1
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Roy B, Guha P, Chang CH, Nahak P, Karmakar G, Bykov AG, Akentiev AV, Noskov BA, Patra A, Dutta K, Ghosh C, Panda AK. Effect of cationic dendrimer on membrane mimetic systems in the form of monolayer and bilayer. Chem Phys Lipids 2024; 258:105364. [PMID: 38040405 DOI: 10.1016/j.chemphyslip.2023.105364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Revised: 10/01/2023] [Accepted: 11/26/2023] [Indexed: 12/03/2023]
Abstract
Interactions between a zwitterionic phospholipid, 1, 2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and four anionic phospholipids dihexadecyl phosphate (DHP), 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), 1, 2-dipalmitoyl-sn-glycero-3-phosphate (DPP) and 1, 2-dipalmitoyl-sn-glycero-3-phospho ethanol (DPPEth) in combination with an additional amount of 30 mol% cholesterol were separately investigated at air-buffer interface through surface pressure (π) - area (A) measurements. π-A isotherm derived parameters revealed maximum negative deviation from ideality for the mixtures comprising 30 mol% anionic lipids. Besides the film functionality, structural changes of the monomolecular films at different surface pressures in the absence and presence of polyamidoamine (PAMAM, generation 4), a cationic dendrimer, were visualised through Brewster angle microscopy and fluorescence microscopic studies. Fluidity/rigidity of monolayers were assessed by surface dilatational rheology studies. Effect of PAMAM on the formation of adsorbed monolayer, due to bilayer disintegration of liposomes (DPPC:anionic lipids= 7:3 M/M, and 30 mol% cholesterol) were monitored by surface pressure (π) - time (t) isotherms. Bilayer disintegration kinetics were dependent on lipid head group and chain length, besides dendrimer concentration. Such studies are considered to be an in vitro cell membrane model where the alteration of molecular orientation play important roles in understanding the nature of interaction between the dendrimer and cell membrane. Liposome-dendrimer aggregates were nontoxic to breast cancer cell line as well as in doxorubicin treated MDA-MB-468 cell line suggesting their potential as drug delivery systems.
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Affiliation(s)
- Biplab Roy
- Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India; Chemistry of Interfaces Group, Luleå University of Technology, SE-971 87 Luleå, Sweden
| | - Pritam Guha
- Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India; Department for Biomaterials Research, Polymer Institute, Slovak Academy of Sciences, 845 41 Bratislava, Slovakia
| | - Chien-Hsiang Chang
- Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan
| | - Prasant Nahak
- Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India
| | - Gourab Karmakar
- Department of Chemistry, University of North Bengal, Darjeeling 734 013, West Bengal, India
| | - Alexey G Bykov
- Department of Colloid Chemistry, St. Petersburg State University, Universitetsky pr. 26, 198504 St. Petersburg, Russia
| | - Alexander V Akentiev
- Department of Colloid Chemistry, St. Petersburg State University, Universitetsky pr. 26, 198504 St. Petersburg, Russia
| | - Boris A Noskov
- Department of Colloid Chemistry, St. Petersburg State University, Universitetsky pr. 26, 198504 St. Petersburg, Russia
| | - Anuttam Patra
- Chemistry of Interfaces Group, Luleå University of Technology, SE-971 87 Luleå, Sweden
| | - Kunal Dutta
- Department of Human Physiology, Vidyasagar University, Midnapore 721102, West Bengal, India
| | - Chandradipa Ghosh
- Department of Human Physiology, Vidyasagar University, Midnapore 721102, West Bengal, India
| | - Amiya Kumar Panda
- Department of Chemistry, Vidyasagar University, Midnapore 721102, West Bengal, India.
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2
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Islam MM, Nawagamuwage SU, Parshin IV, Richard MC, Burin AL, Rubtsov IV. Probing the Hydrophobic Region of a Lipid Bilayer at Specific Depths Using Vibrational Spectroscopy. J Am Chem Soc 2023; 145:26363-26373. [PMID: 37982703 DOI: 10.1021/jacs.3c10178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2023]
Abstract
A novel spectroscopic approach for studying the flexibility and mobility in the hydrophobic interior of lipid bilayers at specific depths is proposed. A set of test compounds featuring an azido moiety and a cyano or carboxylic acid moiety, connected by an alkyl chain of different lengths, was synthesized. FTIR data and molecular dynamics calculations indicated that the test compounds in a bilayer are oriented so that the cyano or carboxylic acid moiety is located in the lipid head-group region, while the azido group stays inside the bilayer at the depth determined by its alkyl chain length. We found that the asymmetric stretching mode of the azido group (νN3) can serve as a reporter of the membrane interior dynamics. FTIR and two-dimensional infrared (2DIR) studies were performed at different temperatures, ranging from 22 to 45 °C, covering the Lβ-Lα phase transition temperature of dipalmitoylphosphatidylcholine (∼41 °C). The width of the νN3 peak was found to be very sensitive to the phase transition and to the temperature in general. We introduced an order parameter, SN3, which characterizes restrictions to motion inside the bilayer. 2DIR spectra of νN3 showed different extents of inhomogeneity at different depths in the bilayer, with the smallest inhomogeneity in the middle of the leaflet. The spectral diffusion dynamics of the N3 peak was found to be dependent on the depth of the N3 group location in the bilayer. The obtained results enhance our understanding of the bilayer dynamics and can be extended to investigate membranes with more complex compositions.
