1
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Banerjee P, Monje-Galvan V, Voth GA. Cooperative Membrane Binding of HIV-1 Matrix Proteins. J Phys Chem B 2024; 128:2595-2606. [PMID: 38477117 PMCID: PMC10962350 DOI: 10.1021/acs.jpcb.3c06222] [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: 09/15/2023] [Revised: 02/24/2024] [Accepted: 02/27/2024] [Indexed: 03/14/2024]
Abstract
The HIV-1 assembly process begins with a newly synthesized Gag polyprotein being targeted to the inner leaflet of the plasma membrane of the infected cells to form immature viral particles. Gag-membrane interactions are mediated through the myristoylated (Myr) N-terminal matrix (MA) domain of Gag, which eventually multimerize on the membrane to form trimers and higher order oligomers. The study of the structure and dynamics of peripheral membrane proteins like MA has been challenging for both experimental and computational studies due to the complex transient dynamics of protein-membrane interactions. Although the roles of anionic phospholipids (PIP2, PS) and the Myr group in the membrane targeting and stable membrane binding of MA are now well-established, the cooperative interactions between the MA monomers and MA-membrane remain elusive in the context of viral assembly and release. Our present study focuses on the membrane binding dynamics of a higher order oligomeric structure of MA protein (a dimer of trimers), which has not been explored before. Employing time-lagged independent component analysis (tICA) to our microsecond-long trajectories, we investigate conformational changes of the matrix protein induced by membrane binding. Interestingly, the Myr switch of an MA monomer correlates with the conformational switch of adjacent monomers in the same trimer. Together, our findings suggest complex protein dynamics during the formation of the immature HIV-1 lattice; while MA trimerization facilitates Myr insertion, MA trimer-trimer interactions in the immature lattice can hinder the same.
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Affiliation(s)
- Puja Banerjee
- Department of Chemistry,
Chicago Center for Theoretical Chemistry, Institute for Biophysical
Dynamics, and James Franck Institute, The
University of Chicago, Chicago, Illinois 60637, United States
| | | | - Gregory A. Voth
- Department of Chemistry,
Chicago Center for Theoretical Chemistry, Institute for Biophysical
Dynamics, and James Franck Institute, The
University of Chicago, Chicago, Illinois 60637, United States
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2
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Rostovtseva TK, Weinrich M, Jacobs D, Rosencrans WM, Bezrukov SM. Dimeric Tubulin Modifies Mechanical Properties of Lipid Bilayer, as Probed Using Gramicidin A Channel. Int J Mol Sci 2024; 25:2204. [PMID: 38396879 PMCID: PMC10889239 DOI: 10.3390/ijms25042204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 01/31/2024] [Accepted: 02/05/2024] [Indexed: 02/25/2024] Open
Abstract
Using the gramicidin A channel as a molecular probe, we show that tubulin binding to planar lipid membranes changes the channel kinetics-seen as an increase in the lifetime of the channel dimer-and thus points towards modification of the membrane's mechanical properties. The effect is more pronounced in the presence of non-lamellar lipids in the lipid mixture used for membrane formation. To interpret these findings, we propose that tubulin binding redistributes the lateral pressure of lipid packing along the membrane depth, making it closer to the profile expected for lamellar lipids. This redistribution happens because tubulin perturbs the lipid headgroup spacing to reach the membrane's hydrophobic core via its amphiphilic α-helical domain. Specifically, it increases the forces of repulsion between the lipid headgroups and reduces such forces in the hydrophobic region. We suggest that the effect is reciprocal, meaning that alterations in lipid bilayer mechanics caused by membrane remodeling during cell proliferation in disease and development may also modulate tubulin membrane binding, thus exerting regulatory functions. One of those functions includes the regulation of protein-protein interactions at the membrane surface, as exemplified by VDAC complexation with tubulin.
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Affiliation(s)
- Tatiana K. Rostovtseva
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
| | - Michael Weinrich
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Daniel Jacobs
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
| | - William M. Rosencrans
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
- Department of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Sergey M. Bezrukov
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA (S.M.B.)
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3
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Banerjee P, Qu K, Briggs JAG, Voth GA. Molecular dynamics simulations of HIV-1 matrix-membrane interactions at different stages of viral maturation. Biophys J 2024; 123:389-406. [PMID: 38196190 PMCID: PMC10870173 DOI: 10.1016/j.bpj.2024.01.006] [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: 09/25/2023] [Revised: 12/05/2023] [Accepted: 01/04/2024] [Indexed: 01/11/2024] Open
Abstract
Although the structural rearrangement of the membrane-bound matrix (MA) protein trimers upon HIV-1 maturation has been reported, the consequences of MA maturation on the MA-lipid interactions are not well understood. Long-timescale molecular dynamics simulations of the MA multimeric assemblies of immature and mature virus particles with our realistic asymmetric membrane model have explored MA-lipid interactions and lateral organization of lipids around MA complexes. The number of stable MA-phosphatidylserine and MA-phosphatidylinositol 4,5-bisphosphate (PIP2) interactions at the trimeric interface of the mature MA complex is observed to be greater compared to that of the immature MA complex. Our simulations identified an alternative PIP2-binding site in the immature MA complex where the multivalent headgroup of a PIP2 lipid with a greater negative charge binds to multiple basic amino acid residues such as ARG3 residues of both the MA monomers at the trimeric interface and highly basic region (HBR) residues (LYS29, LYS31) of one of the MA monomers. Our enhanced sampling simulations have explored the conformational space of phospholipids at different binding sites of the trimer-trimer interface of MA complexes that are not accessible by conventional unbiased molecular dynamics. Unlike the immature MA complex, the 2' acyl tail of two PIP2 lipids at the trimeric interface of the mature MA complex is observed to sample stable binding pockets of MA consisting of helix-4 residues. Together, our results provide molecular-level insights into the interactions of MA trimeric complexes with membrane and different lipid conformations at the specific binding sites of MA protein before and after viral maturation.
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Affiliation(s)
- Puja Banerjee
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, The University of Chicago, Chicago, Illinois
| | - Kun Qu
- Infectious Diseases Translational Research Programme, Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - John A G Briggs
- Department of Cell and Virus Structure, Max Planck Institute of Biochemistry, Planegg, Germany
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, The University of Chicago, Chicago, Illinois.
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4
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Pham P, Hilty C. Biomolecular interactions studied by low-field NMR using SABRE hyperpolarization. Chem Sci 2023; 14:10258-10263. [PMID: 37772094 PMCID: PMC10530938 DOI: 10.1039/d3sc02365f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Accepted: 08/31/2023] [Indexed: 09/30/2023] Open
Abstract
We demonstrate that low-field nuclear magnetic resonance provides a means for measuring biomacromolecular interactions without requiring a superconducting, or even a permanent magnet. A small molecule, 5-fluoropyridine-3-carboximidamide, is designed to be a specific ligand for the trypsin protein, while containing a fluorine atom as a nuclear spin hyperpolarizable label. With hyperpolarization by the parahydrogen based signal amplification by the reversible exchange method, fluorine NMR signals are detectable in the measurement field of 0.85 mT of an electromagnet, at a concentration of less than 100 μM. As a weak ligand for the protein, the hyperpolarized molecule can serve as a reporter for measuring the binding of other ligands of interest, illustrated by the determination of the dissociation constant KD of benzamidine from changes in the observed R2 relaxation rates. A signal enhancement of more than 106 compared to Boltzmann polarization at the measurement field indicates that this experiment is not feasible without prepolarization. The extended magnetic field range for the measurement of biomolecular interactions under near physiological conditions, with a protein concentration on the order of 10 μM or less, provides a new option for screening of ligand binding, measurement of protein-protein interactions, and measurement of molecular dynamics.
