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Guo C, Cheng M, Li W, Gross ML. Precursor Reagent Hydrophobicity Affects Membrane Protein Footprinting. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023; 34:2700-2710. [PMID: 37967285 PMCID: PMC10924779 DOI: 10.1021/jasms.3c00272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2023]
Abstract
Membrane proteins (MPs) play a crucial role in cell signaling, molecular transport, and catalysis and thus are at the heart of designing pharmacological targets. Although structural characterization of MPs at the molecular level is essential to elucidate their biological function, it poses a significant challenge for structural biology. Although mass spectrometry-based protein footprinting may be developed into a powerful approach for studying MPs, the hydrophobic character of membrane regions makes structural characterization difficult using water-soluble footprinting reagents. Herein, we evaluated a small series of MS-based photoactivated iodine reagents with different hydrophobicities. We used tip sonication to facilitate diffusion into micelles, thus enhancing reagent access to the hydrophobic core of MPs. Quantification of the modification extent in hydrophilic extracellular and hydrophobic transmembrane domains provides structurally sensitive information at the residue-level as measured by proteolysis and LC-MS/MS for a model MP, vitamin K epoxide reductase (VKOR). It also reveals a relationship between the reagent hydrophobicity and its preferential labeling sites in the local environment. The outcome should guide the future development of chemical probes for MPs and promote a direction for relatively high-throughput information-rich characterization of MPs in biochemistry and drug discovery.
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2
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Reid DJ, Dash T, Wang Z, Aspinwall CA, Marty MT. Investigating Daptomycin-Membrane Interactions Using Native MS and Fast Photochemical Oxidation of Peptides in Nanodiscs. Anal Chem 2023; 95:4984-4991. [PMID: 36888920 PMCID: PMC10033427 DOI: 10.1021/acs.analchem.2c05222] [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] [Indexed: 03/10/2023]
Abstract
Daptomycin is a cyclic lipopeptide antibiotic that targets the lipid membrane of Gram-positive bacteria. Membrane fluidity and charge can affect daptomycin activity, but its mechanisms are poorly understood because it is challenging to study daptomycin interactions within lipid bilayers. Here, we combined native mass spectrometry (MS) and fast photochemical oxidation of peptides (FPOP) to study daptomycin-membrane interactions with different lipid bilayer nanodiscs. Native MS suggests that daptomycin incorporates randomly and does not prefer any specific oligomeric states when integrated into bilayers. FPOP reveals significant protection in most bilayer environments. Combining the native MS and FPOP results, we observed that stronger membrane interactions are formed with more rigid membranes, and pore formation may occur in more fluid membranes to expose daptomycin to FPOP oxidation. Electrophysiology measurements further supported the observation of polydisperse pore complexes from the MS data. Together, these results demonstrate the complementarity of native MS, FPOP, and membrane conductance experiments to shed light on how antibiotic peptides interact with and within lipid membranes.
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Affiliation(s)
- Deseree J. Reid
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Tapasyatanu Dash
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Zhihan Wang
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Craig A. Aspinwall
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
- Bio5 Institute, University of Arizona, Tucson, AZ 85721, USA
| | - Michael T. Marty
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
- Bio5 Institute, University of Arizona, Tucson, AZ 85721, USA
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3
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Dafun AS, Marcoux J. Structural mass spectrometry of membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA. PROTEINS AND PROTEOMICS 2022; 1870:140813. [PMID: 35750312 DOI: 10.1016/j.bbapap.2022.140813] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 06/10/2022] [Accepted: 06/17/2022] [Indexed: 06/15/2023]
Abstract
The analysis of proteins and protein complexes by mass spectrometry (MS) has come a long way since the invention of electrospray ionization (ESI) in the mid 80s. Originally used to characterize small soluble polypeptide chains, MS has progressively evolved over the past 3 decades towards the analysis of samples of ever increasing heterogeneity and complexity, while the instruments have become more and more sensitive and resolutive. The proofs of concepts and first examples of most structural MS methods appeared in the early 90s. However, their application to membrane proteins, key targets in the biopharma industry, is more recent. Nowadays, a wealth of information can be gathered from such MS-based methods, on all aspects of membrane protein structure: sequencing (and more precisely proteoform characterization), but also stoichiometry, non-covalent ligand binding (metals, drug, lipids, carbohydrates), conformations, dynamics and distance restraints for modelling. In this review, we present the concept and some historical and more recent applications on membrane proteins, for the major structural MS methods.
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Affiliation(s)
- Angelique Sanchez Dafun
- Institut de Pharmacologie et de Biologie Structurale (IPBS), Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Julien Marcoux
- Institut de Pharmacologie et de Biologie Structurale (IPBS), Université de Toulouse, CNRS, UPS, Toulouse, France.
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4
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Pan X, Kirsch ZJ, Vachet RW. Distinguishing Histidine Tautomers in Proteins Using Covalent Labeling-Mass Spectrometry. Anal Chem 2022; 94:1003-1010. [PMID: 34962759 PMCID: PMC8787799 DOI: 10.1021/acs.analchem.1c03902] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
In this work, we use diethylpyrocarbonate (DEPC)-based covalent labeling together with LC-MS/MS analysis to distinguish the two sidechain tautomers of histidine residues in peptides and proteins. From labeling experiments on model peptides, we demonstrate that DEPC reacts equally with both tautomeric forms to produce chemically different products with distinct dissociation patterns and LC retention times, allowing the ratios of the two tautomers to be determined in peptides and proteins. Upon measuring the tautomer ratios of several histidine residues in myoglobin, we find good agreement with previous 2D NMR data on this protein. Because our DEPC labeling/MS approach is simpler, faster, and more precise than 2D NMR, our method will be a valuable way to determine how protein structure enforces histidine sidechain tautomerization. Because the tautomeric state of histidine residues is often important for protein structure and function, the ability of DEPC labeling/MS to distinguish histidine tautomers should equip researchers with a tool to understand the histidine residue structure and function more deeply in proteins.