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Affiliation(s)
- Md Muhaiminul Islam
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | | | - Igor V Parshin
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Margaret C Richard
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Alexander L Burin
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Igor V Rubtsov
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
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3
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Go YJ, Kalathingal M, Rhee YM. Elucidating activation and deactivation dynamics of VEGFR-2 transmembrane domain with coarse-grained molecular dynamics simulations. PLoS One 2023; 18:e0281781. [PMID: 36795710 PMCID: PMC9934429 DOI: 10.1371/journal.pone.0281781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 02/01/2023] [Indexed: 02/17/2023] Open
Abstract
The vascular endothelial growth factor receptor 2 (VEGFR-2) is a member of receptor tyrosine kinases (RTKs) and is a dimeric membrane protein that functions as a primary regulator of angiogenesis. As is usual with RTKs, spatial alignment of its transmembrane domain (TMD) is essential toward VEGFR-2 activation. Experimentally, the helix rotations within TMD around their own helical axes are known to participate importantly toward the activation process in VEGFR-2, but the detailed dynamics of the interconversion between the active and inactive TMD forms have not been clearly elucidated at the molecular level. Here, we attempt to elucidate the process by using coarse grained (CG) molecular dynamics (MD) simulations. We observe that inactive dimeric TMD in separation is structurally stable over tens of microseconds, suggesting that TMD itself is passive and does not allow spontaneous signaling of VEGFR-2. By starting from the active conformation, we reveal the mechanism of TMD inactivation through analyzing the CG MD trajectories. We observe that interconversions between a left-handed overlay and a right-handed one are essential for the process of going from an active TMD structure to the inactive form. In addition, our simulations find that the helices can rotate properly when the overlaying structure of the helices interconverts and when the crossing angle of the two helices changes by larger than ~40 degrees. As the activation right after the ligand attachment on VEGFR-2 will take place in the reverse manner of this inactivation process, these structural aspects will also appear importantly for the activation process. The rather large change in helix configuration for activation also explains why VEGFR-2 rarely self-activate and how the activating ligand structurally drive the whole VEGFR-2. This mechanism of TMD activation / inactivation within VEGFR-2 may help in further understanding the overall activation processes of other RTKs.
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Affiliation(s)
- Yeon Ju Go
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea
| | - Mahroof Kalathingal
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Korea
| | - Young Min Rhee
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea
- * E-mail:
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4
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van Aalst EJ, Borcik CG, Wylie BJ. Spectroscopic signatures of bilayer ordering in native biological membranes. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183891. [PMID: 35217001 PMCID: PMC10793244 DOI: 10.1016/j.bbamem.2022.183891] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 02/08/2022] [Accepted: 02/09/2022] [Indexed: 06/14/2023]
Abstract
Membrane proteins and polycyclic lipids like cholesterol and hopanoids coordinate phospholipid bilayer ordering. This phenomenon manifests as partitioning of the liquid crystalline phase into liquid-ordered (Lo) and liquid-disordered (Ld) regions. In Eukaryotes, microdomains are rich in cholesterol and sphingolipids and serve as signal transduction scaffolds. In Prokaryotes, Lo microdomains increase pathogenicity and antimicrobial resistance. Previously, we identified spectroscopically distinct chemical shift signatures for all-trans (AT) and trans-gauche (TG) acyl chain conformations, cyclopropyl ring lipids (CPR), and hopanoids in prokaryotic lipid extracts and used Polarization Transfer (PT) SSNMR to investigate bilayer ordering. To investigate how these findings relate to native bilayer organization, we interrogate whole cell and whole membrane extract samples of Burkholderia thailendensis to investigate bilayer ordering in situ. In 13C-13C 2D SSNMR spectra, we assigned chemical shifts for lipid species in both samples, showing conservation of lipids of interest in our native membrane sample. A one-dimensional temperature series of PT SSNMR and transverse relaxation measurements of AT versus TG acyl conformations in the membrane sample confirm bilayer ordering and a broadened phase transition centered at a lower-than-expected temperature. Bulk protein backbone Cα dynamics and correlations consistent with lipid-protein contacts within are further indicative of microdomain formation and lipid ordering. In aggregate, these findings provide evidence for microdomain formation in vivo and provide insight into phase separation and transition mechanics in biological membranes.
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Affiliation(s)
- Evan J van Aalst
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79415, USA
| | - Collin G Borcik
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79415, USA
| | - Benjamin J Wylie
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79415, USA.