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Affiliation(s)
- Pierce Pham
- Department of Chemistry, Texas A&M University 3255 TAMU College Station TX 77843 USA
| | - Christian Hilty
- Department of Chemistry, Texas A&M University 3255 TAMU College Station TX 77843 USA
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5
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Banerjee P, Monje-Galvan V, Voth GA. Cooperative Membrane Binding of HIV-1 Matrix Proteins. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.22.559012. [PMID: 37790356 PMCID: PMC10542177 DOI: 10.1101/2023.09.22.559012] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
The HIV-1 assembly process begins with a newly synthesized Gag polyprotein being targeted to the inner leaflet of the plasma membrane of the infected cells to form immature viral particles. Gag-membrane interactions are mediated through the myristoylated(Myr) N-terminal matrix (MA) domain of Gag which eventually multimerize on the membrane to form trimers and higher-order oligomers. The study of the structure and dynamics of peripheral membrane proteins like MA has been challenging for both experimental and computational studies due to the complex dynamics of protein-membrane interactions. Although the roles of anionic phospholipids (PIP2, PS) and the Myr group in the membrane targeting and stable membrane binding of MA are now well-established, the cooperative interactions between MA monomers and MA-membrane still remain elusive. Our present study focuses on the membrane binding dynamics of a higher-order oligomeric structure of MA protein (a dimer of trimers), which has not been explored before. Employing time-lagged independent component analysis (tICA) to our microsecond-long trajectories, we investigate conformational changes of the matrix protein induced by membrane binding. Interestingly, the Myr switch of a MA monomer correlates with the conformational switch of adjacent monomers in the same trimer. Together, our findings suggest that MA trimerization facilitates Myr insertion, but MA trimer-trimer interactions in the lattice of immature HIV-1 particles can hinder the same. Additionally, local lipid density patterns of different lipid species provide a signature of the initial stage of lipid-domain formation upon membrane binding of the protein complex. TOC
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6
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Eddehech A, Rahier R, Donnarumma D, Rigano F, Noiriel A, Abousalham A, Cacciola F, Mondello L, Zarai Z. Development of a highly efficient oil degumming process using a novel phosphatidylinositol-specific phospholipase C enzyme from Bacillus thuringiensis PL14. FOOD BIOSCI 2023. [DOI: 10.1016/j.fbio.2023.102579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
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7
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Moutoussamy E, Khan HM, Roberts MF, Gershenson A, Chipot C, Reuter N. Standard Binding Free Energy and Membrane Desorption Mechanism for a Phospholipase C. J Chem Inf Model 2022; 62:6602-6613. [PMID: 35343689 PMCID: PMC9795555 DOI: 10.1021/acs.jcim.1c01543] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Peripheral membrane proteins (PMPs) bind temporarily to cellular membranes and play important roles in signaling, lipid metabolism, and membrane trafficking. Obtaining accurate membrane-PMP affinities using experimental techniques is more challenging than for protein-ligand affinities in an aqueous solution. At the theoretical level, calculation of the standard protein-membrane binding free energy using molecular dynamics simulations remains a daunting challenge owing to the size of the biological objects at play, the slow lipid diffusion, and the large variation in configurational entropy that accompanies the binding process. To overcome these challenges, we used a computational framework relying on a series of potential-of-mean-force (PMF) calculations including a set of geometrical restraints on collective variables. This methodology allowed us to determine the standard binding free energy of a PMP to a phospholipid bilayer using an all-atom force field. Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (BtPI-PLC) was chosen due to its importance as a virulence factor and owing to the host of experimental affinity data available. We computed a standard binding free energy of -8.2 ± 1.4 kcal/mol in reasonable agreement with the reported experimental values (-6.6 ± 0.2 kcal/mol). In light of the 2.3-μs separation PMF calculation, we investigated the mechanism whereby BtPI-PLC disengages from interactions with the lipid bilayer during separation. We describe how a short amphipathic helix engages in transitory interactions to ease the passage of its hydrophobes through the interfacial region upon desorption from the bilayer.
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Affiliation(s)
- Emmanuel
E. Moutoussamy
- Department
of Biological Sciences, University of Bergen, N-5020 Bergen, Norway,Computational
Biology Unit, Department of Informatics, University of Bergen, N-5020 Bergen, Norway
| | - Hanif M. Khan
- Department
of Biological Sciences, University of Bergen, N-5020 Bergen, Norway,Computational
Biology Unit, Department of Informatics, University of Bergen, N-5020 Bergen, Norway
| | - Mary F. Roberts
- Department
of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | - Anne Gershenson
- Department
of Biochemistry and Molecular Biology, University
of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
| | - Christophe Chipot
- Laboratoire
International Associé Centre National de la Recherche Scientifique
et University of Illinois at Urbana−Champaign, Unité
Mixte de Recherche n 7019, Université
de Lorraine, BP 70239, 54506 Vandœuvre-lès-Nancy cedex, France,Department
of Physics, University of Illinois, Urbana, Illinois 61801, United States
| | - Nathalie Reuter
- Computational
Biology Unit, Department of Informatics, University of Bergen, N-5020 Bergen, Norway,Department
of Chemistry, University of Bergen, N-5020 Bergen, Norway,
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8
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Roberts MF, Gershenson A, Reuter N. Phosphatidylcholine Cation—Tyrosine π Complexes: Motifs for Membrane Binding by a Bacterial Phospholipase C. Molecules 2022; 27:molecules27196184. [PMID: 36234717 PMCID: PMC9572076 DOI: 10.3390/molecules27196184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2022] [Revised: 09/14/2022] [Accepted: 09/15/2022] [Indexed: 10/27/2022] Open
Abstract
Phosphatidylinositol-specific phospholipase C (PI-PLC) enzymes are a virulence factor in many Gram-positive organisms. The specific activity of the Bacillus thuringiensis PI-PLC is significantly increased by adding phosphatidylcholine (PC) to vesicles composed of the substrate phosphatidylinositol, in part because the inclusion of PC reduces the apparent Kd for the vesicle binding by as much as 1000-fold when comparing PC-rich vesicles to PI vesicles. This review summarizes (i) the experimental work that localized a site on BtPI-PLC where PC is bound as a PC choline cation—Tyr-π complex and (ii) the computational work (including all-atom molecular dynamics simulations) that refined the original complex and found a second persistent PC cation—Tyr-π complex. Both complexes are critical for vesicle binding. These results have led to a model for PC functioning as an allosteric effector of the enzyme by altering the protein dynamics and stabilizing an ‘open’ active site conformation.
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Affiliation(s)
- Mary F. Roberts
- Department of Chemistry, Boston College, Chestnut Hill, MA 02467, USA
- Correspondence: ; Tel.: +1-617-460-5194
| | - Anne Gershenson
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - Nathalie Reuter
- Computational Biology Unit, Department of Informatics and Chemistry, University of Bergen, 5020 Bergen, Norway
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9
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Roberts MF, Hedstrom L. High Resolution 31P Field Cycling NMR Reveals Unsuspected Features of Enzyme-Substrate-Cofactor Dynamics. Front Mol Biosci 2022; 9:865519. [PMID: 35433832 PMCID: PMC9009223 DOI: 10.3389/fmolb.2022.865519] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Accepted: 03/16/2022] [Indexed: 11/13/2022] Open
Abstract
The dynamic interactions of enzymes and substrates underpins catalysis, yet few techniques can interrogate the dynamics of protein-bound ligands. Here we describe the use of field cycling NMR relaxometry to measure the dynamics of enzyme-bound substrates and cofactors in catalytically competent complexes of GMP reductase. These studies reveal new binding modes unanticipated by x-ray crystal structures and reaction-specific dynamic networks. Importantly, this work demonstrates that distal interactions not usually considered part of the reaction coordinate can play an active role in catalysis. The commercialization of shuttling apparatus will make field cycling relaxometry more accessible and expand its use to additional nuclei, promising more intriguing findings to come.