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Reid DJ, Rohrbough JG, Kostelic MM, Marty MT. Investigating Antimicrobial Peptide-Membrane Interactions Using Fast Photochemical Oxidation of Peptides in Nanodiscs. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2022; 33:62-67. [PMID: 34866389 PMCID: PMC8732327 DOI: 10.1021/jasms.1c00252] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Antimicrobial peptides (AMPs) are an important part of the innate immune system and demonstrate promising applications in the fight against antibiotic-resistant infections due to their unique mechanism of targeting bacterial membranes. However, it is challenging to study the interactions of these peptides within lipid bilayers, making it difficult to understand their mechanisms of toxicity and selectivity. Here, we used fast photochemical oxidation of peptides, an irreversible footprinting technique that labels solvent accessible residues, and native charge detection-mass spectrometry to study AMP-lipid interactions with different lipid bilayer nanodiscs. We observed differences in the oxidation of two peptides, indolicidin and LL-37, in three distinct lipid environments, which reveal their affinity for lipid bilayers. Our findings suggest that indolicidin interacts with lipid head groups via a simple charge-driven mechanism, but LL-37 is more specific for Escherichia coli nanodiscs. These results provide complementary information on the potential modes of action and lipid selectivity of AMPs.
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Affiliation(s)
- Deseree J. Reid
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - James G. Rohrbough
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Marius M. Kostelic
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Michael T. Marty
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA
- Bio5 Institute, University of Arizona, Tucson, AZ 85721, USA
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6
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Pan X, Vachet RW. MEMBRANE PROTEIN STRUCTURES AND INTERACTIONS FROM COVALENT LABELING COUPLED WITH MASS SPECTROMETRY. MASS SPECTROMETRY REVIEWS 2022; 41:51-69. [PMID: 33145813 PMCID: PMC8093322 DOI: 10.1002/mas.21667] [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: 09/10/2020] [Revised: 10/15/2020] [Accepted: 10/16/2020] [Indexed: 05/31/2023]
Abstract
Membrane proteins are incredibly important biomolecules because they mediate interactions between a cell's external and internal environment. Obtaining information about membrane protein structure and interactions is thus important for understanding these essential biomolecules. Compared with the analyses of water-soluble proteins, the structural analysis of membrane proteins is more challenging owing to their unique chemical properties and the presence of lipid components that are necessary to solubilize them. The combination of covalent labeling (CL) and mass spectrometry (MS) has recently been applied with great success to study membrane protein structure and interactions. These studies have demonstrated the many advantages that CL-MS methods have over other traditional biophysical techniques. In this review, we discuss both amino acid-specific and non-specific labeling approaches and the special considerations needed to address the unique challenges associated with interrogating membrane proteins. This review highlights the aspects of this approach that require special care to be applied correctly and provides a comprehensive review of the membrane protein systems that have been studied by CL-MS. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.
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McKenzie-Coe A, Montes NS, Jones LM. Hydroxyl Radical Protein Footprinting: A Mass Spectrometry-Based Structural Method for Studying the Higher Order Structure of Proteins. Chem Rev 2021; 122:7532-7561. [PMID: 34633178 DOI: 10.1021/acs.chemrev.1c00432] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Hydroxyl radical protein footprinting (HRPF) coupled to mass spectrometry has been successfully used to investigate a plethora of protein-related questions. The method, which utilizes hydroxyl radicals to oxidatively modify solvent-accessible amino acids, can inform on protein interaction sites and regions of conformational change. Hydroxyl radical-based footprinting was originally developed to study nucleic acids, but coupling the method with mass spectrometry has enabled the study of proteins. The method has undergone several advancements since its inception that have increased its utility for more varied applications such as protein folding and the study of biotherapeutics. In addition, recent innovations have led to the study of increasingly complex systems including cell lysates and intact cells. Technological advances have also increased throughput and allowed for better control of experimental conditions. In this review, we provide a brief history of the field of HRPF and detail recent innovations and applications in the field.
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Affiliation(s)
- Alan McKenzie-Coe
- Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Maryland 21201, United States
| | - Nicholas S Montes
- Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Maryland 21201, United States
| | - Lisa M Jones
- Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Maryland 21201, United States
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8
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Liu XR, Zhang MM, Gross ML. Mass Spectrometry-Based Protein Footprinting for Higher-Order Structure Analysis: Fundamentals and Applications. Chem Rev 2020; 120:4355-4454. [PMID: 32319757 PMCID: PMC7531764 DOI: 10.1021/acs.chemrev.9b00815] [Citation(s) in RCA: 130] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Proteins adopt different higher-order structures (HOS) to enable their unique biological functions. Understanding the complexities of protein higher-order structures and dynamics requires integrated approaches, where mass spectrometry (MS) is now positioned to play a key role. One of those approaches is protein footprinting. Although the initial demonstration of footprinting was for the HOS determination of protein/nucleic acid binding, the concept was later adapted to MS-based protein HOS analysis, through which different covalent labeling approaches "mark" the solvent accessible surface area (SASA) of proteins to reflect protein HOS. Hydrogen-deuterium exchange (HDX), where deuterium in D2O replaces hydrogen of the backbone amides, is the most common example of footprinting. Its advantage is that the footprint reflects SASA and hydrogen bonding, whereas one drawback is the labeling is reversible. Another example of footprinting is slow irreversible labeling of functional groups on amino acid side chains by targeted reagents with high specificity, probing structural changes at selected sites. A third footprinting approach is by reactions with fast, irreversible labeling species that are highly reactive and footprint broadly several amino acid residue side chains on the time scale of submilliseconds. All of these covalent labeling approaches combine to constitute a problem-solving toolbox that enables mass spectrometry as a valuable tool for HOS elucidation. As there has been a growing need for MS-based protein footprinting in both academia and industry owing to its high throughput capability, prompt availability, and high spatial resolution, we present a summary of the history, descriptions, principles, mechanisms, and applications of these covalent labeling approaches. Moreover, their applications are highlighted according to the biological questions they can answer. This review is intended as a tutorial for MS-based protein HOS elucidation and as a reference for investigators seeking a MS-based tool to address structural questions in protein science.