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5
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Klaiss-Luna MC, Manrique-Moreno M. Infrared Spectroscopic Study of Multi-Component Lipid Systems: A Closer Approximation to Biological Membrane Fluidity. MEMBRANES 2022; 12:534. [PMID: 35629860 PMCID: PMC9147058 DOI: 10.3390/membranes12050534] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/09/2022] [Revised: 05/05/2022] [Accepted: 05/16/2022] [Indexed: 01/10/2023]
Abstract
Membranes are essential to cellular organisms, and play several roles in cellular protection as well as in the control and transport of nutrients. One of the most critical membrane properties is fluidity, which has been extensively studied, using mainly single component systems. In this study, we used Fourier transform infrared spectroscopy to evaluate the thermal behavior of multi-component supported lipid bilayers that mimic the membrane composition of tumoral and non-tumoral cell membranes, as well as microorganisms such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus. The results showed that, for tumoral and non-tumoral membrane models, the presence of cholesterol induced a loss of cooperativity of the transition. However, in the absence of cholesterol, the transitions of the multi-component lipid systems had sigmoidal curves where the gel and fluid phases are evident and where main transition temperatures were possible to determine. Additionally, the possibility of designing multi-component lipid systems showed the potential to obtain several microorganism models, including changes in the cardiolipin content associated with the resistance mechanism in Staphylococcus aureus. Finally, the potential use of multi-component lipid systems in the determination of the conformational change of the antimicrobial peptide LL-37 was studied. The results showed that LL-37 underwent a conformational change when interacting with Staphylococcus aureus models, instead of with the erythrocyte membrane model. The results showed the versatile applications of multi-component lipid systems studied by Fourier transform infrared spectroscopy.
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Affiliation(s)
| | - Marcela Manrique-Moreno
- Chemistry Institute, Faculty of Exact and Natural Sciences, University of Antioquia, A.A. 1226, Medellin 050010, Colombia;
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6
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Pozza A, Giraud F, Cece Q, Casiraghi M, Point E, Damian M, Le Bon C, Moncoq K, Banères JL, Lescop E, Catoire LJ. Exploration of the dynamic interplay between lipids and membrane proteins by hydrostatic pressure. Nat Commun 2022; 13:1780. [PMID: 35365643 PMCID: PMC8975810 DOI: 10.1038/s41467-022-29410-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 03/14/2022] [Indexed: 02/06/2023] Open
Abstract
Cell membranes represent a complex and variable medium in time and space of lipids and proteins. Their physico-chemical properties are determined by lipid components which can in turn influence the biological function of membranes. Here, we used hydrostatic pressure to study the close dynamic relationships between lipids and membrane proteins. Experiments on the β–barrel OmpX and the α–helical BLT2 G Protein-Coupled Receptor in nanodiscs of different lipid compositions reveal conformational landscapes intimately linked to pressure and lipids. Pressure can modify the conformational landscape of the membrane protein per se, but also increases the gelation of lipids, both being monitored simultaneously at high atomic resolution by NMR. Our study also clearly shows that a membrane protein can modulate, at least locally, the fluidity of the bilayer. The strategy proposed herein opens new perspectives to scrutinize the dynamic interplay between membrane proteins and their surrounding lipids. Direct information on the dynamic interplay between membrane proteins and lipids is scarce. Here the authors report a detailed description of these close relationships by combining lipid nanodiscs and high-pressure NMR. They report the link between pressure and lipid compositions to the conformational landscape of the β-barrel OmpX and the α-helical BLT2 G Protein-Coupled Receptor in nanodiscs.
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Affiliation(s)
- Alexandre Pozza
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, UMR 7099, CNRS/Université de Paris, Institut de Biologie Physico-Chimique (IBPC, FRC 550), 75005, Paris, France
| | - François Giraud
- Institut de Chimie des Substances Naturelles (ICSN), CNRS UPR 2301, Université Paris-Saclay, 91198, Gif-sur-Yvette, France
| | - Quentin Cece
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, UMR 7099, CNRS/Université de Paris, Institut de Biologie Physico-Chimique (IBPC, FRC 550), 75005, Paris, France.,Laboratoire Cibles Thérapeutiques et Conception de Médicaments (CiTCoM), UMR 8038, CNRS/Université de Paris, Faculté de Pharmacie, 75270, Paris, Cedex 06, France
| | - Marina Casiraghi
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, UMR 7099, CNRS/Université de Paris, Institut de Biologie Physico-Chimique (IBPC, FRC 550), 75005, Paris, France.,Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 94305, Stanford, CA, USA
| | - Elodie Point
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, UMR 7099, CNRS/Université de Paris, Institut de Biologie Physico-Chimique (IBPC, FRC 550), 75005, Paris, France
| | - Marjorie Damian
- Institut des Biomolécules Max Mousseron (IBMM), Université de Montpellier, CNRS, ENSCM, Pôle Chimie Balard Recherche, 34293, Montpellier, cedex 5, France
| | - Christel Le Bon
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, UMR 7099, CNRS/Université de Paris, Institut de Biologie Physico-Chimique (IBPC, FRC 550), 75005, Paris, France
| | - Karine Moncoq
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, UMR 7099, CNRS/Université de Paris, Institut de Biologie Physico-Chimique (IBPC, FRC 550), 75005, Paris, France
| | - Jean-Louis Banères
- Institut des Biomolécules Max Mousseron (IBMM), Université de Montpellier, CNRS, ENSCM, Pôle Chimie Balard Recherche, 34293, Montpellier, cedex 5, France
| | - Ewen Lescop
- Institut de Chimie des Substances Naturelles (ICSN), CNRS UPR 2301, Université Paris-Saclay, 91198, Gif-sur-Yvette, France.