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Affiliation(s)
- Mary F. Roberts
- Department of Chemistry, Boston College, Chestnut Hill, MA, United States
| | - Lizbeth Hedstrom
- Departments of Biology and Chemistry, Brandeis University, Waltham, MA, United States
- *Correspondence: Lizbeth Hedstrom,
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10
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Roberts MF, Cai J, V Natarajan S, Khan HM, Reuter N, Gershenson A, Redfield AG. Phospholipids in Motion: High-Resolution 31P NMR Field Cycling Studies. J Phys Chem B 2021; 125:8827-8838. [PMID: 34320805 DOI: 10.1021/acs.jpcb.1c02105] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Diverse phospholipid motions are key to membrane function but can be quite difficult to untangle and quantify. High-resolution field cycling 31P NMR spin-lattice relaxometry, where the sample is excited at high field, shuttled in the magnet bore for low-field relaxation, then shuttled back to high field for readout of the residual magnetization, provides data on phospholipid dynamics and structure. This information is encoded in the field dependence of the 31P spin-lattice relaxation rate (R1). In the field range from 11.74 down to 0.003 T, three dipolar nuclear magnetic relaxation dispersions (NMRDs) and one due to 31P chemical shift anisotropy contribute to R1 of phospholipids. Extraction of correlation times and maximum relaxation amplitudes for these NMRDs provides (1) lateral diffusion constants for different phospholipids in the same bilayer, (2) estimates of how additives alter the motion of the phospholipid about its long axis, and (3) an average 31P-1H angle with respect to the bilayer normal, which reveals that polar headgroup motion is not restricted on a microsecond timescale. Relative motions within a phospholipid are also provided by comparing 31P NMRD profiles for specifically deuterated molecules as well as 13C and 1H field dependence profiles to that of 31P. Although this work has dealt exclusively with phospholipids in small unilamellar vesicles, these same NMRDs can be measured for phospholipids in micelles and nanodisks, making this technique useful for monitoring lipid behavior in a variety of structures and assessing how additives alter specific lipid motions.
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Affiliation(s)
- Mary F Roberts
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | - Jingfei Cai
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | - Sivanandam V Natarajan
- Department of Biochemistry and the Rosenstiel Basic Medical Sciences Research Institute, Brandeis University, Waltham, Massachusetts 02454, United States
| | - Hanif M Khan
- Department of Molecular Biology and Computational Biology Unit, Department of Informatics, University of Bergen, 5020 Bergen, Norway
| | - Nathalie Reuter
- Department of Molecular Biology and Computational Biology Unit, Department of Informatics, University of Bergen, 5020 Bergen, Norway
| | - Anne Gershenson
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003, United States
| | - Alfred G Redfield
- Department of Biochemistry and the Rosenstiel Basic Medical Sciences Research Institute, Brandeis University, Waltham, Massachusetts 02454, United States
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11
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Pemberton JG, Kim YJ, Humpolickova J, Eisenreichova A, Sengupta N, Toth DJ, Boura E, Balla T. Defining the subcellular distribution and metabolic channeling of phosphatidylinositol. J Cell Biol 2020; 219:133809. [PMID: 32211894 PMCID: PMC7054996 DOI: 10.1083/jcb.201906130] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 11/08/2019] [Accepted: 12/23/2019] [Indexed: 02/06/2023] Open
Abstract
Phosphatidylinositol (PI) is an essential structural component of eukaryotic membranes that also serves as the common precursor for polyphosphoinositide (PPIn) lipids. Despite the recognized importance of PPIn species for signal transduction and membrane homeostasis, there is still a limited understanding of the relationship between PI availability and the turnover of subcellular PPIn pools. To address these shortcomings, we established a molecular toolbox for investigations of PI distribution within intact cells by exploiting the properties of a bacterial enzyme, PI-specific PLC (PI-PLC). Using these tools, we find a minor presence of PI in membranes of the ER, as well as a general enrichment within the cytosolic leaflets of the Golgi complex, peroxisomes, and outer mitochondrial membrane, but only detect very low steady-state levels of PI within the plasma membrane (PM) and endosomes. Kinetic studies also demonstrate the requirement for sustained PI supply from the ER for the maintenance of monophosphorylated PPIn species within the PM, Golgi complex, and endosomal compartments.
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Affiliation(s)
- Joshua G Pemberton
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Yeun Ju Kim
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Jana Humpolickova
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Prague, Czech Republic
| | - Andrea Eisenreichova
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Prague, Czech Republic
| | - Nivedita Sengupta
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Daniel J Toth
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Evzen Boura
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Prague, Czech Republic
| | - Tamas Balla
- Section on Molecular Signal Transduction, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
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12
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Tao K, Waletich JR, Arredondo F, Tyler BM. Manipulating Endoplasmic Reticulum-Plasma Membrane Tethering in Plants Through Fluorescent Protein Complementation. FRONTIERS IN PLANT SCIENCE 2019; 10:635. [PMID: 31191568 PMCID: PMC6547045 DOI: 10.3389/fpls.2019.00635] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Accepted: 04/26/2019] [Indexed: 05/21/2023]
Abstract
The bimolecular fluorescence complementation (BiFC) assay has been widely used to examine interactions between integral and peripheral proteins within putative plasma membrane (PM) microdomains. In the course of using BiFC assays to examine the co-localization of plasma membrane (PM) targeted receptor-like kinases (RLKs), such as FLS2, with PM micro-domain proteins such as remorins, we unexpectedly observed heterogeneous distribution patterns of fluorescence on the PM of Nicotiana benthamiana leaf cortical cells. These patterns appeared to co-localize with the endoplasmic reticulum (ER) and with ER-PM contact sites, and closely resembled patterns caused by over-expression of the ER-PM tether protein Synaptotagmin1 (SYT1). Using domain swap experiments with SYT1, we inferred that non-specific dimerization between FLS2-VenusN and VenusC-StRem1.3 could create artificial ER-PM tether proteins analogous to SYT1. The same patterns of ER-PM tethering were produced when a representative set of integral membrane proteins were partnered in BiFC complexes with PM-targeted peripheral membrane proteins, including PtdIns(4)P-binding proteins. We inferred that spontaneous formation of mature fluorescent proteins caused the BiFC complexes to trap the integral membrane proteins in the ER during delivery to the PM, producing a PM-ER tether. This phenomenon could be a useful tool to deliberately manipulate ER-PM tethering or to test protein membrane localization. However, this study also highlights the risk of using the BiFC assay to study membrane protein interactions in plants, due to the possibility of alterations in cellular structures and membrane organization, or misinterpretation of protein-protein interactions. A number of published studies using this approach may therefore need to be revisited.