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Affiliation(s)
| | | | - Michael L. Gross
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA, 63130
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Shi L, Gross ML. Fast Photochemical Oxidation of Proteins Coupled with Mass Spectrometry. Protein Pept Lett 2019; 26:27-34. [PMID: 30484399 DOI: 10.2174/0929866526666181128124554] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 08/30/2018] [Accepted: 09/27/2018] [Indexed: 11/22/2022]
Abstract
BACKGROUND Determination of the composition and some structural features of macromolecules can be achieved by using structural proteomics approaches coupled with mass spectrometry (MS). One approach is hydroxyl radical protein footprinting whereby amino-acid side chains are modified with reactive reagents to modify irreversibly a protein side chain. The outcomes, when deciphered with mass-spectrometry-based proteomics, can increase our knowledge of structure, assembly, and conformational dynamics of macromolecules in solution. Generating the hydroxyl radicals by laser irradiation, Hambly and Gross developed the approach of Fast Photochemical Oxidation of Proteins (FPOP), which labels proteins on the sub millisecond time scale and provides, with MS analysis, deeper understanding of protein structure and protein-ligand and protein- protein interactions. This review highlights the fundamentals of FPOP and provides descriptions of hydroxyl-radical and other radical and carbene generation, of the hydroxyl labeling of proteins, and of determination of protein modification sites. We also summarize some recent applications of FPOP coupled with MS in protein footprinting. CONCLUSION We survey results that show the capability of FPOP for qualitatively measuring protein solvent accessibility on the residue level. To make these approaches more valuable, we describe recent method developments that increase FPOP's quantitative capacity and increase the spatial protein sequence coverage. To improve FPOP further, several new labeling reagents including carbenes and other radicals have been developed. These growing improvements will allow oxidative- footprinting methods coupled with MS to play an increasingly significant role in determining the structure and dynamics of macromolecules and their assemblies.
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Affiliation(s)
- Liuqing Shi
- Department of Chemistry, Washington University, St. Louis, MO 63130, United States
| | - Michael L Gross
- Department of Chemistry, Washington University, St. Louis, MO 63130, United States
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10
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Sharp JS, Misra SK, Persoff JJ, Egan RW, Weinberger SR. Real Time Normalization of Fast Photochemical Oxidation of Proteins Experiments by Inline Adenine Radical Dosimetry. Anal Chem 2018; 90:12625-12630. [PMID: 30290117 PMCID: PMC7811273 DOI: 10.1021/acs.analchem.8b02787] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Hydroxyl radical protein footprinting (HRPF) is a powerful method for measuring protein topography, allowing researchers to monitor events that alter the solvent accessible surface of a protein (e.g., ligand binding, aggregation, conformational changes, etc.) by measuring changes in the apparent rate of reaction of portions of the protein to hydroxyl radicals diffusing in solution. Fast Photochemical Oxidation of Proteins (FPOP) offers an ultrafast benchtop method for radical generation for HRPF, photolyzing hydrogen peroxide using a UV laser to generate high concentrations of hydroxyl radicals that are consumed on roughly a microsecond time scale. The broad reactivity of hydroxyl radicals means that almost anything added to the solution (e.g., ligands, buffers, excipients, etc.) will scavenge hydroxyl radicals, altering their half-life and changing the effective radical concentration experienced by the protein. Similarly, minute changes in peroxide concentration, laser fluence, and buffer composition can alter the effective radical concentration, making reproduction of data challenging. Here, we present a simple method for radical dosimetry that can be carried out as part of the FPOP workflow, allowing for measurement of effective radical concentration in real time. Additionally, by modulating the amount of radical generated, we demonstrate that effective hydroxyl radical yields in FPOP HRPF experiments carried out in buffers with widely differing levels of hydroxyl radical scavenging capacity can be compensated on the fly, yielding statistically indistinguishable results for the same conformer. This method represents a major step in transforming FPOP into a robust and reproducible technology capable of probing protein structure in a wide variety of contexts.
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Affiliation(s)
- Joshua S. Sharp
- Department of BioMolecular Sciences, University of Mississippi, Oxford, MS 38677
- GenNext Technologies, Inc., Montara, CA 94037
| | - Sandeep K. Misra
- Department of BioMolecular Sciences, University of Mississippi, Oxford, MS 38677
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11
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Calabrese AN, Radford SE. Mass spectrometry-enabled structural biology of membrane proteins. Methods 2018; 147:187-205. [DOI: 10.1016/j.ymeth.2018.02.020] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Revised: 01/30/2018] [Accepted: 02/21/2018] [Indexed: 01/01/2023] Open
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12
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Limpikirati P, Liu T, Vachet RW. Covalent labeling-mass spectrometry with non-specific reagents for studying protein structure and interactions. Methods 2018; 144:79-93. [PMID: 29630925 PMCID: PMC6051898 DOI: 10.1016/j.ymeth.2018.04.002] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Revised: 04/03/2018] [Accepted: 04/04/2018] [Indexed: 12/13/2022] Open
Abstract
Using mass spectrometry (MS) to obtain information about a higher order structure of protein requires that a protein's structural properties are encoded into the mass of that protein. Covalent labeling (CL) with reagents that can irreversibly modify solvent accessible amino acid side chains is an effective way to encode structural information into the mass of a protein, as this information can be read-out in a straightforward manner using standard MS-based proteomics techniques. The differential reactivity of proteins under two or more conditions can be used to distinguish protein topologies, conformations, and/or binding sites. CL-MS methods have been effectively used for the structural analysis of proteins and protein complexes, particularly for systems that are difficult to study by other more traditional biochemical techniques. This review provides an overview of the non-specific CL approaches that have been combined with MS with a particular emphasis on the reagents that are commonly used, including hydroxyl radicals, carbenes, and diethylpyrocarbonate. We describe the reagent and protein factors that affect the reactivity of amino acid side chains. We also include details about experimental design and workflow, data analysis, recent applications, and some future prospects of CL-MS methods.
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Affiliation(s)
| | - Tianying Liu
- Department of Chemistry, University of Massachusetts Amherst, MA 01003, United States
| | - Richard W Vachet
- Department of Chemistry, University of Massachusetts Amherst, MA 01003, United States.