| | - Laurent J Catoire
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, UMR 7099, CNRS/Université de Paris, Institut de Biologie Physico-Chimique (IBPC, FRC 550), 75005, Paris, France.
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7
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Li H, Gao J, Cao L, Xie X, Fan J, Wang H, Wang H, Nie Z. A DNA Molecular Robot that Autonomously Walks on the Cell Membrane to Drive Cell Motility. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202108210] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Hao Li
- State Key Laboratory of Chemo/Biosensing and Chemometrics College of Chemistry and Chemical Engineering College of Biology Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology Hunan University Changsha 410082 P. R. China
- School of Pharmaceutical Sciences (Shenzhen) Sun Yat-sen University Shenzhen 518107 P. R. China
| | - Jing Gao
- State Key Laboratory of Electroanalytical Chemistry Research Center of Biomembranomics Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun 130022 Jilin P. R. China
| | - Lei Cao
- State Key Laboratory of Chemo/Biosensing and Chemometrics College of Chemistry and Chemical Engineering College of Biology Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology Hunan University Changsha 410082 P. R. China
| | - Xuan Xie
- State Key Laboratory of Chemo/Biosensing and Chemometrics College of Chemistry and Chemical Engineering College of Biology Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology Hunan University Changsha 410082 P. R. China
| | - Jiahui Fan
- State Key Laboratory of Chemo/Biosensing and Chemometrics College of Chemistry and Chemical Engineering College of Biology Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology Hunan University Changsha 410082 P. R. China
| | - Hongda Wang
- State Key Laboratory of Electroanalytical Chemistry Research Center of Biomembranomics Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun 130022 Jilin P. R. China
| | - Hong‐Hui Wang
- State Key Laboratory of Chemo/Biosensing and Chemometrics College of Chemistry and Chemical Engineering College of Biology Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology Hunan University Changsha 410082 P. R. China
| | - Zhou Nie
- State Key Laboratory of Chemo/Biosensing and Chemometrics College of Chemistry and Chemical Engineering College of Biology Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology Hunan University Changsha 410082 P. R. China
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8
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Abstract
Membrane proteins (MPs) play essential roles in numerous cellular processes. Because around 70% of the currently marketed drugs target MPs, a detailed understanding of their structure, binding properties, and functional dynamics in a physiologically relevant environment is crucial for a more detailed understanding of this important protein class. We here summarize the benefits of using lipid nanodiscs for NMR structural investigations and provide a detailed overview of the currently used lipid nanodisc systems as well as their applications in solution-state NMR. Despite the increasing use of other structural methods for the structure determination of MPs in lipid nanodiscs, solution NMR turns out to be a versatile tool to probe a wide range of MP features, ranging from the structure determination of small to medium-sized MPs to probing ligand and partner protein binding as well as functionally relevant dynamical signatures in a lipid nanodisc setting. We will expand on these topics by discussing recent NMR studies with lipid nanodiscs and work out a key workflow for optimizing the nanodisc incorporation of an MP for subsequent NMR investigations. With this, we hope to provide a comprehensive background to enable an informed assessment of the applicability of lipid nanodiscs for NMR studies of a particular MP of interest.
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Affiliation(s)
- Umut Günsel
- Bavarian NMR Center (BNMRZ) at the Department of Chemistry, Technical University of Munich, Ernst-Otto-Fischer-Strasse 2, 85748 Garching, Germany
| | - Franz Hagn
- Bavarian NMR Center (BNMRZ) at the Department of Chemistry, Technical University of Munich, Ernst-Otto-Fischer-Strasse 2, 85748 Garching, Germany.,Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany
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9
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Li H, Gao J, Cao L, Xie X, Fan J, Wang H, Wang HH, Nie Z. A DNA Molecular Robot that Autonomously Walks on the Cell Membrane to Drive Cell Motility. Angew Chem Int Ed Engl 2021; 60:26087-26095. [PMID: 34490693 DOI: 10.1002/anie.202108210] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Revised: 08/17/2021] [Indexed: 11/09/2022]
Abstract
Synthetic molecular robots can execute sophisticated molecular tasks at nanometer resolution. However, a molecular robot capable of controlling cellular behavior remains unexplored. Herein, we report a self-propelled DNA robot operating on the cell membrane to control the migration of a cell. Driven by DNAzyme catalytic activity, the DNA robot could autonomously and stepwise move on the membrane-floating cell-surface receptors in a stochastic manner and simultaneously trigger the receptor-dimerization to activate downstream signaling for cell motility. The cell membrane-associated continuous motion and operation of a DNA robot allowed for the ultrasensitive regulation of MET/AKT signaling and cytoskeleton remodeling to enhance cell migration. Finally, we designed distinct conditional DNA robots to orthogonally manipulate the cell migration in a coculture of mixed cell populations. We have developed a novel strategy to engineer a cell-driving molecular robot, representing a promising avenue for precise cell manipulation with nanoscale resolution.
