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Kish M, Subramanian S, Smith V, Lethbridge N, Cole L, Vollmer F, Bond NJ, Phillips JJ. Allosteric Regulation of Glycogen Phosphorylase by Order/Disorder Transition of the 250' and 280s Loops. Biochemistry 2023; 62:1360-1368. [PMID: 36989206 PMCID: PMC10116597 DOI: 10.1021/acs.biochem.2c00671] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
Allostery is a fundamental mechanism of protein activation, yet the precise dynamic changes that underlie functional regulation of allosteric enzymes, such as glycogen phosphorylase (GlyP), remain poorly understood. Despite being the first allosteric enzyme described, its structural regulation is still a challenging problem: the key regulatory loops of the GlyP active site (250' and 280s) are weakly stable and often missing density or have large b-factors in structural models. This led to the longstanding hypothesis that GlyP regulation is achieved through gating of the active site by (dis)order transitions, as first proposed by Barford and Johnson. However, testing this requires a quantitative measurement of weakly stable local structure which, to date, has been technically challenging in such a large protein. Hydrogen-deuterium-exchange mass spectrometry (HDX-MS) is a powerful tool for studying protein dynamics, and millisecond HDX-MS has the ability to measure site-localized stability differences in weakly stable structures, making it particularly valuable for investigating allosteric regulation in GlyP. Here, we used millisecond HDX-MS to measure the local structural perturbations of glycogen phosphorylase b (GlyPb), the phosphorylated active form (GlyPa), and the inhibited glucose-6 phosphate complex (GlyPb:G6P) at near-amino acid resolution. Our results support the Barford and Johnson hypothesis for GlyP regulation by providing insight into the dynamic changes of the key regulatory loops.
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Affiliation(s)
- Monika Kish
- Living Systems Institute, Department of Biosciences, University of Exeter, Stocker Road, Exeter, EX4 4QD, U.K
| | - Sivaraman Subramanian
- Living Systems Institute, Department of Physics, University of Exeter, Stocker Road, Exeter, EX4 6QD, U.K
| | | | | | - Lindsay Cole
- Applied Photophysics Ltd, Leatherhead, KT227BA, U.K
| | - Frank Vollmer
- Living Systems Institute, Department of Physics, University of Exeter, Stocker Road, Exeter, EX4 6QD, U.K
| | - Nicholas J Bond
- Analytical Sciences, Biopharmaceutical Development, BioPharmaceuticals R&D, AstraZeneca, Milstein Building, Granta Park, Cambridge, CB21 6GH, U.K
| | - Jonathan J Phillips
- Living Systems Institute, Department of Biosciences, University of Exeter, Stocker Road, Exeter, EX4 4QD, U.K
- Alan Turing Institute, British Library, London, NW1 2DB, U.K
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2
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Kish M, Smith V, Lethbridge N, Cole L, Bond NJ, Phillips JJ. Online Fully Automated System for Hydrogen/Deuterium-Exchange Mass Spectrometry with Millisecond Time Resolution. Anal Chem 2023; 95:5000-5008. [PMID: 36896500 PMCID: PMC10034745 DOI: 10.1021/acs.analchem.2c05310] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/11/2023]
Abstract
Amide hydrogen/deuterium-exchange mass spectrometry (HDX-MS) is a powerful tool for analyzing the conformational dynamics of proteins in a solution. Current conventional methods have a measurement limit starting from several seconds and are solely reliant on the speed of manual pipetting or a liquid handling robot. Weakly protected regions of polypeptides, such as in short peptides, exposed loops and intrinsically disordered the protein exchange on the millisecond timescale. Typical HDX methods often cannot resolve the structural dynamics and stability in these cases. Numerous academic laboratories have demonstrated the considerable utility of acquiring HDX-MS data in the sub-second regimes. Here, we describe the development of a fully automated HDX-MS apparatus to resolve amide exchange on the millisecond timescale. Like conventional systems, this instrument boasts automated sample injection with software selection of labeling times, online flow mixing and quenching, while being fully integrated with a liquid chromatography-MS system for existing standard "bottom-up" workflows. HDX-MS's rapid exchange kinetics of several peptides demonstrate the repeatability, reproducibility, back-exchange, and mixing kinetics achieved with the system. Comparably, peptide coverage of 96.4% with 273 peptides was achieved, supporting the equivalence of the system to standard robotics. Additionally, time windows of 50 ms-300 s allowed full kinetic transitions to be observed for many amide groups; especially important are short time points (50-150 ms) for regions that are likely highly dynamic and solvent- exposed. We demonstrate that information on structural dynamics and stability can be measured for stretches of weakly stable polypeptides in small peptides and in local regions of a large enzyme, glycogen phosphorylase.
