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Kaushik Rangadurai A, Toyama Y, Kay LE. Practical considerations for the measurement of near-surface electrostatics based on solvent paramagnetic relaxation enhancements. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 349:107400. [PMID: 36796143 DOI: 10.1016/j.jmr.2023.107400] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Revised: 02/02/2023] [Accepted: 02/03/2023] [Indexed: 06/18/2023]
Abstract
Electrostatic interactions can play important roles in regulating various biological processes. Quantifying surface electrostatics of biomolecules is, therefore, of significant interest. Recent advances in solution NMR spectroscopy have enabled site-specific measurements of de novo near-surface electrostatic potentials (ϕENS) based on a comparison of solvent paramagnetic relaxation enhancements generated from differently charged paramagnetic co-solutes with similar structures. Although the NMR-derived near-surface electrostatic potentials have been shown to agree with theoretical calculations in the context of folded proteins and nucleic acids, such benchmark comparisons may not always be possible, particularly in cases where high-resolution structural models are lacking, such as in the study of intrinsically disordered proteins. Cross-validation of ϕENS potentials can be achieved by comparing values obtained using three pairs of paramagnetic co-solutes, each with a different net charge. Notably we have found cases where agreement of ϕENS potentials between the three pairs is poor and herein we investigate the source of this discrepancy in some detail. We show that for the systems considered here ϕENS potentials obtained from cationic and anionic co-solutes are accurate and that the use of paramagnetic co-solutes with different structures can be a viable option for validation, although the optimal choice of paramagnetic compounds depends on the system of interest.
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Affiliation(s)
- Atul Kaushik Rangadurai
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Chemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Hospital for Sick Children, Program in Molecular Medicine, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada.
| | - Yuki Toyama
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Chemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
| | - Lewis E Kay
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Chemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Hospital for Sick Children, Program in Molecular Medicine, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada.
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Toyama Y, Rangadurai AK, Kay LE. Measurement of 1H α transverse relaxation rates in proteins: application to solvent PREs. JOURNAL OF BIOMOLECULAR NMR 2022; 76:137-152. [PMID: 36018482 DOI: 10.1007/s10858-022-00401-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 07/18/2022] [Indexed: 06/15/2023]
Abstract
It has recently been demonstrated that accurate near surface electrostatic potentials can be calculated for proteins from solvent paramagnetic relaxation enhancements (PREs) of amide protons measured using spin labels of similar structures but different charges (Yu et al. in Proc Natl Acad Sci 118(25):e2104020118, 2021). Here we develop methodology for extending such measurements to intrinsically disordered proteins at neutral pH where amide spectra are of very poor quality. Under these conditions it is shown that accurate PRE values can be measured using the haCONHA experiment that has been modified for recording 1Hα transverse relaxation rates. The optimal pulse scheme includes a spin-lock relaxation element for suppression of homonuclear scalar coupled evolution for all 1Hα protons, except those derived from Ser and Thr residues, and minimizes the radiation damping field from water magnetization that would otherwise increase measured relaxation rates. The robustness of the experiment is verified by developing a second approach using a band selective adiabatic decoupling scheme for suppression of scalar coupling modulations during 1Hα relaxation and showing that the measured PRE values from the two methods are in excellent agreement. The near surface electrostatic potential of a 103-residue construct comprising the C-terminal intrinsically disordered region of the RNA-binding protein CAPRIN1 is obtained at pH 5.5 using both 1HN and 1Hα-based relaxation rates, and at pH 7.4 where only 1Hα rates can be quantified, with very good agreement between potentials obtained under all experimental conditions.
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Affiliation(s)
- Yuki Toyama
- Department of Molecular Genetics, University of Toronto, Toronto, M5S 1A8, Canada.
- Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada.
- Department of Biochemistry, University of Toronto, Toronto, ON, M5S 1A8, Canada.
| | - Atul Kaushik Rangadurai
- Department of Molecular Genetics, University of Toronto, Toronto, M5S 1A8, Canada
- Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, M5S 1A8, Canada
- Program in Molecular Medicine, Hospital for Sick Children Research Institute, Toronto, ON, M5G 0A4, Canada
| | - Lewis E Kay
- Department of Molecular Genetics, University of Toronto, Toronto, M5S 1A8, Canada.
- Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada.