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13
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Recent advances in biophysical studies of rhodopsins - Oligomerization, folding, and structure. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:1512-1521. [PMID: 28844743 DOI: 10.1016/j.bbapap.2017.08.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2017] [Revised: 08/06/2017] [Accepted: 08/11/2017] [Indexed: 12/19/2022]
Abstract
Retinal-binding proteins, mainly known as rhodopsins, function as photosensors and ion transporters in a wide range of organisms. From halobacterial light-driven proton pump, bacteriorhodopsin, to bovine photoreceptor, visual rhodopsin, they have served as prototypical α-helical membrane proteins in a large number of biophysical studies and aided in the development of many cutting-edge techniques of structural biology and biospectroscopy. In the last decade, microbial and animal rhodopsin families have expanded significantly, bringing into play a number of new interesting structures and functions. In this review, we will discuss recent advances in biophysical approaches to retinal-binding proteins, primarily microbial rhodopsins, including those in optical spectroscopy, X-ray crystallography, nuclear magnetic resonance, and electron paramagnetic resonance, as applied to such fundamental biological aspects as protein oligomerization, folding, and structure.
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14
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Kinzel J, Sauer DF, Bocola M, Arlt M, Mirzaei Garakani T, Thiel A, Beckerle K, Polen T, Okuda J, Schwaneberg U. 2-Methyl-2,4-pentanediol (MPD) boosts as detergent-substitute the performance of ß-barrel hybrid catalyst for phenylacetylene polymerization. Beilstein J Org Chem 2017; 13:1498-1506. [PMID: 28845193 PMCID: PMC5550818 DOI: 10.3762/bjoc.13.148] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 07/13/2017] [Indexed: 02/02/2023] Open
Abstract
Covering hydrophobic regions with stabilization agents to solubilize purified transmembrane proteins is crucial for their application in aqueous media. The small molecule 2-methyl-2,4-pentanediol (MPD) was used to stabilize the transmembrane protein Ferric hydroxamate uptake protein component A (FhuA) utilized as host for the construction of a rhodium-based biohybrid catalyst. Unlike commonly used detergents such as sodium dodecyl sulfate or polyethylene polyethyleneglycol, MPD does not form micelles in solution. Molecular dynamics simulations revealed the effect and position of stabilizing MPD molecules. The advantage of the amphiphilic MPD over micelle-forming detergents is demonstrated in the polymerization of phenylacetylene, showing a ten-fold increase in yield and increased molecular weights.
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Affiliation(s)
- Julia Kinzel
- Institute of Biotechnology, RWTH Aachen University, Worringer Weg 3, 52074 Aachen, Germany
| | - Daniel F Sauer
- Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | - Marco Bocola
- Institute of Biotechnology, RWTH Aachen University, Worringer Weg 3, 52074 Aachen, Germany
| | - Marcus Arlt
- Institute of Biotechnology, RWTH Aachen University, Worringer Weg 3, 52074 Aachen, Germany
| | - Tayebeh Mirzaei Garakani
- Institute of Biotechnology, RWTH Aachen University, Worringer Weg 3, 52074 Aachen, Germany.,DWI - Leibniz Institute for Interactive Materials e.V., Forckenbeckstr. 50, 52056, Aachen, Germany
| | - Andreas Thiel
- Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | - Klaus Beckerle
- Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | - Tino Polen
- Institute of Bio- und Geosciences, IBG-1: Biotechnology, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Jun Okuda
- Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | - Ulrich Schwaneberg
- Institute of Biotechnology, RWTH Aachen University, Worringer Weg 3, 52074 Aachen, Germany.,DWI - Leibniz Institute for Interactive Materials e.V., Forckenbeckstr. 50, 52056, Aachen, Germany
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15
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Fehr N, García-Rubio I, Jeschke G, Paulsen H. Early folding events during light harvesting complex II assembly in vitro monitored by pulsed electron paramagnetic resonance. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1857:695-704. [PMID: 27063475 DOI: 10.1016/j.bbabio.2016.04.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 03/16/2016] [Accepted: 04/06/2016] [Indexed: 12/20/2022]
Abstract
Efficient energy transfer in the major light harvesting complex II (LHCII) of green plants is facilitated by the precise alignment of pigments due to the protein matrix they are bound to. Much is known about the import of the LHCII apoprotein into the chloroplast via the TOC/TIC system and its targeting to the thylakoid membrane but information is sparse about when and where the pigments are bound and how this is coordinated with protein folding. In vitro, the LHCII apoprotein spontaneously folds and binds its pigments if the detergent-solubilized protein is combined with a mixture of chlorophylls a and b and carotenoids. In the present work, we employed this approach to study apoprotein folding and pigment binding in a time-resolved manner by using pulsed electron paramagnetic resonance (EPR). Intra-molecular distances were measured before folding, after 255 ms and 40 s folding time in the absence of cryoprotectant, and in the fully folded and assembled LHCII. In accordance with earlier results, the most of the folding of the three membrane-spanning alpha helices precedes their apposition into the final tertiary structure. However, their formation follows different kinetics, partially extending into the final phase of LHCII formation during which much of the condensation of the pigment-protein structure occurs, presumably governed by the binding of chlorophyll b. A rough timetable is proposed to sort partial events into the LHCII formation process.
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Affiliation(s)
- Niklas Fehr
- Department of General Botany, Johannes Gutenberg-University, 55128 Mainz, Germany
| | - Inés García-Rubio
- Department of Physical Chemistry, ETH Zurich, Vladimir Prelog-Weg 2, CH-8093, Zürich, Switzerland
| | - Gunnar Jeschke
- Department of Physical Chemistry, ETH Zurich, Vladimir Prelog-Weg 2, CH-8093, Zürich, Switzerland
| | - Harald Paulsen
- Department of General Botany, Johannes Gutenberg-University, 55128 Mainz, Germany.