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Affiliation(s)
- Hao Li
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, College of Biology, Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology, Hunan University, Changsha, 410082, P. R. China.,School of Pharmaceutical Sciences (Shenzhen), Sun Yat-sen University, Shenzhen, 518107, P. R. China
| | - Jing Gao
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, Jilin, P. R. China
| | - Lei Cao
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, College of Biology, Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology, Hunan University, Changsha, 410082, P. R. China
| | - Xuan Xie
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, College of Biology, Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology, Hunan University, Changsha, 410082, P. R. China
| | - Jiahui Fan
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, College of Biology, Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology, Hunan University, Changsha, 410082, P. R. China
| | - Hongda Wang
- State Key Laboratory of Electroanalytical Chemistry, Research Center of Biomembranomics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, Jilin, P. R. China
| | - Hong-Hui Wang
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, College of Biology, Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology, Hunan University, Changsha, 410082, P. R. China
| | - Zhou Nie
- State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, College of Biology, Hunan Provincial Key Laboratory of Biomacromolecular Chemical Biology, Hunan University, Changsha, 410082, P. R. China
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10
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Price JR, Afrose F, Greathouse DV, Koeppe RE. Illuminating Disorder Induced by Glu in a Stable Arg-Anchored Transmembrane Helix. ACS OMEGA 2021; 6:20611-20618. [PMID: 34396006 PMCID: PMC8359125 DOI: 10.1021/acsomega.1c02800] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 07/13/2021] [Indexed: 06/13/2023]
Abstract
Membrane proteins are vital for biological function and are complex to study. Even in model peptide-lipid systems, the combined influence or interaction of pairs of chemical groups still is not well understood. Disordered proteins, whether in solution or near lipid membranes, are an emerging paradigm for the initiation and control of biological function. The disorder can involve molecular orientation as well as molecular folding. This paper reports an astonishing induction of disorder when one Glu residue is introduced into a highly stable 23-residue transmembrane helix. The parent helix is anchored by a single Arg residue, tilted at a well-defined angle with respect to the DOPC bilayer normal and undergoes rapid cone precession. When Glu is introduced two residues away from Arg, with 200° (or 160°) radial separation, the helix properties change radically to exhibit a multiplicity of three or more disordered states. The helix characteristics have been monitored by deuterium (2H) NMR spectroscopy as functions of the pH and lipid bilayer composition. The disordered multistate behavior of the (Glu, Arg)-containing helix varies with the lipid bilayer thickness and pH. The results highlight a fundamental induction of protein multistate properties by a single Glu residue in a lipid membrane environment.
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11
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Fake It 'Till You Make It-The Pursuit of Suitable Membrane Mimetics for Membrane Protein Biophysics. Int J Mol Sci 2020; 22:ijms22010050. [PMID: 33374526 PMCID: PMC7793082 DOI: 10.3390/ijms22010050] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Revised: 12/17/2020] [Accepted: 12/19/2020] [Indexed: 12/13/2022] Open
Abstract
Membrane proteins evolved to reside in the hydrophobic lipid bilayers of cellular membranes. Therefore, membrane proteins bridge the different aqueous compartments separated by the membrane, and furthermore, dynamically interact with their surrounding lipid environment. The latter not only stabilizes membrane proteins, but directly impacts their folding, structure and function. In order to be characterized with biophysical and structural biological methods, membrane proteins are typically extracted and subsequently purified from their native lipid environment. This approach requires that lipid membranes are replaced by suitable surrogates, which ideally closely mimic the native bilayer, in order to maintain the membrane proteins structural and functional integrity. In this review, we survey the currently available membrane mimetic environments ranging from detergent micelles to bicelles, nanodiscs, lipidic-cubic phase (LCP), liposomes, and polymersomes. We discuss their respective advantages and disadvantages as well as their suitability for downstream biophysical and structural characterization. Finally, we take a look at ongoing methodological developments, which aim for direct in-situ characterization of membrane proteins within native membranes instead of relying on membrane mimetics.