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Affiliation(s)
- Kai Tao
- Molecular and Cellular Biology Program, Oregon State University, Corvallis, OR, United States
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States
| | - Justin R. Waletich
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States
| | - Felipe Arredondo
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States
| | - Brett M. Tyler
- Molecular and Cellular Biology Program, Oregon State University, Corvallis, OR, United States
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States
- Center for Genome Research and Biocomputing, Oregon State University, Corvallis, OR, United States
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13
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Noack LC, Pejchar P, Sekereš J, Jaillais Y, Potocký M. Transient Gene Expression as a Tool to Monitor and Manipulate the Levels of Acidic Phospholipids in Plant Cells. Methods Mol Biol 2019; 1992:189-199. [PMID: 31148039 DOI: 10.1007/978-1-4939-9469-4_12] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Anionic phospholipids represent only minor fraction of cell membranes lipids but they are critically important for many membrane-related processes, including membrane identity, charge, shape, the generation of second messengers, and the recruitment of peripheral proteins. The main anionic phospholipids of the plasma membrane are phosphoinositides phosphatidylinositol 4-phosphate (PI4P), phosphatidylinositol 4,5-bisphosphate (PI4,5P2), phosphatidylserine (PS), and phosphatidic acid (PA). Recent insights in the understanding of the nature of protein-phospholipid interactions enabled the design of genetically encoded fluorescent molecular probes that can interact with various phospholipids in a specific manner allowing their imaging in live cells. Here, we describe the use of transiently transformed plant cells to study phospholipid-dependent membrane recruitment.
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Affiliation(s)
- Lise C Noack
- Laboratoire Reproduction et Développement des Plantes, Université de Lyon, ENS de Lyon, CNRS, INRA, Lyon, France
| | - Přemysl Pejchar
- Institute of Experimental Botany, Czech Academy of Sciences, Prague, Czech Republic
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Juraj Sekereš
- Institute of Experimental Botany, Czech Academy of Sciences, Prague, Czech Republic
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Yvon Jaillais
- Laboratoire Reproduction et Développement des Plantes, Université de Lyon, ENS de Lyon, CNRS, INRA, Lyon, France
| | - Martin Potocký
- Institute of Experimental Botany, Czech Academy of Sciences, Prague, Czech Republic.
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Prague, Czech Republic.
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14
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Roberts MF, Khan HM, Goldstein R, Reuter N, Gershenson A. Search and Subvert: Minimalist Bacterial Phosphatidylinositol-Specific Phospholipase C Enzymes. Chem Rev 2018; 118:8435-8473. [DOI: 10.1021/acs.chemrev.8b00208] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Mary F. Roberts
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | | | - Rebecca Goldstein
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | | | - Anne Gershenson
- Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
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15
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Rosenberg MM, Redfield AG, Roberts MF, Hedstrom L. Dynamic Characteristics of Guanosine-5'-monophosphate Reductase Complexes Revealed by High-Resolution 31P Field-Cycling NMR Relaxometry. Biochemistry 2018; 57:3146-3154. [PMID: 29547266 DOI: 10.1021/acs.biochem.8b00142] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ability of enzymes to modulate the dynamics of bound substrates and cofactors is a critical feature of catalysis, but the role of dynamics has largely been approached from the perspective of the protein. Here, we use an underappreciated NMR technique, subtesla high-resolution field-cycling 31P NMR relaxometry, to interrogate the dynamics of enzyme bound substrates and cofactors in guanosine-5'-monophosphate reductase (GMPR). These experiments reveal distinct binding modes and dynamic profiles associated with the 31P nuclei in the Michaelis complexes for the deamination and hydride transfer steps of the catalytic cycle. Importantly, the substrate is constrained and the cofactor is more dynamic in the deamination complex E·GMP·NADP+, whereas the substrate is more dynamic and the cofactor is constrained in the hydride transfer complex E·IMP·NADP+. The presence of D2O perturbed the relaxation of the 31P nuclei in E·IMP·NADP+ but not in E·GMP·NADP+, providing further evidence of distinct binding modes with different dynamic properties. dIMP and dGMP are poor substrates, and the dynamics of the cofactor complexes of dGMP/dIMP are disregulated relative to GMP/IMP. The substrate 2'-OH interacts with Asp219, and mutation of Asp219 to Ala decreases the value of Vmax by a factor of 30. Counterintuitively, loss of Asp219 makes both substrates and cofactors less dynamic. These observations suggest that the interactions between the substrate 2'-OH and Asp219 coordinate the dynamic properties of the Michaelis complexes, and these dynamics are important for progression through the catalytic cycle.
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Affiliation(s)
- Masha M Rosenberg
- Department of Biology , Brandeis University , MS009, 415 South Street , Waltham , Massachusetts 02453-9110 , United States
| | - Alfred G Redfield
- Department of Biochemistry , Brandeis University , MS009, 415 South Street , Waltham , Massachusetts 02453-9110 , United States
| | - Mary F Roberts
- Department of Chemistry , Boston College , 140 Commonwealth Avenue , Chestnut Hill , Massachusetts 02467-9110 , United States
| | - Lizbeth Hedstrom
- Department of Biology , Brandeis University , MS009, 415 South Street , Waltham , Massachusetts 02453-9110 , United States.,Department of Chemistry , Brandeis University , 415 South Street , Waltham , Massachusetts 02453-3808 , United States
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16
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Hoogerheide DP, Noskov SY, Jacobs D, Bergdoll L, Silin V, Worcester DL, Abramson J, Nanda H, Rostovtseva TK, Bezrukov SM. Structural features and lipid binding domain of tubulin on biomimetic mitochondrial membranes. Proc Natl Acad Sci U S A 2017; 114:E3622-E3631. [PMID: 28420794 PMCID: PMC5422764 DOI: 10.1073/pnas.1619806114] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Dimeric tubulin, an abundant water-soluble cytosolic protein known primarily for its role in the cytoskeleton, is routinely found to be associated with mitochondrial outer membranes, although the structure and physiological role of mitochondria-bound tubulin are still unknown. There is also no consensus on whether tubulin is a peripheral membrane protein or is integrated into the outer mitochondrial membrane. Here the results of five independent techniques-surface plasmon resonance, electrochemical impedance spectroscopy, bilayer overtone analysis, neutron reflectometry, and molecular dynamics simulations-suggest that α-tubulin's amphipathic helix H10 is responsible for peripheral binding of dimeric tubulin to biomimetic "mitochondrial" membranes in a manner that differentiates between the two primary lipid headgroups found in mitochondrial membranes, phosphatidylethanolamine and phosphatidylcholine. The identification of the tubulin dimer orientation and membrane-binding domain represents an essential step toward our understanding of the complex mechanisms by which tubulin interacts with integral proteins of the mitochondrial outer membrane and is important for the structure-inspired design of tubulin-targeting agents.