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16
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Calabrese AN, Ault JR, Radford SE, Ashcroft AE. Using hydroxyl radical footprinting to explore the free energy landscape of protein folding. Methods 2015; 89:38-44. [PMID: 25746386 PMCID: PMC4651025 DOI: 10.1016/j.ymeth.2015.02.018] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 02/17/2015] [Accepted: 02/23/2015] [Indexed: 01/26/2023] Open
Abstract
Characterisation of the conformational states adopted during protein folding, including globally unfolded/disordered structures and partially folded intermediate species, is vital to gain fundamental insights into how a protein folds. In this work we employ fast photochemical oxidation of proteins (FPOP) to map the structural changes that occur in the folding of the four-helical bacterial immunity protein, Im7. Oxidative footprinting coupled with mass spectrometry (MS) is used to probe changes in the solvent accessibility of amino acid side-chains concurrent with the folding process, by quantifying the degree of oxidation experienced by the wild-type protein relative to a kinetically trapped, three-helical folding intermediate and an unfolded variant that lacks secondary structure. Analysis of the unfolded variant by FPOP-MS shows oxidative modifications consistent with the species adopting a solution conformation with a high degree of solvent accessibility. The folding intermediate, by contrast, experiences increased levels of oxidation relative to the wild-type, native protein only in regions destabilised by the amino acid substitutions introduced. The results demonstrate the utility of FPOP-MS to characterise protein variants in different conformational states and to provide insights into protein folding mechanisms that are complementary to measurements such as hydrogen/deuterium exchange labelling and Φ-value analysis.
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Affiliation(s)
- Antonio N Calabrese
- School of Molecular and Cellular Biology, Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - James R Ault
- School of Molecular and Cellular Biology, Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Sheena E Radford
- School of Molecular and Cellular Biology, Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
| | - Alison E Ashcroft
- School of Molecular and Cellular Biology, Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
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17
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Heinkel F, Gsponer J. Determination of Protein Folding Intermediate Structures Consistent with Data from Oxidative Footprinting Mass Spectrometry. J Mol Biol 2015; 428:365-371. [PMID: 26523679 DOI: 10.1016/j.jmb.2015.10.022] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Revised: 10/21/2015] [Accepted: 10/22/2015] [Indexed: 11/29/2022]
Abstract
The mapping of folding landscapes remains an important challenge in protein chemistry. Pulsed oxidative labeling of exposed residues and their detection via mass spectrometry provide new means of taking time-resolved "snapshots" of the structural changes that occur during protein folding. However, such experiments have been so far only interpreted qualitatively. Here, we report the detailed structural interpretation of mass spectrometry data from fast photochemical oxidation of proteins (FPOP) experiments at atomic resolution in a biased molecular dynamics approach. We are able to calculate structures of the early folding intermediate of the model system barstar that are fully consistent with FPOP data and Φ values. Furthermore, structures calculated with both FPOP data and Φ values are significantly less compact and have fewer helical residues than intermediate structures calculated with Φ values only. This improves the agreement with the experimental β-Tanford value and CD measurements. The restraints that we introduce facilitate the structural interpretation of FPOP data and provide new means for refined structure calculations of transiently sampled states on protein folding landscapes.
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Affiliation(s)
- Florian Heinkel
- Centre for High-Throughput Biology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Jörg Gsponer
- Centre for High-Throughput Biology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
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18
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Duc NM, Du Y, Zhang C, Lee SY, Thorsen TS, Kobilka BK, Chung KY. Effective application of bicelles for conformational analysis of G protein-coupled receptors by hydrogen/deuterium exchange mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:808-817. [PMID: 25740347 PMCID: PMC4727453 DOI: 10.1007/s13361-015-1083-4] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Revised: 01/15/2015] [Accepted: 01/16/2015] [Indexed: 06/04/2023]
Abstract
G protein-coupled receptors (GPCRs) have important roles in physiology and pathology, and 40% of drugs currently on the market target GPCRs for the treatment of various diseases. Because of their therapeutic importance, the structural mechanism of GPCR signaling is of great interest in the field of drug discovery. Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is a useful tool for analyzing ligand binding sites, the protein-protein interaction interface, and conformational changes of proteins. However, its application to GPCRs has been limited for various reasons, including the hydrophobic nature of GPCRs and the use of detergents in their preparation. In the present study, we tested the application of bicelles as a means of solubilizing GPCRs for HDX-MS studies. GPCRs (e.g., β2-adrenergic receptor [β2AR], μ-opioid receptor, and protease-activated receptor 1) solubilized in bicelles produced better sequence coverage (greater than 90%) than GPCRs solubilized in n-dodecyl-β-D-maltopyranoside (DDM), suggesting that bicelles are a more effective method of solubilization for HDX-MS studies. The HDX-MS profile of β2AR in bicelles showed that transmembrane domains (TMs) undergo lower deuterium uptake than intracellular or extracellular regions, which is consistent with the fact that the TMs are highly ordered and embedded in bicelles. The overall HDX-MS profiles of β2AR solubilized in bicelles and in DDM were similar except for intracellular loop 3. Interestingly, we detected EX1 kinetics, an important phenomenon in protein dynamics, at the C-terminus of TM6 in β2AR. In conclusion, we suggest the application of bicelles as a useful method for solubilizing GPCRs for conformational analysis by HDX-MS.
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MESH Headings
- Amino Acid Sequence
- Detergents/chemistry
- Deuterium Exchange Measurement
- Feasibility Studies
- Humans
- Kinetics
- Lipid Bilayers/chemistry
- Lipid Bilayers/metabolism
- Maltose/analogs & derivatives
- Maltose/chemistry
- Micelles
- Models, Molecular
- Molecular Sequence Data
- Protein Conformation
- Protein Folding
- Protein Structure, Tertiary
- Receptor, PAR-1/chemistry
- Receptor, PAR-1/genetics
- Receptor, PAR-1/metabolism
- Receptors, Adrenergic, beta-2/chemistry
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/metabolism
- Solubility
- Spectrometry, Mass, Electrospray Ionization
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Affiliation(s)
- Nguyen Minh Duc
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, South Korea
| | - Yang Du
- Department of Molecular and Cellular Physiology, Stanford University, Medical School, 297 Campus Drive, Beckman Center, Stanford, California, USA
| | - Cheng Zhang
- Department of Molecular and Cellular Physiology, Stanford University, Medical School, 297 Campus Drive, Beckman Center, Stanford, California, USA
| | - Su Youn Lee
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, South Korea
| | - Thor S. Thorsen
- Department of Molecular and Cellular Physiology, Stanford University, Medical School, 297 Campus Drive, Beckman Center, Stanford, California, USA
| | - Brian K Kobilka
- Department of Molecular and Cellular Physiology, Stanford University, Medical School, 297 Campus Drive, Beckman Center, Stanford, California, USA
| | - Ka Young Chung
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, South Korea
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19
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Schlebach J, Woodall N, Bowie JU, Park C. Bacteriorhodopsin folds through a poorly organized transition state. J Am Chem Soc 2014; 136:16574-81. [PMID: 25369295 PMCID: PMC4277764 DOI: 10.1021/ja508359n] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Indexed: 11/30/2022]
Abstract
The folding mechanisms of helical membrane proteins remain largely uncharted. Here we characterize the kinetics of bacteriorhodopsin folding and employ φ-value analysis to explore the folding transition state. First, we developed and confirmed a kinetic model that allowed us to assess the rate of folding from SDS-denatured bacteriorhodopsin (bRU) and provides accurate thermodynamic information even under influence of retinal hydrolysis. Next, we obtained reliable φ-values for 16 mutants of bacteriorhodopsin with good coverage across the protein. Every φ-value was less than 0.4, indicating the transition state is not uniquely structured. We suggest that the transition state is a loosely organized ensemble of conformations.