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12
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Bibow S, Böhm R, Modaresi SM, Hiller S. Detergent Titration as an Efficient Method for NMR Resonance Assignments of Membrane Proteins in Lipid–Bilayer Nanodiscs. Anal Chem 2020; 92:7786-7793. [DOI: 10.1021/acs.analchem.0c00917] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Stefan Bibow
- Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
| | - Raphael Böhm
- Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
| | | | - Sebastian Hiller
- Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
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Fruehwirth S, Zehentner S, Salim M, Sterneder S, Tiroch J, Lieder B, Zehl M, Somoza V, Pignitter M. In Vitro Digestion of Grape Seed Oil Inhibits Phospholipid-Regulating Effects of Oxidized Lipids. Biomolecules 2020; 10:biom10050708. [PMID: 32370178 PMCID: PMC7277833 DOI: 10.3390/biom10050708] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 04/27/2020] [Accepted: 04/30/2020] [Indexed: 12/18/2022] Open
Abstract
The intake of dietary lipids is known to affect the composition of phospholipids in gastrointestinal cells, thereby influencing passive lipid absorption. However, dietary lipids rich in polyunsaturated fatty acids, such as vegetable oils, are prone to oxidation. Studies investigating the phospholipid-regulating effect of oxidized lipids are lacking. We aimed at identifying the effects of oxidized lipids from moderately (18.8 ± 0.39 meq O2/kg oil) and highly (28.2 ± 0.39 meq O2/kg oil) oxidized and in vitro digested cold-pressed grape seed oils on phospholipids in human gastric tumor cells (HGT-1). The oils were analyzed for their antioxidant constituents as well as their oxidized triacylglycerol profile by LC-MS/MS before and after a simulated digestion. The HGT-1 cells were treated with polar oil fractions containing epoxidized and hydroperoxidized triacylglycerols for up to six hours. Oxidized triacylglycerols from grape seed oil were shown to decrease during the in vitro digestion up to 40% in moderately and highly oxidized oil. The incubation of HGT-1 cells with oxidized lipids from non-digested oils induced the formation of cellular phospholipids consisting of unsaturated fatty acids, such as phosphocholines PC (18:1/22:6), PC (18:2/0:0), phosphoserine PS (42:8) and phosphoinositol PI (20:4/0:0), by about 40%–60%, whereas the incubation with the in vitro digested oils did not affect the phospholipid metabolism. Hence, the gastric conditions inhibited the phospholipid-regulating effect of oxidized triacylglycerols (oxTAGs), with potential implications in lipid absorption.
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Affiliation(s)
- Sarah Fruehwirth
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
| | - Sofie Zehentner
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
| | - Mohammed Salim
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
| | - Sonja Sterneder
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
| | - Johanna Tiroch
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
| | - Barbara Lieder
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
| | - Martin Zehl
- Department of Analytical Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria;
| | - Veronika Somoza
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
| | - Marc Pignitter
- Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, 1090 Vienna, Austria; (S.F.); (S.Z.); (M.S.); (S.S.); (J.T.); (B.L.); (V.S.)
- Correspondence: ; Tel.: +43-14277-70621
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14
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Xie CZ, Chang SM, Mamontov E, Stingaciu LR, Chen YF. Uncoupling between the lipid membrane dynamics of differing hierarchical levels. Phys Rev E 2020; 101:012416. [PMID: 32069643 DOI: 10.1103/physreve.101.012416] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Indexed: 11/07/2022]
Abstract
Diverse biological functions of biomembranes are made possible by their rich dynamic behaviors across multiple scales. While the potential coupling between the dynamics of differing scales may underlie the machineries regulating the biomembrane-involving processes, the mechanism and even the existence of this coupling remain an open question, despite the latter being taken for granted. Via inelastic neutron scattering, we examined dynamics across multiple scales for the lipid membranes whose dynamic behaviors were perturbed by configurational changes at two membrane regions. Surprisingly, the dynamic behavior of individual lipid molecules and their collective motions were not always coupled. This suggests that the expected causal relation between the dynamics of the differing hierarchical levels does not exist and that an apparent coupling can emerge by manipulating certain membrane configurations. The findings provide insight on biomembrane modeling and how cells might individually or concertedly control the multiscale membrane dynamics to regulate their functions.
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Affiliation(s)
- Cheng-Zhi Xie
- Department of Chemical and Materials Engineering, National Central University, Taoyuan 32001, Taiwan
| | - Shih-Min Chang
- Department of Chemical and Materials Engineering, National Central University, Taoyuan 32001, Taiwan
| | - Eugene Mamontov
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Laura R Stingaciu
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Yi-Fan Chen
- Department of Chemical and Materials Engineering, National Central University, Taoyuan 32001, Taiwan
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15
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Zhu K, Su H. Unraveling Dynamic Transitions in Time-Resolved Biomolecular Motions by A Dressed Diffusion Model. J Phys Chem A 2020; 124:613-617. [PMID: 31589443 DOI: 10.1021/acs.jpca.9b08142] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recent experimental data reveal the complexity of diffusion dynamics beyond the scope of classical Brownian dynamics. The particles exhibit diverse diffusive motions from the anomalous toward classical diffusion over a wide range of temporal scales. Here a dressed diffusion model is developed to account for non-Brownian phenomena. By coupling the particle dynamics with a local field, the dressed diffusion model generalizes the Langevin equation through coupled damping kernels and generates the salient feature of time-dependent diffusion dynamics reported in the experimental measurements of biomolecules. The dressed diffusion model provides one quantitative aspect for future endeavors in this rapid-growing field.
