1
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Feng RR, Wang M, Zhang W, Gai F. Unnatural Amino Acids for Biological Spectroscopy and Microscopy. Chem Rev 2024; 124:6501-6542. [PMID: 38722769 DOI: 10.1021/acs.chemrev.3c00944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/23/2024]
Abstract
Due to advances in methods for site-specific incorporation of unnatural amino acids (UAAs) into proteins, a large number of UAAs with tailored chemical and/or physical properties have been developed and used in a wide array of biological applications. In particular, UAAs with specific spectroscopic characteristics can be used as external reporters to produce additional signals, hence increasing the information content obtainable in protein spectroscopic and/or imaging measurements. In this Review, we summarize the progress in the past two decades in the development of such UAAs and their applications in biological spectroscopy and microscopy, with a focus on UAAs that can be used as site-specific vibrational, fluorescence, electron paramagnetic resonance (EPR), or nuclear magnetic resonance (NMR) probes. Wherever applicable, we also discuss future directions.
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Affiliation(s)
- Ran-Ran Feng
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Manxi Wang
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Wenkai Zhang
- Department of Physics and Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875, China
| | - Feng Gai
- Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
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2
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Qianzhu H, Abdelkader EH, Otting G, Huber T. Genetic Encoding of Fluoro-l-tryptophans for Site-Specific Detection of Conformational Heterogeneity in Proteins by NMR Spectroscopy. J Am Chem Soc 2024; 146:13641-13650. [PMID: 38687675 DOI: 10.1021/jacs.4c03743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2024]
Abstract
The substitution of a single hydrogen atom in a protein by fluorine yields a site-specific probe for sensitive detection by 19F nuclear magnetic resonance (NMR) spectroscopy, where the absence of background signal from the protein facilitates the detection of minor conformational species. We developed genetic encoding systems for the site-selective incorporation of 4-fluorotryptophan, 5-fluorotryptophan, 6-fluorotryptophan, and 7-fluorotryptophan in response to an amber stop codon and used them to investigate conformational heterogeneity in a designed amino acid binding protein and in flaviviral NS2B-NS3 proteases. These proteases have been shown to present variable conformations in X-ray crystal structures, including flips of the indole side chains of tryptophan residues. The 19F NMR spectra of different fluorotryptophan isomers installed at the conserved site of Trp83 indicate that the indole ring flip is common in flaviviral NS2B-NS3 proteases in the apo state and suppressed by an active-site inhibitor.
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Affiliation(s)
- Haocheng Qianzhu
- Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
| | - Elwy H Abdelkader
- ARC Centre of Excellence for Innovations in Peptide & Protein Science, Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
| | - Gottfried Otting
- ARC Centre of Excellence for Innovations in Peptide & Protein Science, Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
| | - Thomas Huber
- Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
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3
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Liu J, Liu X, Zhang F, Qu J, Sun H, Zhu Q. A Peptide Stapling Strategy with Built‐In Fluorescence by Direct Late‐Stage C(sp
2
)−H Olefination of Tryptophan. Chemistry 2020; 26:16122-16128. [DOI: 10.1002/chem.202003548] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 08/27/2020] [Indexed: 12/31/2022]
Affiliation(s)
- Jiang Liu
- Key Laboratory of Bioorganic Synthesis of Zhejiang Province College of Biotechnology and Bioengineering Zhejiang University of Technology Hangzhou 310014 P.R. China
| | - Xin Liu
- Key Laboratory of Bioorganic Synthesis of Zhejiang Province College of Biotechnology and Bioengineering Zhejiang University of Technology Hangzhou 310014 P.R. China
| | - Fangfang Zhang
- Key Laboratory of Bioorganic Synthesis of Zhejiang Province College of Biotechnology and Bioengineering Zhejiang University of Technology Hangzhou 310014 P.R. China
| | - Jiaojiao Qu
- Key Laboratory of Bioorganic Synthesis of Zhejiang Province College of Biotechnology and Bioengineering Zhejiang University of Technology Hangzhou 310014 P.R. China
| | - Hongyan Sun
- Department of Chemistry and Center of Super-Diamond and Advanced Films (COSDAF) City University of Hong Kong Hong Kong P.R. China
| | - Qing Zhu
- Key Laboratory of Bioorganic Synthesis of Zhejiang Province College of Biotechnology and Bioengineering Zhejiang University of Technology Hangzhou 310014 P.R. China
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4
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Ampaw A, Carroll M, von Velsen J, Bhattasali D, Cohen A, Bowler MW, Jakeman DL. Observing enzyme ternary transition state analogue complexes by 19F NMR spectroscopy. Chem Sci 2017; 8:8427-8434. [PMID: 29619190 PMCID: PMC5863612 DOI: 10.1039/c7sc04204c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 10/23/2017] [Indexed: 11/21/2022] Open
Abstract
Ternary transition state analogue (TSA) complexes probing the isomerization of β-d-glucose 1-phosphate (G1P) into d-glucose 6-phosphate (G6P) catalyzed by catalytically active, fluorinated (5-fluorotryptophan), β-phosphoglucomutase (βPGM) have been observed directly by 19F NMR spectroscopy. In these complexes MgF3- and AlF4- are surrogates for the transferring phosphate. However, the relevance of these metal fluorides as TSA complexes has been queried. The 1D 19F spectrum of a ternary TSA complex presented a molar equivalence between fluorinated enzyme, metal fluoride and non-isomerizable fluoromethylenephosphonate substrate analogue. Ring flips of the 5-fluoroindole ring remote from the active site were observed by both 19F NMR and X-ray crystallography, but did not perturb function. This data unequivocally demonstrates that the concentration of the metal fluoride complexes is equivalent to the concentration of enzyme and ligand in the TSA complex in aqueous solution.