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Affiliation(s)
- Monika Kish
- Living Systems Institute, Department of Biosciences, University of Exeter, Stocker Road, Exeter, EX4 4QD, U.K
| | | | | | - Lindsay Cole
- Applied Photophysics Ltd, Leatherhead KT227BA, U.K
| | - Nicholas J Bond
- Analytical Sciences, Biopharmaceutical Development, BioPharmaceuticals R&D, AstraZeneca, Milstein Building, Granta Park, Cambridge CB21 6GH, U.K
| | - Jonathan J Phillips
- Living Systems Institute, Department of Biosciences, University of Exeter, Stocker Road, Exeter, EX4 4QD, U.K
- Alan Turing Institute, British Library, London NW1 2DB, U.K
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3
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Cain RL, Webb IK. Online protein unfolding characterized by ion mobility electron capture dissociation mass spectrometry: cytochrome C from neutral and acidic solutions. Anal Bioanal Chem 2023; 415:749-758. [PMID: 36622393 DOI: 10.1007/s00216-022-04501-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2022] [Revised: 12/02/2022] [Accepted: 12/20/2022] [Indexed: 01/10/2023]
Abstract
Electrospray ionization mass spectrometry (ESI-MS) experiments, including ion mobility spectrometry mass spectrometry (ESI-IMS-MS) and electron capture dissociation (ECD) of proteins ionized from aqueous solutions, have been used for the study of solution-like structures of intact proteins. By mixing aqueous proteins with denaturants online before ESI, the amount of protein unfolding can be precisely controlled and rapidly analyzed, permitting the characterization of protein folding intermediates in protein folding pathways. Herein, we mixed various pH solutions online with aqueous cytochrome C for unfolding and characterizing its unfolding intermediates with ESI-MS charge state distribution measurements, IMS, and ECD. The presence of folding intermediates and unfolded cytochrome c structures were detected from changes in charge states, arrival time distributions (ATDs), and ECD. We also compared structures from nondenaturing and denaturing solution mixtures measured under "gentle" (i.e., low energy) ion transmission conditions with structures measured under "harsh" (i.e., higher energy) transmission. This work confirms that when using "gentle" instrument conditions, the gas-phase cytochrome c ions reflect attributes of the various solution-phase structures. However, "harsh" conditions that maximize ion transmission produce extended structures that no longer correlate with changes in solution structure.
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Affiliation(s)
- Rebecca L Cain
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN, 46202, USA
| | - Ian K Webb
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN, 46202, USA.
- Center for Computational Biology and Bioinformatics, Indiana University School of Medicine, Indianapolis, IN, 46202, USA.
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4
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Li W, Chaihu L, Jiang J, Wu B, Zheng X, Dai R, Tian Y, Huang Y, Wang G, Men Y. Microfluidic Platform for Time-Resolved Characterization of Protein Higher-Order Structures and Dynamics Using Top-Down Mass Spectrometry. Anal Chem 2022; 94:7520-7527. [PMID: 35584038 DOI: 10.1021/acs.analchem.2c00077] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Characterization of protein higher-order structures and dynamics is essential for understanding the biological functions of proteins and revealing the underlying mechanisms. Top-down mass spectrometry (MS) accesses structural information at both the intact protein level and the peptide fragment level. Native top-down MS allows analysis of a protein complex's architecture and subunits' identity and modifications. Top-down hydrogen/deuterium exchange (HDX) MS offers high spatial resolution for conformational or binding interface analysis and enables conformer-specific characterization. A microfluidic chip can provide superior performance for front-end reactions useful for these MS workflows, such as flexibility in manipulating multiple reactant flows, integrating various functional modules, and automation. However, most microchip-MS devices are designed for bottom-up approaches or top-down proteomics. Here, we demonstrate a strategy for designing a microchip for top-down MS analysis of protein higher-order structures and dynamics. It is suitable for time-resolved native MS and HDX MS, with designs aiming for efficient ionization of intact protein complexes, flexible manipulation of multiple reactant flows, and precise control of reaction times over a broad range of flow rates on the submicroliter per minute scale. The performance of the prototype device is demonstrated by measurements of systems including monoclonal antibodies, antibody-antigen complexes, and coexisting protein conformers. This strategy may benefit elaborate structural analysis of biomacromolecules and inspire method development using the microchip-MS approach.
