid electrolysis of water. The addition of FcCH2OH did not alter the SLB characteristics or affect biomolecule function, and pH and temperature variations and bubble formation were eliminated. Applying potentials of 0.25-1.2 V during flow gave homogeneous electrical fields and a fast, reversible, and strong build-up of a charged dye-modified lipid in the direction of the oppositely charged electrode. Moreover, streptavidin mobility could be modulated. This method paves the way for further development of analytical devices.
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Affiliation(s)
- Jasper van Weerd
- Molecular nanoFabrication group and BIOS lab-on-a-chip
group, MESA Institute for Nanotechnology, University
of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
- Developmental
Bioengineering, MIRA Biomedical Technology and Technical Medicine, University of Twente,
P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Sven O. Krabbenborg
- Molecular nanoFabrication group and BIOS lab-on-a-chip
group, MESA Institute for Nanotechnology, University
of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Jan Eijkel
- Molecular nanoFabrication group and BIOS lab-on-a-chip
group, MESA Institute for Nanotechnology, University
of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Marcel Karperien
- Developmental
Bioengineering, MIRA Biomedical Technology and Technical Medicine, University of Twente,
P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Jurriaan Huskens
- Molecular nanoFabrication group and BIOS lab-on-a-chip
group, MESA Institute for Nanotechnology, University
of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Pascal Jonkheijm
- Molecular nanoFabrication group and BIOS lab-on-a-chip
group, MESA Institute for Nanotechnology, University
of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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12
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Abstract
While electrophoresis in lipid bilayers has been performed since the 1970s, the technique has until now been unable to accurately measure the charge on lipids and proteins within the membrane based on drift velocity measurements. Part of the problem is caused by the use of the Einstein-Smoluchowski equation to estimate the electrophoretic mobility of such species. The source of the error arises from the fact that a lipid headgroup is typically smaller than the Debye length of the adjacent aqueous solution in most electrophoresis experiments. Instead, the Henry equation can more accurately predict the electrophoretic mobility at sufficient ionic strength. This was done for three dye-labeled lipids with different sized head groups and a charge on each lipid of -1. Also, the charge was measured as a function of pH for two titratable lipids that were fluorescently labeled. Finally, it was shown that the Henry equation also has difficulties measuring the correct lipid charge at salt concentrations below 5 mM, where electroosmotic forces are more significant.
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Affiliation(s)
- Matthew F Poyton
- Department of Chemistry, Department of Biochemistry and Molecular Biology, Penn State University , State College, Pennsylvania 16802, United States
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