- Department of Biochemistry, University of Toronto, Toronto, ON, M5S 1A8, Canada.
- Program in Molecular Medicine, Hospital for Sick Children Research Institute, Toronto, ON, M5G 0A4, Canada.
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Zaiss M, Angelovski G, Demetriou E, McMahon MT, Golay X, Scheffler K. QUESP and QUEST revisited - fast and accurate quantitative CEST experiments. Magn Reson Med 2017; 79:1708-1721. [PMID: 28686796 DOI: 10.1002/mrm.26813] [Citation(s) in RCA: 76] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 05/17/2017] [Accepted: 06/03/2017] [Indexed: 01/24/2023]
Abstract
PURPOSE Chemical exchange saturation transfer (CEST) NMR or MRI experiments allow detection of low concentrated molecules with enhanced sensitivity via their proton exchange with the abundant water pool. Be it endogenous metabolites or exogenous contrast agents, an exact quantification of the actual exchange rate is required to design optimal pulse sequences and/or specific sensitive agents. METHODS Refined analytical expressions allow deeper insight and improvement of accuracy for common quantification techniques. The accuracy of standard quantification methodologies, such as quantification of exchange rate using varying saturation power or varying saturation time, is improved especially for the case of nonequilibrium initial conditions and weak labeling conditions, meaning the saturation amplitude is smaller than the exchange rate (γB1 < k). RESULTS The improved analytical 'quantification of exchange rate using varying saturation power/time' (QUESP/QUEST) equations allow for more accurate exchange rate determination, and provide clear insights on the general principles to execute the experiments and to perform numerical evaluation. The proposed methodology was evaluated on the large-shift regime of paramagnetic chemical-exchange-saturation-transfer agents using simulated data and data of the paramagnetic Eu(III) complex of DOTA-tetraglycineamide. CONCLUSIONS The refined formulas yield improved exchange rate estimation. General convergence intervals of the methods that would apply for smaller shift agents are also discussed. Magn Reson Med 79:1708-1721, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Moritz Zaiss
- High Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Goran Angelovski
- MR Neuroimaging Agents, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Eleni Demetriou
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom
| | - Michael T McMahon
- Division of MR Research, The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, USA
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA
| | - Xavier Golay
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom
| | - Klaus Scheffler
- High Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
- Department of Biomedical Magnetic Resonance, Eberhard Karl's University of Tübingen and University Hospital, Tübingen, Germany
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Chao FA, Byrd RA. Application of geometric approximation to the CPMG experiment: Two- and three-site exchange. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 277:8-14. [PMID: 28189995 PMCID: PMC5405725 DOI: 10.1016/j.jmr.2017.01.022] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 01/26/2017] [Accepted: 01/29/2017] [Indexed: 06/06/2023]
Abstract
The Carr-Purcell-Meiboom-Gill (CPMG) experiment is one of the most classical and well-known relaxation dispersion experiments in NMR spectroscopy, and it has been successfully applied to characterize biologically relevant conformational dynamics in many cases. Although the data analysis of the CPMG experiment for the 2-site exchange model can be facilitated by analytical solutions, the data analysis in a more complex exchange model generally requires computationally-intensive numerical analysis. Recently, a powerful computational strategy, geometric approximation, has been proposed to provide approximate numerical solutions for the adiabatic relaxation dispersion experiments where analytical solutions are neither available nor feasible. Here, we demonstrate the general potential of geometric approximation by providing a data analysis solution of the CPMG experiment for both the traditional 2-site model and a linear 3-site exchange model. The approximate numerical solution deviates less than 0.5% from the numerical solution on average, and the new approach is computationally 60,000-fold more efficient than the numerical approach. Moreover, we find that accurate dynamic parameters can be determined in most cases, and, for a range of experimental conditions, the relaxation can be assumed to follow mono-exponential decay. The method is general and applicable to any CPMG RD experiment (e.g. N, C', Cα, Hα, etc.) The approach forms a foundation of building solution surfaces to analyze the CPMG experiment for different models of 3-site exchange. Thus, the geometric approximation is a general strategy to analyze relaxation dispersion data in any system (biological or chemical) if the appropriate library can be built in a physically meaningful domain.
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Affiliation(s)
- Fa-An Chao
- Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA
| | - R Andrew Byrd
- Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA.
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