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Affiliation(s)
- David P Hoogerheide
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899;
| | - Sergei Y Noskov
- Center for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4;
| | - Daniel Jacobs
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Lucie Bergdoll
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
| | - Vitalii Silin
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899
- Institute for Bioscience and Biotechnology Research, University of Maryland, Rockville, MD 20850
| | - David L Worcester
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899
| | - Jeff Abramson
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
- Institute for Stem Cell Biology and Regenerative Medicine, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, Karnataka, India
| | - Hirsh Nanda
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899
- Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Tatiana K Rostovtseva
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Sergey M Bezrukov
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892;
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17
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Thompson PM, Ramachandran S, Case LB, Tolbert CE, Tandon A, Pershad M, Dokholyan NV, Waterman CM, Campbell SL. A Structural Model for Vinculin Insertion into PIP 2-Containing Membranes and the Effect of Insertion on Vinculin Activation and Localization. Structure 2017; 25:264-275. [PMID: 28089450 DOI: 10.1016/j.str.2016.12.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 11/10/2016] [Accepted: 12/12/2016] [Indexed: 12/20/2022]
Abstract
Vinculin, a scaffolding protein that localizes to focal adhesions (FAs) and adherens junctions, links the actin cytoskeleton to the adhesive super-structure. While vinculin binds to a number of cytoskeletal proteins, it can also associate with phosphatidylinositol 4,5-bisphosphate (PIP2) to drive membrane association. To generate a structural model for PIP2-dependent interaction of vinculin with the lipid bilayer, we conducted lipid-association, nuclear magnetic resonance, and computational modeling experiments. We find that two basic patches on the vinculin tail drive membrane association: the basic collar specifically recognizes PIP2, while the basic ladder drives association with the lipid bilayer. Vinculin mutants with defects in PIP2-dependent liposome association were then expressed in vinculin knockout murine embryonic fibroblasts. Results from these analyses indicate that PIP2 binding is not required for localization of vinculin to FAs or FA strengthening, but is required for vinculin activation and turnover at FAs to promote its association with the force transduction FA nanodomain.
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Affiliation(s)
- Peter M Thompson
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Srinivas Ramachandran
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Lindsay B Case
- Cell Biology and Physiology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Caitlin E Tolbert
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Arpit Tandon
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Mihir Pershad
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Nikolay V Dokholyan
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Clare M Waterman
- Cell Biology and Physiology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Sharon L Campbell
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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18
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Gradziel CS, Jordan PA, Jewel D, Dufort FJ, Miller SJ, Chiles TC, Roberts MF. d-3-Deoxy-dioctanoylphosphatidylinositol induces cytotoxicity in human MCF-7 breast cancer cells via a mechanism that involves downregulation of the D-type cyclin-retinoblastoma pathway. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1861:1808-1815. [PMID: 27600289 PMCID: PMC5115159 DOI: 10.1016/j.bbalip.2016.09.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Revised: 08/24/2016] [Accepted: 09/01/2016] [Indexed: 11/29/2022]
Abstract
Phosphatidylinositol analogs (PIAs) were originally designed to bind competitively to the Akt PH domain and prevent membrane translocation and activation. d-3-Deoxy-dioctanoylphosphatidylinositol (d-3-deoxy-diC8PI), but not compounds with altered inositol stereochemistry (e.g., l-3-deoxy-diC8PI and l-3,5-dideoxy-diC8PI), is cytotoxic. However, high resolution NMR field cycling relaxometry shows that both cytotoxic and non-toxic PIAs bind to the Akt1 PH domain at the site occupied by the cytotoxic alkylphospholipid perifosine. This suggests that another mechanism for cytotoxicity must account for the difference in efficacy of the synthetic short-chain PIAs. In MCF-7 breast cancer cells, with little constitutively active Akt, d-3-deoxy-diC8PI (but not l-compounds) decreases viability concomitant with increased cleavage of PARP and caspase 9, indicative of apoptosis. d-3-Deoxy-diC8PI also induces a decrease in endogenous levels of cyclins D1 and D3 and blocks downstream retinoblastoma protein phosphorylation. siRNA-mediated depletion of cyclin D1, but not cyclin D3, reduces MCF-7 cell proliferation. Thus, growth arrest and cytotoxicity induced by the soluble d-3-deoxy-diC8PI occur by a mechanism that involves downregulation of the D-type cyclin-pRb pathway independent of its interaction with Akt. This ability to downregulate D-type cyclins contributes, at least in part, to the anti-proliferative activity of d-3-deoxy-diC8PI and may be a common feature of other cytotoxic phospholipids.
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Affiliation(s)
- Cheryl S Gradziel
- Department of Chemistry, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467, USA.
| | - Peter A Jordan
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT 06520, USA.
| | - Delilah Jewel
- Department of Chemistry, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467, USA.
| | - Fay J Dufort
- Department of Biology, Higgins Hall, 140 Commonwealth Avenue, Boston College, Chestnut Hill, MA, USA.
| | - Scott J Miller
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT 06520, USA.
| | - Thomas C Chiles
- Department of Biology, Higgins Hall, 140 Commonwealth Avenue, Boston College, Chestnut Hill, MA, USA.
| | - Mary F Roberts
- Department of Chemistry, Boston College, 2609 Beacon Street, Chestnut Hill, MA 02467, USA.
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19
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Rosenberg MM, Redfield AG, Roberts MF, Hedstrom L. Substrate and Cofactor Dynamics on Guanosine Monophosphate Reductase Probed by High Resolution Field Cycling 31P NMR Relaxometry. J Biol Chem 2016; 291:22988-22998. [PMID: 27613871 PMCID: PMC5087720 DOI: 10.1074/jbc.m116.739516] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2016] [Revised: 08/31/2016] [Indexed: 12/31/2022] Open
Abstract
Guanosine-5'-monophosphate reductase (GMPR) catalyzes the reduction of GMP to IMP and ammonia with concomitant oxidation of NADPH. Here we investigated the structure and dynamics of enzyme-bound substrates and cofactors by measuring 31P relaxation rates over a large magnetic field range using high resolution field cycling NMR relaxometry. Surprisingly, these experiments reveal differences in the low field relaxation profiles for the monophosphate of GMP compared with IMP in their respective NADP+ complexes. These complexes undergo partial reactions that mimic different steps in the overall catalytic cycle. The relaxation profiles indicate that the substrate monophosphates have distinct interactions in E·IMP·NADP+ and E·GMP·NADP+ complexes. These findings were not anticipated by x-ray crystal structures, which show identical interactions for the monophosphates of GMP and IMP in several inert complexes. In addition, the motion of the cofactor is enhanced in the E·GMP·NADP+ complex. Last, the motions of the substrate and cofactor are coordinately regulated; the cofactor has faster local motions than GMP in the deamination complex but is more constrained than IMP in that complex, leading to hydride transfer. These results show that field cycling can be used to investigate the dynamics of protein-bound ligands and provide new insights into how portions of the substrate remote from the site of chemical transformation promote catalysis.
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Affiliation(s)
| | | | - Mary F Roberts
- the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860
| | - Lizbeth Hedstrom
- From the Departments of Biology,
- Chemistry, Brandeis University, Waltham, Massachusetts 02453 and
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20
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Baylon JL, Vermaas JV, Muller MP, Arcario MJ, Pogorelov TV, Tajkhorshid E. Atomic-level description of protein-lipid interactions using an accelerated membrane model. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1858:1573-83. [PMID: 26940626 PMCID: PMC4877275 DOI: 10.1016/j.bbamem.2016.02.027] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Revised: 02/19/2016] [Accepted: 02/20/2016] [Indexed: 01/03/2023]
Abstract
Peripheral membrane proteins are structurally diverse proteins that are involved in fundamental cellular processes. Their activity of these proteins is frequently modulated through their interaction with cellular membranes, and as a result techniques to study the interfacial interaction between peripheral proteins and the membrane are in high demand. Due to the fluid nature of the membrane and the reversibility of protein-membrane interactions, the experimental study of these systems remains a challenging task. Molecular dynamics simulations offer a suitable approach to study protein-lipid interactions; however, the slow dynamics of the lipids often prevents sufficient sampling of specific membrane-protein interactions in atomistic simulations. To increase lipid dynamics while preserving the atomistic detail of protein-lipid interactions, in the highly mobile membrane-mimetic (HMMM) model the membrane core is replaced by an organic solvent, while short-tailed lipids provide a nearly complete representation of natural lipids at the organic solvent/water interface. Here, we present a brief introduction and a summary of recent applications of the HMMM to study different membrane proteins, complementing the experimental characterization of the presented systems, and we offer a perspective of future applications of the HMMM to study other classes of membrane proteins. This article is part of a Special Issue entitled: Membrane proteins edited by J.C. Gumbart and Sergei Noskov.