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Affiliation(s)
- Kaicheng Zhu
- Department of Chemistry , The Hong Kong University of Science and Technology , Clear Water Bay, Kowloon , Hong Kong
| | - Haibin Su
- Department of Chemistry , The Hong Kong University of Science and Technology , Clear Water Bay, Kowloon , Hong Kong
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16
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Bibow S. Exploring Lipid and Membrane Protein Dynamics Using Lipid-Bilayer Nanodiscs and Solution-State NMR Spectroscopy. Methods Mol Biol 2020; 2127:397-419. [PMID: 32112335 DOI: 10.1007/978-1-0716-0373-4_25] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The relationship of membrane protein function and the surrounding lipid bilayer goes far beyond simple hydrophobic interactions. At least from the 1980s, it is speculated that a certain fluid lipid state may be important not only for the lateral diffusion of membrane proteins (MPs) but also for modulating the catalytic activity of MPs (Lenaz. Bioscience Rep 7 (11):823-837, 1987). Indeed, acyl chain length, hydrophobic mismatch, and lipid headgroups are determinants for enzymatic and transport activities of MPs (Dumas et al. Biochemistry 39(16):4846-4854, 2000; Johannsson et al. Biochim Biophys Acta 641(2):416-421, 1981; Montecucco et al. FEBS Lett 144(1):145-148, 1982; Martens et al. Nat Struct Mol Biol 23(8):744-751, 2016). Moreover, it is speculated that changes in membrane lipid dynamics are important in the field of thermosensation (Vriens J, Nilius B, Voets T, Nat Rev Neurosci 15:573-589, 2014). Atomic insights into lipid-mediated modulation of membrane protein dynamics would therefore provide new insights with the potential to fundamentally extend our understanding on dynamic lipid-protein interdependencies.This chapter describes the expression and purification of nanodiscs assembled from membrane scaffold protein (MSP) as well as the expression and purification of the outer membrane protein X (OmpX). Subsequently, the incorporation of OmpX into MSP-derived nanodiscs is explained in detail. The chapter concludes with the setup of nuclear magnetic resonance (NMR) relaxation experiments and the extraction of relaxation rates for OmpX and the surrounding lipids.
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Affiliation(s)
- Stefan Bibow
- Biozentrum, University of Basel, Basel, Switzerland.
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17
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Peng X, Wen ZB, Yang P, Chai YQ, Liang WB, Yuan R. Biomimetic 3D DNA Nanomachine via Free DNA Walker Movement on Lipid Bilayers Supported by Hard SiO 2@CdTe Nanoparticles for Ultrasensitive MicroRNA Detection. Anal Chem 2019; 91:14920-14926. [PMID: 31674756 DOI: 10.1021/acs.analchem.9b03263] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Herein, a novel three-dimensional (3D) DNA nanomachine with high walking efficiency via free DNA walker movement on biomimetic lipid bilayers supported by hard silica@CdTe quantum dots (SiO2@CdTe) was constructed for ultrasensitive fluorescence detection of microRNA. The synthesized SiO2@CdTe nanoparticles were adopted as the fluorescence indicator and spherical carrier of lipid bilayers, and then the DNA substrates were anchored on lipid bilayers with biomimetic fluidity through the cholesterol-lipid interaction. Once target microRNA-141 interacted with the 3D DNA nanomachine to release cholesterol labeled arm (Chol-arm), the Chol-arm could generate a series of strand displacement reactions by moving freely on the lipid bilayers, resulting in the releasement of numerous quenchers from the SiO2@CdTe nanoparticles and inducing a strong fluorescence signal. Impressively, compared with traditional 3D DNA nanomachine conjugating DNA substrates on hard surfaces (such as gold or silica) with limited reactivity, the proposed biomimetic 3D DNA nanomachine not only immobilized DNA substrates rapidly and effectively but also kept it with a favorable fluidity, which significantly enhanced the walking efficiency. As expected, the biomimetic 3D DNA nanomachine for fluorescence detection of microRNA-141 exhibited an excellent performance with a detection limit of 0.21 pM and presented promising properties in cell lysate detection and intracellular imaging. Thus, the described biomimetic 3D DNA nanomachine provided a novel avenue for sensitive detection of biomolecules, which could be useful for bioanalysis and early clinical diagnoses of disease.