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Affiliation(s)
- Jonathan
P. Schlebach
- Department
of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 575
Stadium Mall Drive, West Lafayette, Indiana 47907, United
States
- Interdisciplinary
Life Science Graduate Program, Purdue University, 155 South Grant Street, West Lafayette, Indiana 47907, United States
| | - Nicholas
B. Woodall
- Department
of Chemistry and Biochemistry, University
of California, Los Angeles, 607 Charles E. Young Drive East, Box 951569, Los Angeles, California 90095-1569, United States
| | - James U. Bowie
- Department
of Chemistry and Biochemistry, University
of California, Los Angeles, 607 Charles E. Young Drive East, Box 951569, Los Angeles, California 90095-1569, United States
| | - Chiwook Park
- Department
of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 575
Stadium Mall Drive, West Lafayette, Indiana 47907, United
States
- Interdisciplinary
Life Science Graduate Program, Purdue University, 155 South Grant Street, West Lafayette, Indiana 47907, United States
- Bindley
Bioscience Center, Purdue University, 1203 West State Street, West Lafayette, Indiana 47907, United States
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20
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Liuni P, Zhu S, Wilson DJ. Oxidative protein labeling with analysis by mass spectrometry for the study of structure, folding, and dynamics. Antioxid Redox Signal 2014; 21:497-510. [PMID: 24512178 DOI: 10.1089/ars.2014.5850] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
SIGNIFICANCE Analytical approaches that can provide insights into the mechanistic processes underlying protein folding and dynamics are few since the target analytes-high-energy structural intermediates-are short lived and often difficult to distinguish from coexisting structures. Folding "intermediates" can be populated at equilibrium using weakly denaturing solvents, but it is not clear that these species are identical to those that are transiently populated during folding under "native" conditions. Oxidative labeling with mass spectrometric analysis is a powerful alternative for structural characterization of proteins and transient protein species based on solvent exposure at specific sites. RECENT ADVANCES Oxidative labeling is increasingly used with exceedingly short (μs) labeling pulses, both to minimize the occurrence of artifactual structural changes due to the incorporation of label and to detect short-lived species. The recent introduction of facile photolytic approaches for producing reactive oxygen species is an important technological advance that will enable more widespread adoption of the technique. CRITICAL ISSUES The most common critique of oxidative labeling data is that even with brief labeling pulses, covalent modification of the protein may cause significant artifactual structural changes. FUTURE DIRECTIONS While the oxidative labeling with the analysis by mass spectrometry is mature enough that most basic methodological issues have been addressed, a complete systematic understanding of side chain reactivity in the context of intact proteins is an avenue for future work. Specifically, there remain issues around the impact of primary sequence and side chain interactions on the reactivity of "solvent-exposed" residues. Due to its analytical power, wide range of applications, and relative ease of implementation, oxidative labeling is an increasingly important technique in the bioanalytical toolbox.
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Affiliation(s)
- Peter Liuni
- 1 Department of Chemistry, York University , Toronto, Canada
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21
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Zinck N, Stark AK, Wilson DJ, Sharon M. An improved rapid mixing device for time-resolved electrospray mass spectrometry measurements. ChemistryOpen 2014; 3:109-14. [PMID: 25050229 PMCID: PMC4101726 DOI: 10.1002/open.201402002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Indexed: 12/12/2022] Open
Abstract
Time series data can provide valuable insight into the complexity of biological reactions. Such information can be obtained by mass-spectrometry-based approaches that measure pre-steady-state kinetics. These methods are based on a mixing device that rapidly mixes the reactants prior to the on-line mass measurement of the transient intermediate steps. Here, we describe an improved continuous-flow mixing apparatus for real-time electrospray mass spectrometry measurements. Our setup was designed to minimize metal–solution interfaces and provide a sheath flow of nitrogen gas for generating stable and continuous spray that consequently enhances the signal-to-noise ratio. Moreover, the device was planned to enable easy mounting onto a mass spectrometer replacing the commercial electrospray ionization source. We demonstrate the performance of our apparatus by monitoring the unfolding reaction of cytochrome C, yielding improved signal-to-noise ratio and reduced experimental repeat errors.