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Affiliation(s)
- Javier L Baylon
- Center for Biophysics and Quantitative Biology; Beckman Institute for Advanced Science and Technology.
| | - Josh V Vermaas
- Center for Biophysics and Quantitative Biology; Beckman Institute for Advanced Science and Technology.
| | - Melanie P Muller
- Center for Biophysics and Quantitative Biology; Beckman Institute for Advanced Science and Technology; College of Medicine.
| | - Mark J Arcario
- Center for Biophysics and Quantitative Biology; Beckman Institute for Advanced Science and Technology; College of Medicine.
| | - Taras V Pogorelov
- Beckman Institute for Advanced Science and Technology; School of Chemical Sciences; Department of Chemistry; National Center for Supercomputing Applications.
| | - Emad Tajkhorshid
- Center for Biophysics and Quantitative Biology; Beckman Institute for Advanced Science and Technology; College of Medicine; Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
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21
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Monje-Galvan V, Klauda JB. Peripheral membrane proteins: Tying the knot between experiment and computation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1584-93. [PMID: 26903211 DOI: 10.1016/j.bbamem.2016.02.018] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 02/05/2016] [Accepted: 02/12/2016] [Indexed: 01/31/2023]
Abstract
Experimental biology has contributed to answer questions about the morphology of a system and how molecules organize themselves to maintain a healthy functional cell. Single-molecule techniques, optical and magnetic experiments, and fluorescence microscopy have come a long way to probe structural and dynamical information at multiple scales. However, some details are simply too small or the processes are too short-lived to detect by experiments. Computational biology provides a bridge to understand experimental results at the molecular level, makes predictions that have not been seen in vivo, and motivates new fields of research. This review focuses on the advances on peripheral membrane proteins (PMPs) studies; what is known about their interaction with membranes, their role in cell biology, and some limitations that both experiment and computation still have to overcome to gain better structural and functional understanding of these PMPs. As many recent reviews have acknowledged, interdisciplinary efforts between experiment and computation are needed in order to have useful models that lead future directions in the study of PMPs. We present new results of a case study on a PMP that behaves as an intricate machine controlling lipid homeostasis between cellular organelles, Osh4 in yeast Saccharomyces cerevisiae. Molecular dynamics simulations were run to examine the interaction between the protein and membrane models that reflect the lipid diversity of the endoplasmic reticulum and trans-Golgi membranes. Our study is consistent with experimental data showing several residues that interact to smaller or larger extent with the bilayer upon stable binding (~200 ns into the trajectory). We identified PHE239 as a key residue stabilizing the protein-membrane interaction along with two other binding regions, the ALPS-like motif and the β6-β7 loops in the mouth region of the protein. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.
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Affiliation(s)
- Viviana Monje-Galvan
- Department of Chemical and Biomolecular Engineering, College Park, MD 20742, USA
| | - Jeffery B Klauda
- Department of Chemical and Biomolecular Engineering, College Park, MD 20742, USA; Biophysics Program, University of Maryland, College Park, MD 20742, USA.
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22
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He T, Gershenson A, Eyles SJ, Lee YJ, Liu WR, Wang J, Gao J, Roberts MF. Fluorinated Aromatic Amino Acids Distinguish Cation-π Interactions from Membrane Insertion. J Biol Chem 2015; 290:19334-42. [PMID: 26092728 DOI: 10.1074/jbc.m115.668343] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Indexed: 01/02/2023] Open
Abstract
Cation-π interactions, where protein aromatic residues supply π systems while a positive-charged portion of phospholipid head groups are the cations, have been suggested as important binding modes for peripheral membrane proteins. However, aromatic amino acids can also insert into membranes and hydrophobically interact with lipid tails. Heretofore there has been no facile way to differentiate these two types of interactions. We show that specific incorporation of fluorinated amino acids into proteins can experimentally distinguish cation-π interactions from membrane insertion of the aromatic side chains. Fluorinated aromatic amino acids destabilize the cation-π interactions by altering electrostatics of the aromatic ring, whereas their increased hydrophobicity enhances membrane insertion. Incorporation of pentafluorophenylalanine or difluorotyrosine into a Staphylococcus aureus phosphatidylinositol-specific phospholipase C variant engineered to contain a specific PC-binding site demonstrates the effectiveness of this methodology. Applying this methodology to the plethora of tyrosine residues in Bacillus thuringiensis phosphatidylinositol-specific phospholipase C definitively identifies those involved in cation-π interactions with phosphatidylcholine. This powerful method can easily be used to determine the roles of aromatic residues in other peripheral membrane proteins and in integral membrane proteins.
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Affiliation(s)
- Tao He
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467
| | - Anne Gershenson
- Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, Amherst, Massachusetts 01003
| | - Stephen J Eyles
- Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, Amherst, Massachusetts 01003
| | - Yan-Jiun Lee
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, and
| | - Wenshe R Liu
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, and
| | - Jiangyun Wang
- Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China
| | - Jianmin Gao
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467
| | - Mary F Roberts
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467,
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23
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Wei Y, Stec B, Redfield AG, Weerapana E, Roberts MF. Phospholipid-binding sites of phosphatase and tensin homolog (PTEN): exploring the mechanism of phosphatidylinositol 4,5-bisphosphate activation. J Biol Chem 2014; 290:1592-606. [PMID: 25429968 DOI: 10.1074/jbc.m114.588590] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The lipid phosphatase activity of the tumor suppressor phosphatase and tensin homolog (PTEN) is enhanced by the presence of its biological product, phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). This enhancement is suggested to occur via the product binding to the N-terminal region of the protein. PTEN effects on short-chain phosphoinositide (31)P linewidths and on the full field dependence of the spin-lattice relaxation rate (measured by high resolution field cycling (31)P NMR using spin-labeled protein) are combined with enzyme kinetics with the same short-chain phospholipids to characterize where PI(4,5)P2 binds on the protein. The results are used to model a discrete site for a PI(4,5)P2 molecule close to, but distinct from, the active site of PTEN. This PI(4,5)P2 site uses Arg-47 and Lys-13 as phosphate ligands, explaining why PTEN R47G and K13E can no longer be activated by that phosphoinositide. Placing a PI(4,5)P2 near the substrate site allows for proper orientation of the enzyme on interfaces and should facilitate processive catalysis.
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Affiliation(s)
- Yang Wei
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467 and
| | - Boguslaw Stec
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467 and
| | - Alfred G Redfield
- the Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454
| | - Eranthie Weerapana
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467 and
| | - Mary F Roberts
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467 and
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24
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Jones LH, Narayanan A, Hett EC. Understanding and applying tyrosine biochemical diversity. MOLECULAR BIOSYSTEMS 2014; 10:952-69. [PMID: 24623162 DOI: 10.1039/c4mb00018h] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
This review highlights some of the recent advances made in our understanding of the diversity of tyrosine biochemistry and shows how this has inspired novel applications in numerous areas of molecular design and synthesis, including chemical biology and bioconjugation. The pathophysiological implications of tyrosine biochemistry will be presented from a molecular perspective and the opportunities for therapeutic intervention explored.