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Affiliation(s)
- Wen Li
- Research Center for Biomedical Optics and Molecular Imaging, Institute of Biomedical and Health Engineering, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Lingxiao Chaihu
- School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China.,Institute of Cell Analysis, Shenzhen Bay Laboratory, Shenzhen 518132, China
| | - Jialu Jiang
- School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China
| | - Bizhu Wu
- Research Center for Biomedical Optics and Molecular Imaging, Institute of Biomedical and Health Engineering, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Xuan Zheng
- Research Center for Biomedical Optics and Molecular Imaging, Institute of Biomedical and Health Engineering, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Rongrong Dai
- School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China
| | - Ye Tian
- Institute of Cell Analysis, Shenzhen Bay Laboratory, Shenzhen 518132, China
| | - Yanyi Huang
- Institute of Cell Analysis, Shenzhen Bay Laboratory, Shenzhen 518132, China.,Biomedical Pioneering Innovation Centre, Peking University, Beijing 100871, China
| | - Guanbo Wang
- Institute of Cell Analysis, Shenzhen Bay Laboratory, Shenzhen 518132, China.,Biomedical Pioneering Innovation Centre, Peking University, Beijing 100871, China
| | - Yongfan Men
- Research Center for Biomedical Optics and Molecular Imaging, Institute of Biomedical and Health Engineering, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
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5
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Corona discharge electrospray ionization of formate-containing solutions enables in-source reduction of disulfide bonds. Anal Bioanal Chem 2018; 411:4729-4737. [PMID: 30397758 DOI: 10.1007/s00216-018-1447-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 10/12/2018] [Accepted: 10/22/2018] [Indexed: 01/05/2023]
Abstract
Disulfide bonds are critical linkages for maintaining protein structure and enzyme activity. These linkages, however, can limit peptide sequencing efforts by mass spectrometry (MS) and often require chemical reduction and alkylation. Under such conditions, information regarding cysteine connectivity is lost. Online partial disulfide reduction within the electrospray (ESI) source has recently been established as a means to identify complex cysteine linkage patterns in a liquid chromatography-MS experiment without the need for sample pre-treatment. Corona discharge (CD) is invoked as the causative factor of this in-source reduction (ISR); however, evidence remains largely circumstantial. In this study, we demonstrate that instrumental factors-nebulizing gas, ESI capillary material, organic solvent content, ESI spray needle-to-MS distance-all modulate the degree of reduction observed for the single disulfide in oxytocin, further implicating CD in ISR. Rigorous analysis of solution conditions, however, reveals that corona discharge alone can induce only minor disulfide reduction. We establish that CD-ESI of peptide solutions containing formic acid or its conjugate base results in a dramatic increase in disulfide reduction. It is also determined that ISR is exacerbated at low pH for complex peptides containing multiple disulfide bonds and possessing higher-order structure, as well as for a small protein. Overall, our results demonstrate that ESI of formate/formic acid-containing solutions under corona discharge conditions facilitates disulfide ISR, likely by a similar reduction pathway measured in γ-radiolysis studies nearly three decades ago.