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Affiliation(s)
- Xin Peng
- Key Laboratory of Luminescent and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering , Southwest University , Chongqing 400715 , P.R. China
| | - Zhi-Bin Wen
- Key Laboratory of Luminescent and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering , Southwest University , Chongqing 400715 , P.R. China
| | - Peng Yang
- Key Laboratory of Luminescent and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering , Southwest University , Chongqing 400715 , P.R. China
| | - Ya-Qin Chai
- Key Laboratory of Luminescent and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering , Southwest University , Chongqing 400715 , P.R. China
| | - Wen-Bin Liang
- Key Laboratory of Luminescent and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering , Southwest University , Chongqing 400715 , P.R. China
| | - Ruo Yuan
- Key Laboratory of Luminescent and Real-Time Analytical Chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering , Southwest University , Chongqing 400715 , P.R. China
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18
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Bibow S. Opportunities and Challenges of Backbone, Sidechain, and RDC Experiments to Study Membrane Protein Dynamics in a Detergent-Free Lipid Environment Using Solution State NMR. Front Mol Biosci 2019; 6:103. [PMID: 31709261 PMCID: PMC6823230 DOI: 10.3389/fmolb.2019.00103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 09/19/2019] [Indexed: 12/22/2022] Open
Abstract
Whereas solution state NMR provided a wealth of information on the dynamics landscape of soluble proteins, only few studies have investigated membrane protein dynamics in a detergent-free lipid environment. Recent developments of smaller nanodiscs and other lipid-scaffolding polymers, such as styrene maleic acid (SMA), however, open new and promising avenues to explore the function-dynamics relationship of membrane proteins as well as between membrane proteins and their surrounding lipid environment. Favorably sized lipid-bilayer nanodiscs, established membrane protein reconstitution protocols and sophisticated solution NMR relaxation methods probing dynamics over a wide range of timescales will eventually reveal unprecedented lipid-membrane protein interdependencies that allow us to explain things we have not been able to explain so far. In particular, methyl group dynamics resulting from CEST, CPMG, ZZ exchange, and RDC experiments are expected to provide new and surprising insights due to their proximity to lipids, their applicability in large 100+ kDa assemblies and their simple labeling due to the availability of commercial precursors. This review summarizes the recent developments of membrane protein dynamics with a special focus on membrane protein dynamics in lipid-bilayer nanodiscs. Opportunities and challenges of backbone, side chain and RDC dynamics applied to membrane proteins are discussed. Solution-state NMR and lipid nanodiscs bear great potential to change our molecular understanding of lipid-membrane protein interactions.
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Affiliation(s)
- Stefan Bibow
- Biozentrum, University of Basel, Basel, Switzerland
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Lipinski K, McKay MJ, Afrose F, Martfeld AN, Koeppe RE, Greathouse DV. Influence of Lipid Saturation, Hydrophobic Length and Cholesterol on Double-Arginine-Containing Helical Peptides in Bilayer Membranes. Chembiochem 2019; 20:2784-2792. [PMID: 31150136 DOI: 10.1002/cbic.201900282] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Indexed: 12/12/2022]
Abstract
Membrane proteins are essential for many cell processes yet are more difficult to investigate than soluble proteins. Charged residues often contribute significantly to membrane protein function. Model peptides such as GWALP23 (acetyl-GGALW5 LAL8 LALALAL16 ALW19 LAGA-amide) can be used to characterize the influence of specific residues on transmembrane protein domains. We have substituted R8 and R16 in GWALP23 in place of L8 and L16, equidistant from the peptide center, and incorporated specific 2 H-labeled alanine residues within the central sequence for detection by solid-state 2 H NMR spectroscopy. The resulting pattern of [2 H]Ala quadrupolar splitting (Δνq ) magnitudes indicates the core helix for R8,16 GWALP23 is significantly tilted to give a similar transmembrane orientation in thinner bilayers with either saturated C12:0 or C14:0 acyl chains (1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)) or unsaturated C16:1 Δ9 cis acyl chains. In bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC; C18:1 Δ9 cis) multiple orientations are indicated, whereas in longer, unsaturated 1,2-dieicosenoyl-sn-glycero-3-phosphocholine (DEiPC; C20:1 Δ11 cis) bilayers, the R8,16 GWALP23 helix adopts primarily a surface orientation. The inclusion of 10-20 mol % cholesterol in DOPC bilayers drives more of the R8,16 GWALP23 helix population to the membrane surface, thereby allowing both charged arginines access to the interfacial lipid head groups. The results suggest that hydrophobic thickness and cholesterol content are more important than lipid saturation for the arginine peptide dynamics and helix orientation in lipid membranes.
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Affiliation(s)
- Karli Lipinski
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Matthew J McKay
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Fahmida Afrose
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Ashley N Martfeld
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA.,Present address: Department Department of Neurobiology, Duke University Medical Center, 311 Research Drive, Durham, NC, 27710, USA
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
| | - Denise V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, 119 Chemistry Building, Fayetteville, AR, 72701, USA
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