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Affiliation(s)
- Nicholas Zinck
- Department of Chemistry, York University Toronto, ON M3J 1P3 (Canada)
| | - Ann-Kathrin Stark
- Department of Biological Chemistry, Weizmann Institute of Science 76100 Rehovot (Israel) E-mail:
| | - Derek J Wilson
- Department of Chemistry, York University Toronto, ON M3J 1P3 (Canada)
| | - Michal Sharon
- Department of Biological Chemistry, Weizmann Institute of Science 76100 Rehovot (Israel) E-mail:
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22
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Khanal A, Pan Y, Brown LS, Konermann L. Pulsed hydrogen/deuterium exchange mass spectrometry for time-resolved membrane protein folding studies. JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:1620-6. [PMID: 23280751 DOI: 10.1002/jms.3127] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 10/16/2012] [Accepted: 10/17/2012] [Indexed: 05/10/2023]
Abstract
Kinetic folding experiments by pulsed hydrogen/deuterium exchange (HDX) mass spectrometry (MS) are a well-established tool for water-soluble proteins. To the best of our knowledge, the current study is the first that applies this approach to an integral membrane protein. The native state of bacteriorhodopsin (BR) comprises seven transmembrane helices and a covalently bound retinal cofactor. BR exposure to sodium dodecyl sulfate (SDS) induces partial unfolding and retinal loss. We employ a custom-built three-stage mixing device for pulsed-HDX/MS investigations of BR refolding. The reaction is triggered by mixing SDS-denatured protein with bicelles. After a variable folding time (10 ms to 24 h), the protein is exposed to excess D(2) O buffer under rapid exchange conditions. The HDX pulse is terminated by acid quenching after 24 ms. Subsequent off-line analysis is performed by size exclusion chromatography and electrospray MS. These measurements yield the number of protected backbone N-H sites as a function of folding time, reflecting the recovery of secondary structure. Our results indicate that much of the BR secondary structure is formed quite late during the reaction, on a time scale of 10 s and beyond. It is hoped that in the future it will be possible to extend the pulsed-HDX/MS approach employed here to membrane proteins other than BR.
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Affiliation(s)
- Anil Khanal
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
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23
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Dürr UN, Gildenberg M, Ramamoorthy A. The magic of bicelles lights up membrane protein structure. Chem Rev 2012; 112:6054-74. [PMID: 22920148 PMCID: PMC3497859 DOI: 10.1021/cr300061w] [Citation(s) in RCA: 266] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Indexed: 12/12/2022]
Affiliation(s)
| | - Melissa Gildenberg
- Biophysics
and Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055,
United States
| | - Ayyalusamy Ramamoorthy
- Biophysics
and Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055,
United States
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24
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Pan Y, Ruan X, Valvano MA, Konermann L. Validation of membrane protein topology models by oxidative labeling and mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:889-898. [PMID: 22410873 DOI: 10.1007/s13361-012-0342-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Revised: 01/12/2012] [Accepted: 01/17/2012] [Indexed: 05/31/2023]
Abstract
Computer-assisted topology predictions are widely used to build low-resolution structural models of integral membrane proteins (IMPs). Experimental validation of these models by traditional methods is labor intensive and requires modifications that might alter the IMP native conformation. This work employs oxidative labeling coupled with mass spectrometry (MS) as a validation tool for computer-generated topology models. ·OH exposure introduces oxidative modifications in solvent-accessible regions, whereas buried segments (e.g., transmembrane helices) are non-oxidizable. The Escherichia coli protein WaaL (O-antigen ligase) is predicted to have 12 transmembrane helices and a large extramembrane domain (Pérez et al., Mol. Microbiol. 2008, 70, 1424). Tryptic digestion and LC-MS/MS were used to map the oxidative labeling behavior of WaaL. Met and Cys exhibit high intrinsic reactivities with ·OH, making them sensitive probes for solvent accessibility assays. Overall, the oxidation pattern of these residues is consistent with the originally proposed WaaL topology. One residue (M151), however, undergoes partial oxidation despite being predicted to reside within a transmembrane helix. Using an improved computer algorithm, a slightly modified topology model was generated that places M151 closer to the membrane interface. On the basis of the labeling data, it is concluded that the refined model more accurately reflects the actual topology of WaaL. We propose that the combination of oxidative labeling and MS represents a useful strategy for assessing the accuracy of IMP topology predictions, supplementing data obtained in traditional biochemical assays. In the future, it might be possible to incorporate oxidative labeling data directly as constraints in topology prediction algorithms.
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Affiliation(s)
- Yan Pan
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
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25
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Krishnamani V, Hegde BG, Langen R, Lanyi JK. Secondary and Tertiary Structure of Bacteriorhodopsin in the SDS Denatured State. Biochemistry 2012; 51:1051-60. [DOI: 10.1021/bi201769z] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Venkatramanan Krishnamani
- Department
of Physiology and Biophysics, University of California, Irvine, Irvine, California 92697, United States
| | - Balachandra G. Hegde
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California
90033, United States
| | - Ralf Langen
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California
90033, United States
| | - Janos K. Lanyi
- Department
of Physiology and Biophysics, University of California, Irvine, Irvine, California 92697, United States
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26
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Pan Y, Piyadasa H, O'Neil JD, Konermann L. Conformational dynamics of a membrane transport protein probed by H/D exchange and covalent labeling: the glycerol facilitator. J Mol Biol 2011; 416:400-13. [PMID: 22227391 DOI: 10.1016/j.jmb.2011.12.052] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Revised: 12/21/2011] [Accepted: 12/21/2011] [Indexed: 01/22/2023]
Abstract
Glycerol facilitator (GF) is a tetrameric membrane protein responsible for the selective permeation of glycerol and water. Each of the four GF subunits forms a transmembrane channel. Every subunit consists of six helices that completely span the lipid bilayer, as well as two half-helices (TM7 and TM3). X-ray crystallography has revealed that the selectivity of GF is due to its unique amphipathic channel interior. To explore the structural dynamics of GF, we employ hydrogen/deuterium exchange (HDX) and oxidative labeling with mass spectrometry (MS). HDX-MS reveals that transmembrane helices are generally more protected than extramembrane segments, consistent with data previously obtained for other membrane proteins. Interestingly, TM7 does not follow this trend. Instead, this half-helix undergoes rapid deuteration, indicative of a highly dynamic local structure. The oxidative labeling behavior of most GF residues is consistent with the static crystal structure. However, the side chains of C134 and M237 undergo labeling although they should be inaccessible according to the X-ray structure. In agreement with our HDX-MS data, this observation attests to the fact that TM7 is only marginally stable. We propose that the highly mobile nature of TM7 aids in the efficient diffusion of guest molecules through the channel ("molecular lubrication"). In the absence of such dynamics, host-guest molecular recognition would favor semipermanent binding of molecules inside the channel, thereby impeding transport. The current work highlights the complementary nature of HDX, covalent labeling, and X-ray crystallography for the characterization of membrane proteins.