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6
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Stocks BB, Melanson JE. In-Source Reduction of Disulfide-Bonded Peptides Monitored by Ion Mobility Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:742-751. [PMID: 29450858 DOI: 10.1007/s13361-018-1894-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Revised: 01/15/2018] [Accepted: 01/18/2018] [Indexed: 06/08/2023]
Abstract
Many peptides with antimicrobial activity and/or therapeutic potential contain disulfide bonds as a means to enhance stability, and their quantitation is often performed using electrospray ionization mass spectrometry (ESI-MS). Disulfides can be reduced during ESI under commonly used instrument conditions, which has the potential to hinder accurate peptide quantitation. We demonstrate that this in-source reduction (ISR) is predominantly observed for peptides infused from acidic solutions and subjected to elevated ESI voltages (3-4 kV). ISR is readily apparent in the mass spectrum of oxytocin-a small, single disulfide-containing peptide. However, subtle m/z shifts due to partial ISR of highly charged (z ≥ 3) peptides with multiple disulfide linkages may proceed unnoticed. Ion mobility (IM)-MS separates ions on the basis of charge and shape in the gas phase, and using insulin as a model system, we show that IM-MS arrival time distributions (ATDs) are particularly sensitive to partial ISR of large peptides. Isotope modeling allows for the relative quantitation of disulfide-intact and partially reduced states of the mobility-separated peptide conformers. Interestingly, hepcidin peptides ionized from acidic solutions at elevated ESI voltages undergo gas-phase compaction, ostensibly due to partial disulfide ISR. Our IM-MS results lead us to propose that residual acid is the likely cause of disparate ATDs recently measured for hepcidin from different suppliers [Anal. Bioanal. Chem. 409, 2559-2567 (2017)]. Overall, our results demonstrate the utility of IM-MS to detect partial ISR of disulfide-bonded peptides and reinforce the notion that peptide/protein measurements should be carried out using minimally activating instrument conditions. Graphical Abstract ᅟ.
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Affiliation(s)
- Bradley B Stocks
- National Research Council of Canada, Measurement Science and Standards, 1200 Montreal Road, Ottawa, ON, K1A 0R6, Canada.
| | - Jeremy E Melanson
- National Research Council of Canada, Measurement Science and Standards, 1200 Montreal Road, Ottawa, ON, K1A 0R6, Canada
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7
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Patrick JW, Zerfas B, Gao J, Russell DH. Rapid capillary mixing experiments for the analysis of hydrophobic membrane complexes directly from aqueous lipid bilayer solutions. Analyst 2017; 142:310-315. [DOI: 10.1039/c6an02290a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Mixing tee-electrospray ionization coupled to ion mobility-mass spectrometry reveals gramicidin A dimer conformer preferences.
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Affiliation(s)
- John W. Patrick
- Department of Chemistry
- Texas A&M University
- College Station
- USA
| | | | - Jianmin Gao
- Department of Chemistry
- Boston College
- Chestnut Hill
- USA
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8
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Cong Y, Katipamula S, Trader CD, Orton DJ, Geng T, Baker ES, Kelly RT. Mass spectrometry-based monitoring of millisecond protein-ligand binding dynamics using an automated microfluidic platform. LAB ON A CHIP 2016; 16:1544-8. [PMID: 27009517 PMCID: PMC4846533 DOI: 10.1039/c6lc00183a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Characterizing protein-ligand binding dynamics is crucial for understanding protein function and for developing new therapeutic agents. We present a novel microfluidic platform that features rapid mixing of protein and ligand solutions, variable incubation times, and an integrated electrospray ionization source for mass spectrometry-based monitoring of protein-ligand binding dynamics. This platform offers many advantages, including solution-based binding, label-free detection, automated operation, rapid mixing, and low sample consumption.
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Affiliation(s)
- Yongzheng Cong
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
| | - Shanta Katipamula
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
| | - Cameron D Trader
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
| | - Daniel J Orton
- Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Tao Geng
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
| | - Erin S Baker
- Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Ryan T Kelly
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
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9
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Mortensen DN, Williams ER. Ultrafast (1 μs) Mixing and Fast Protein Folding in Nanodrops Monitored by Mass Spectrometry. J Am Chem Soc 2016; 138:3453-60. [PMID: 26902747 DOI: 10.1021/jacs.5b13081] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The use of theta-glass emitters and mass spectrometry to monitor reactions that occur as fast as one μs is demonstrated. Acidified aqueous solutions containing unfolded proteins are mixed with aqueous ammonium acetate solutions to increase the solution pH and induce protein folding during nanoelectrospray ionization. Protein charge-state distributions show the extent to which folding occurs, and reaction times are obtained from known protein folding time constants. Shorter reaction times are obtained by decreasing the solution flow rate, and reaction times between 1.0 and 22 μs are obtained using flow rates between 48 and 2880 pL/s, respectively. Remarkably similar reaction times are obtained for three different proteins (Trp-cage, myoglobin, and cytochrome c) with folding time constants that differ by more than an order of magnitude (4.1, 7, and 57 μs, respectively), indicating that the reaction times obtained using rapid mixing from theta-glass emitters are independent of protein identity. A folding time constant of 2.2 μs is obtained for the formation of a β-hairpin structure of renin substrate tetradecapeptide, which is the fastest folding event measured using a rapid mixing technique. The 1.0 μs reaction time obtained here is about an order of magnitude lower than the shortest reaction time probed using a conventional mixer (8 μs). Moreover, this fast reaction time is obtained with a 48 pL/s flow rate, which is 2000-times less than the flow rate required to obtained the 8 μs reaction time using a conventional mixer. These results indicate that rapid mixing with theta-glass emitters can be used to access significantly faster reaction times while consuming substantially less sample than in conventional mixing apparatus.