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Affiliation(s)
- Lyn H Jones
- Pfizer R&D, Chemical Biology Group, BioTherapeutics Chemistry, WorldWide Medicinal Chemistry, 200 Cambridge Park Drive, Cambridge, MA 02140, USA.
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25
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Gradziel CS, Wang Y, Stec B, Redfield AG, Roberts MF. Cytotoxic amphiphiles and phosphoinositides bind to two discrete sites on the Akt1 PH domain. Biochemistry 2014; 53:462-72. [PMID: 24383815 DOI: 10.1021/bi401720v] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The mechanism of binding of two promising anticancer agents (the cytotoxic alkylphospholipids perifosine and miltefosine) to the Akt PH domain is investigated by high-resolution field-cycling (31)P nuclear magnetic resonance (NMR) spectroscopy using a spin-labeled recombinant PH domain. These results strongly indicate that there are two discrete amphiphile binding sites on the domain: (i) the cationic site that binds phosphoinositides and some alkylphospholipids and (ii) a second site that is occupied by only the alkylphospholipids. The identification of this second site for amphiphiles on the Akt1 PH domain provides a new target for drug development as well as insights into the regulation of the activity of the intact Akt1 protein. The field-cycling NMR methodology could be used to define discrete phospholipid or amphiphile binding sites on a wide variety of peripheral membrane proteins.
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Affiliation(s)
- Cheryl S Gradziel
- Department of Chemistry, Boston College , Chestnut Hill, Massachusetts 02467, United States
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26
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Cai J, Guo S, Lomasney JW, Roberts MF. Ca2+-independent binding of anionic phospholipids by phospholipase C δ1 EF-hand domain. J Biol Chem 2013; 288:37277-88. [PMID: 24235144 DOI: 10.1074/jbc.m113.512186] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recombinant EF-hand domain of phospholipase C δ1 has a moderate affinity for anionic phospholipids in the absence of Ca(2+) that is driven by interactions of cationic and hydrophobic residues in the first EF-hand sequence. This region of PLC δ1 is missing in the crystal structure. The relative orientation of recombinant EF with respect to the bilayer, established with NMR methods, shows that the N-terminal helix of EF-1 is close to the membrane interface. Specific mutations of EF-1 residues in full-length PLC δ1 reduce enzyme activity but not because of disturbing partitioning of the protein onto vesicles. The reduction in enzymatic activity coupled with vesicle binding studies are consistent with a role for this domain in aiding substrate binding in the active site once the protein is transiently anchored at its target membrane.
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Affiliation(s)
- Jingfei Cai
- From the Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467 and
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27
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Grauffel C, Yang B, He T, Roberts MF, Gershenson A, Reuter N. Cation-π interactions as lipid-specific anchors for phosphatidylinositol-specific phospholipase C. J Am Chem Soc 2013; 135:5740-50. [PMID: 23506313 PMCID: PMC3797534 DOI: 10.1021/ja312656v] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Amphitropic proteins, such as the virulence factor phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus thuringiensis , often depend on lipid-specific recognition of target membranes. However, the recognition mechanisms for zwitterionic lipids, such as phosphatidylcholine, which is enriched in the outer leaflet of eukaryotic cells, are not well understood. A 500 ns long molecular dynamics simulation of PI-PLC at the surface of a lipid bilayer revealed a strikingly high number of interactions between tyrosines at the interfacial binding site and lipid choline groups with structures characteristic of cation-π interactions. Membrane affinities of PI-PLC tyrosine variants mostly tracked the simulation results, falling into two classes: (i) those with minor losses in affinity, Kd(mutant)/Kd(wild-type) ≤ 5 and (ii) those where the apparent Kd was 50-200 times higher than wild-type. Estimating ΔΔG for these Tyr/PC interactions from the apparent Kd values reveals that the free energy associated with class I is ~1 kcal/mol, comparable to the value predicted by the Wimley-White hydrophobicity scale. In contrast, removal of class II tyrosines has a higher energy cost: ~2.5 kcal/mol toward pure PC vesicles. These higher energies correlate well with the occupancy of the cation-π adducts throughout the MD simulation. Together, these results strongly indicate that PI-PLC interacts with PC headgroups via cation-π interactions with tyrosine residues and suggest that cation-π interactions at the interface may be a mechanism for specific lipid recognition by amphitropic and membrane proteins.
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Affiliation(s)
- Cédric Grauffel
- Department of Molecular Biology, University of Bergen, Norway
- Computational Biology Unit, Uni Research, Bergen, Norway
| | - Boqian Yang
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, U.S.A
- Department of Chemistry, Boston College, Chestnut Hill, U.S.A
| | - Tao He
- Department of Chemistry, Boston College, Chestnut Hill, U.S.A
| | - Mary F. Roberts
- Department of Chemistry, Boston College, Chestnut Hill, U.S.A
| | - Anne Gershenson
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, U.S.A
| | - Nathalie Reuter
- Department of Molecular Biology, University of Bergen, Norway
- Computational Biology Unit, Uni Research, Bergen, Norway
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Cheng J, Goldstein R, Gershenson A, Stec B, Roberts MF. The cation-π box is a specific phosphatidylcholine membrane targeting motif. J Biol Chem 2013; 288:14863-73. [PMID: 23576432 DOI: 10.1074/jbc.m113.466532] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Peripheral membrane proteins can be targeted to specific organelles or the plasma membrane by differential recognition of phospholipid headgroups. Although molecular determinants of specificity for several headgroups, including phosphatidylserine and phosphoinositides are well defined, specific recognition of the headgroup of the zwitterionic phosphatidylcholine (PC) is less well understood. In cytosolic proteins the cation-π box provides a suitable receptor for choline recognition and binding through the trimethylammonium moiety. In PC, this moiety might provide a sufficient handle to bind to peripheral proteins via a cation-π cage, where the π systems of two or more aromatic residues are within 4-5 Å of the quaternary amine. We prove this hypothesis by engineering the cation-π box into secreted phosphatidylinositol-specific phospholipase C from Staphylococcus aureus, which lacks specific PC recognition. The N254Y/H258Y variant selectively binds PC-enriched vesicles, and x-ray crystallography reveals N254Y/H258Y binds choline and dibutyroylphosphatidylcholine within the cation-π motif. Such simple PC recognition motifs could be engineered into a wide variety of secondary structures providing a generally applicable method for specific recognition of PC.
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Affiliation(s)
- Jiongjia Cheng
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, USA
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Cheng J, Karri S, Grauffel C, Wang F, Reuter N, Roberts MF, Wintrode PL, Gershenson A. Does changing the predicted dynamics of a phospholipase C alter activity and membrane binding? Biophys J 2013; 104:185-95. [PMID: 23332071 DOI: 10.1016/j.bpj.2012.11.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 11/02/2012] [Accepted: 11/19/2012] [Indexed: 12/11/2022] Open
Abstract
The enzymatic activity of secreted phosphatidylinositol-specific phospholipase C (PI-PLC) enzymes is associated with bacterial virulence. Although the PI-PLC active site has no obvious lid, molecular-dynamics simulations suggest that correlated loop motions may limit access to the active site, and two Pro residues, Pro(245) and Pro(254), are associated with these correlated motions. Whereas the region containing both Pro residues is quite variable among PI-PLCs, it shows high conservation in virulence-associated, secreted PI-PLCs that bind to the surface of cells. These regions of the protein are also associated with phosphatidylcholine binding, which enhances PI-PLC activity. In silico mutagenesis of Pro(245) disrupts correlated motions between the two halves of Bacillus thuringiensis PI-PLC, and Pro(245) variants show significantly reduced enzymatic activity in all assay systems. PC still enhanced activity, but not to the level of wild-type enzyme. Mutagenesis of Pro(254) appears to stiffen the PI-PLC structure, but experimental mutations had minor effects on activity and membrane binding. With the exception of P245Y, reduced activity was not associated with reduced membrane affinity. This combination of simulations and experiments suggests that correlated motions between the two halves of PI-PLC may be more important for enzymatic activity than for vesicle binding.