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Affiliation(s)
- Yan Pan
- Department of Chemistry, The University of Western Ontario, London, ON, Canada N6A 5B7
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27
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Pan Y, Brown L, Konermann L. Hydrogen exchange mass spectrometry of bacteriorhodopsin reveals light-induced changes in the structural dynamics of a biomolecular machine. J Am Chem Soc 2011; 133:20237-44. [PMID: 22043856 DOI: 10.1021/ja206197h] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Many proteins act as molecular machines that are fuelled by a nonthermal energy source. Examples include transmembrane pumps and stator-rotor complexes. These systems undergo cyclic motions (CMs) that are being driven along a well-defined conformational trajectory. Superimposed on these CMs are thermal fluctuations (TFs) that are coupled to stochastic motions of the solvent. Here we explore whether the TFs of a molecular machine are affected by the occurrence of CMs. Bacteriorhodopsin (BR) is a light-driven proton pump that serves as a model system in this study. The function of BR is based on a photocycle that involves trans/cis isomerization of a retinal chromophore, as well as motions of transmembrane helices. Hydrogen/deuterium exchange (HDX) mass spectrometry was used to monitor the TFs of BR, focusing on the monomeric form of the protein. Comparative HDX studies were conducted under illumination and in the dark. The HDX kinetics of BR are dramatically accelerated in the presence of light. The isotope exchange rates and the number of backbone amides involved in EX2 opening transitions increase roughly 2-fold upon illumination. In contrast, light/dark control experiments on retinal-free protein produced no discernible differences. It can be concluded that the extent of TFs in BR strongly depends on photon-driven CMs. The light-induced differences in HDX behavior are ascribed to protein destabilization. Specifically, the thermodynamic stability of the dark-adapted protein is estimated to be 5.5 kJ mol(-1) under the conditions of our work. This value represents the free energy difference between the folded state F and a significantly unfolded conformer U. Illumination reduces the stability of F by 2.2 kJ mol(-1). Mechanical agitation caused by isomerization of the chromophore is transferred to the surrounding protein scaffold, and subsequently, the energy dissipates into the solvent. Light-induced retinal motions therefore act analogously to an internal heat source that promotes the occurrence of TFs. Overall, our data highlight the potential of HDX methods for probing the structural dynamics of molecular machines under "engine on" and "engine off" conditions.
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Affiliation(s)
- Yan Pan
- Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
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28
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Souda P, Ryan CM, Cramer WA, Whitelegge J. Profiling of integral membrane proteins and their post translational modifications using high-resolution mass spectrometry. Methods 2011; 55:330-6. [PMID: 21982782 DOI: 10.1016/j.ymeth.2011.09.019] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2011] [Revised: 09/18/2011] [Accepted: 09/21/2011] [Indexed: 11/28/2022] Open
Abstract
Integral membrane proteins pose challenges to traditional proteomics approaches due to unique physicochemical properties including hydrophobic transmembrane domains that limit solubility in aqueous solvents. A well resolved intact protein molecular mass profile defines a protein's native covalent state including post-translational modifications, and is thus a vital measurement toward full structure determination. Both soluble loop regions and transmembrane regions potentially contain post-translational modifications that must be characterized if the covalent primary structure of a membrane protein is to be defined. This goal has been achieved using electrospray-ionization mass spectrometry (ESI-MS) with low-resolution mass analyzers for intact protein profiling, and high-resolution instruments for top-down experiments, toward complete covalent primary structure information. In top-down, the intact protein profile is supplemented by gas-phase fragmentation of the intact protein, including its transmembrane regions, using collisionally activated and/or electron-capture dissociation (CAD/ECD) to yield sequence-dependent high-resolution MS information. Dedicated liquid chromatography systems with aqueous/organic solvent mixtures were developed allowing us to demonstrate that polytopic integral membrane proteins are amenable to ESI-MS analysis, including top-down measurements. Covalent post-translational modifications are localized regardless of their position in transmembrane domains. Top-down measurements provide a more detail oriented high-resolution description of post-transcriptional and post-translational diversity for enhanced understanding beyond genomic translation.
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Affiliation(s)
- Puneet Souda
- The Pasarow Mass Spectrometry Laboratory, NPI-Semel Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
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29
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Grossman M, Sela-Passwell N, Sagi I. Achieving broad molecular insights into dynamic protein interactions by integrated structural-kinetic approaches. Curr Opin Struct Biol 2011; 21:678-85. [PMID: 21945040 DOI: 10.1016/j.sbi.2011.07.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Revised: 07/21/2011] [Accepted: 07/31/2011] [Indexed: 11/30/2022]
Abstract
A network of dynamic protein interactions with their protein partners, substrates, and ligands is known to be crucial for biological function. Revealing molecular and structural-based mechanisms at atomic resolution and in real-time is fundamental for achieving a basic understanding of cellular processes. These technically challenging goals may be achieved by combining time-resolved spectroscopic and structural-kinetic tools, thus providing broad insights into specific molecular events over a wide range of timescales. Here we review representative studies utilizing such an integrated real-time structural approach designed to reveal molecular mechanisms underlying protein interactions at atomic resolution.
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Affiliation(s)
- Moran Grossman
- Departments of Structural Biology and Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel
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30
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Konermann L, Pan Y, Stocks BB. Protein folding mechanisms studied by pulsed oxidative labeling and mass spectrometry. Curr Opin Struct Biol 2011; 21:634-40. [PMID: 21703846 DOI: 10.1016/j.sbi.2011.05.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Revised: 05/21/2011] [Accepted: 05/26/2011] [Indexed: 12/14/2022]
Abstract
Deciphering the mechanisms of protein folding remains a considerable challenge. In this review we discuss the application of pulsed oxidative labeling for tracking protein structural changes in a time-resolved fashion. Exposure to a microsecond OH pulse at selected time points during folding induces the oxidation of solvent-accessible side chains, whereas buried residues are protected. Oxidative modifications can be detected by mass spectrometry. Folding is associated with dramatic accessibility changes, and therefore this method can provide detailed mechanistic insights. Solvent accessibility patterns are complementary to H/D exchange investigations, which report on the extent of hydrogen bonding. This review highlights the application of pulsed OH labeling to soluble proteins as well as membrane proteins.
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Affiliation(s)
- Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, ON N6A 5B7, Canada.
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