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Affiliation(s)
- Daniel N Mortensen
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
| | - Evan R Williams
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
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10
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Lento C, Audette GF, Wilson DJ. Time-resolved electrospray mass spectrometry — a brief history. CAN J CHEM 2015. [DOI: 10.1139/cjc-2014-0260] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
This review describes the evolution of time-resolved electrospray ionization mass spectrometry (TRESI-MS), a technology that was developed in large part at Western University. TRESI-MS was initially designed to characterize rapid chemical and biochemical reactions occurring on the millisecond time scale without need for a chromophore. Early TRESI-MS setups usually consisted of continuous-flow rapid mixers with a fixed tee for analysis of a single time point, and later adjustable reaction chamber devices allowing for automatic tracking of the reaction over time. Advances in instrumentation design over the years have resulted in improved time resolution, with microfluidic device implementation allowing for coupling to hydrogen−deuterium exchange (HDX) experiments. Areas of application that will be discussed include the investigation of protein folding intermediates, identification of enzyme−substrate intermediates in the pre-steady state, and the use of time-resolved HDX to study the dynamics of weakly structured protein regions. While some limitations still persist with the method, the continued development of TRESI-MS and related approaches paves the way to a promising future and the study of unexplored application areas.
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Affiliation(s)
- Cristina Lento
- Department of Chemistry, York University, Toronto, ON M3J 1P3, Canada
| | - Gerald F. Audette
- Department of Chemistry, York University, Toronto, ON M3J 1P3, Canada
- Center for Research on Biomolecular Interactions, Department of Chemistry, York University, Toronto, ON M3J 1P3, Canada
| | - Derek J. Wilson
- Department of Chemistry, York University, Toronto, ON M3J 1P3, Canada
- Center for Research on Biomolecular Interactions, Department of Chemistry, York University, Toronto, ON M3J 1P3, Canada
- Center for Research in Mass Spectrometry, Department of Chemistry, York University, Toronto, ON, M3J 1P3, Canada
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Mortensen DN, Williams ER. Investigating protein folding and unfolding in electrospray nanodrops upon rapid mixing using theta-glass emitters. Anal Chem 2014; 87:1281-7. [PMID: 25525976 PMCID: PMC4303338 DOI: 10.1021/ac503981c] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
Theta-glass emitters are used to
rapidly mix two solutions to induce
either protein folding or unfolding during nanoelectrospray (nanoESI).
Mixing acid-denatured myoglobin with an aqueous ammonium acetate solution
to increase solution pH results in protein folding during nanoESI.
A reaction time and upper limit to the droplet lifetime of 9 ±
2 μs is obtained from the relative abundance of the folded conformer
in these rapid mixing experiments compared to that obtained from solutions
at equilibrium and a folding time constant of 7 μs. Heme reincorporation
does not occur, consistent with the short droplet lifetime and the
much longer time constant for this process. Similar mixing experiments
with acid-denatured cytochrome c and the resulting
folding during nanoESI indicate a reaction time of between 7 and 25
μs depending on the solution composition. The extent of unfolding
of holo-myoglobin upon rapid mixing with theta-glass emitters is less
than that reported previously (Fisher
et al. Anal. Chem.2014, 86, 4581−458824702054), a result
that is attributed to the much smaller, ∼1.5 μm, average
o.d. tips used here. These results indicate that the time frame during
which protein folding or unfolding can occur during nanoESI depends
both on the initial droplet size, which can be varied by changing
the emitter tip diameter, and on the solution composition. This study
demonstrates that protein folding or unfolding processes that occur
on the ∼10 μs time scale can be readily investigated
using rapid mixing with theta-glass emitters combined with mass spectrometry.
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Affiliation(s)
- Daniel N Mortensen
- Department of Chemistry, University of California , Berkeley, California 94720-1460, United States
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