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Affiliation(s)
- Jiongjia Cheng
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts, USA
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Membrane-Binding Mechanism of a Peripheral Membrane Protein through Microsecond Molecular Dynamics Simulations. J Mol Biol 2012; 423:847-61. [DOI: 10.1016/j.jmb.2012.08.015] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Revised: 08/16/2012] [Accepted: 08/20/2012] [Indexed: 11/22/2022]
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31
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Cheng J, Goldstein R, Stec B, Gershenson A, Roberts MF. Competition between anion binding and dimerization modulates Staphylococcus aureus phosphatidylinositol-specific phospholipase C enzymatic activity. J Biol Chem 2012; 287:40317-27. [PMID: 23038258 DOI: 10.1074/jbc.m112.395277] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND Bacterial phosphatidylinositol-specific phospholipase C targets PI and glycosylphosphatidylinositol-linked proteins of eukaryotic cells. RESULTS Functional relevance of a homodimeric S. aureus PI-PLC crystal structure is supported by enzyme kinetics and mutagenesis. Nonsubstrate phosphatidylcholine increases activity by facilitating enzyme dimerization. CONCLUSION Activating transient dimerization is antagonized by anions binding to a discrete site. SIGNIFICANCE Interplay of protein oligomerization and anion binding controls enzyme activity. Staphylococcus aureus phosphatidylinositol-specific phospholipase C (PI-PLC) is a secreted virulence factor for this pathogenic bacterium. A novel crystal structure shows that this PI-PLC can form a dimer via helix B, a structural feature present in all secreted, bacterial PI-PLCs that is important for membrane binding. Despite the small size of this interface, it is critical for optimal enzyme activity. Kinetic evidence, increased enzyme specific activity with increasing enzyme concentration, supports a mechanism where the PI-PLC dimerization is enhanced in membranes containing phosphatidylcholine (PC). Mutagenesis of key residues confirm that the zwitterionic phospholipid acts not by specific binding to the protein, but rather by reducing anionic lipid interactions with a cationic pocket on the surface of the S. aureus enzyme that stabilizes monomeric protein. Despite its structural and sequence similarity to PI-PLCs from other Gram-positive pathogenic bacteria, S. aureus PI-PLC appears to have a unique mechanism where enzyme activity is modulated by competition between binding of soluble anions or anionic lipids to the cationic sensor and transient dimerization on the membrane.
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Affiliation(s)
- Jiongjia Cheng
- Department of Chemistry, Boston College, Chestnut Hill, MA 02467, USA
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Goñi FM, Montes LR, Alonso A. Phospholipases C and sphingomyelinases: Lipids as substrates and modulators of enzyme activity. Prog Lipid Res 2012; 51:238-66. [DOI: 10.1016/j.plipres.2012.03.002] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 03/23/2012] [Accepted: 03/26/2012] [Indexed: 11/30/2022]
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Goldstein R, Cheng J, Stec B, Roberts MF. Structure of the S. aureus PI-specific phospholipase C reveals modulation of active site access by a titratable π-cation latched loop. Biochemistry 2012; 51:2579-87. [PMID: 22390775 DOI: 10.1021/bi300057q] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Staphylococcus aureus secretes a phosphatidylinositol-specific phospholipase C (PI-PLC) as a virulence factor that is unusual in exhibiting higher activity at acidic pH values than other enzymes in this class. We have determined the crystal structure of this enzyme at pH 4.6 and pH 7.5. Under slightly basic conditions, the S. aureus PI-PLC structure closely follows the conformation of other bacterial PI-PLCs. However, when crystallized under acidic conditions, a large section of mobile loop at the αβ-barrel rim in the vicinity of the active site shows ~10 Å shift. This loop displacement at acidic pH is the result of a titratable intramolecular π-cation interaction between His258 and Phe249. This was verified by a structure of the mutant protein H258Y crystallized at pH 4.6, which does not exhibit the large loop shift. The intramolecular π-cation interaction for S. aureus PI-PLC provides an explanation for the activity of the enzyme at acid pH and also suggests how phosphatidylcholine, as a competitor for Phe249, may kinetically activate this enzyme.
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Affiliation(s)
- Rebecca Goldstein
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States
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Redfield AG. High-resolution NMR field-cycling device for full-range relaxation and structural studies of biopolymers on a shared commercial instrument. JOURNAL OF BIOMOLECULAR NMR 2012; 52:159-177. [PMID: 22200887 DOI: 10.1007/s10858-011-9594-1] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2011] [Accepted: 12/05/2011] [Indexed: 05/31/2023]
Abstract
Improvements are described in a shuttling field-cycling device (Redfield in Magn Reson Chem 41:753-768, 2003), designed to allow widespread access to this useful technique by configuring it as a removable module to a commercial 500 MHz NMR instrument. The main improvements described here, leading to greater versatility, high reliability and simple construction, include: shuttling provided by a linear motor driven by an integrated-control servomotor; provision of automated bucking magnets to allow fast two-stage cycling to nearly zero field; and overall control by a microprocessor. A brief review of history and publications that have used the system is followed by a discussion of topics related to such a device including discussion of some future applications. A description of new aspects of the shuttling device follows. The minimum round trip time to 1T and above is less than 0.25 s and to 0.002 T is 0.36 s. Commercial probes are used and sensitivity is that of the host spectrometer reduced only by relaxation during travel. A key element is development of a linkage that prevents vibration of the linear motor from reaching the probe.
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Affiliation(s)
- Alfred G Redfield
- Biochemistry Department, Brandeis University, Mail stop 009, Waltham, MA 02154, USA.
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Chou CY, Chu M, Chang CF, Huang TH. A compact high-speed mechanical sample shuttle for field-dependent high-resolution solution NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 214:302-8. [PMID: 22200566 DOI: 10.1016/j.jmr.2011.12.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2011] [Revised: 11/16/2011] [Accepted: 12/02/2011] [Indexed: 05/22/2023]
Abstract
Analysis of NMR relaxation data has provided significant insight on molecular dynamic, leading to a more comprehensive understanding of macromolecular functions. However, traditional methodology allows relaxation measurements performed only at a few fixed high fields, thus severely restricting their potential for extracting more complete dynamic information. Here we report the design and performance of a compact high-speed servo-mechanical shuttle assembly adapted to a commercial 600 MHz high-field superconducting magnet. The assembly is capable of shuttling the sample in a regular NMR tube from the center of the magnet to the top (fringe field ∼0.01 T) in 100 ms with no loss of sensitivity other than that due to intrinsic relaxation. The shuttle device can be installed by a single experienced user in 30 min. Excellent 2D-(15)N-HSQC spectra of (u-(13)C, (15)N)-ubiquitin with relaxation at low fields (3.77 T) and detection at 14.1T were obtained to illustrate its utility in R(1) measurements of macromolecules at low fields. Field-dependent (13)C-R(1) data of (3,3,3-d)-alanine at various field strengths were determined and analyzed to assess CSA and (1)H-(13)C dipolar contributions to the carboxyl (13)C-R(1).
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Affiliation(s)
- Ching-Yu Chou
- Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan, ROC
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