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Affiliation(s)
- Anna Ampaw
- Department of Chemistry , Dalhousie University , Halifax , NS , Canada B3H 4R2 .
| | - Madison Carroll
- Department of Chemistry , Dalhousie University , Halifax , NS , Canada B3H 4R2 .
| | - Jill von Velsen
- European Molecular Biology Laboratory , Grenoble Outstation , 71 avenue des Martyrs , CS 90181 F-38042 Grenoble , France
| | | | - Alejandro Cohen
- Proteomics and Mass Spectrometry Core Facility , Life Sciences Research Institute , Dalhousie University , Halifax , NS , Canada B3H 4R2
| | - Matthew W Bowler
- European Molecular Biology Laboratory , Grenoble Outstation , 71 avenue des Martyrs , CS 90181 F-38042 Grenoble , France
| | - David L Jakeman
- Department of Chemistry , Dalhousie University , Halifax , NS , Canada B3H 4R2 .
- College of Pharmacy , Dalhousie University , Halifax , NS , Canada B3H 4R2
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5
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Sun X, Dyson HJ, Wright PE. Fluorotryptophan Incorporation Modulates the Structure and Stability of Transthyretin in a Site-Specific Manner. Biochemistry 2017; 56:5570-5581. [PMID: 28920433 DOI: 10.1021/acs.biochem.7b00815] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Abnormal deposition of aggregated wild-type (WT) human transthyretin (TTR) and its pathogenic variants is responsible for cardiomyopathy and neuropathy related to TTR amyloidosis. The tryptophan (Trp) fluorescence measurements typically used to study structural changes of TTR do not yield site-specific information on the two Trp residues per TTR protomer. To obtain such information, tryptophan labeled with fluorine at the 5 and 6 positions (5FW and 6FW) was incorporated into TTR. Fluorescence of 5FW and 6FW-labeled WT-TTR (WT-5FW and WT-6FW) and a single-Trp mutant W41Y showed that the photophysics of incorporated fluoro-Trp is consistent with site-specific solvation of the indole ring of W41 and W79. 19F-NMR showed that solvent accessibility depends on both the location of the Trp and the position of the fluorine substituent in the indole ring. Unexpectedly, differences were observed in the rates of aggregation, with WT-6FW aggregating more rapidly than WT-5FW or WT-TTR. Real-time 19F-NMR urea unfolding experiments revealed that WT-5FW is kinetically more stable than WT-6FW, consistent with the aggregation assay. In addition, structural perturbations of residues distant from either Trp site are more extensive in WT-6FW. Notably, residues in the dimer interfaces are perturbed by 6FW at residue 79; pathogenic mutations in these regions are associated with reduced tetramer stability and amyloidogenesis. The differences in behavior that arise from the replacement of a fluorine at the 5-position of a tryptophan with one at the adjacent 6-position emphasize the delicate balance of stability in the TTR tetramer.
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Affiliation(s)
- Xun Sun
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - H Jane Dyson
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Peter E Wright
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
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6
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Xu J, Chen B, Callis P, Muiño PL, Rozeboom H, Broos J, Toptygin D, Brand L, Knutson JR. Picosecond fluorescence dynamics of tryptophan and 5-fluorotryptophan in monellin: slow water-protein relaxation unmasked. J Phys Chem B 2015; 119:4230-9. [PMID: 25710196 PMCID: PMC7477844 DOI: 10.1021/acs.jpcb.5b01651] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Time dependent fluorescence Stokes (emission wavelength) shifts (TDFSS) from tryptophan (Trp) following sub-picosecond excitation are increasingly used to investigate protein dynamics, most recently enabling active research interest into water dynamics near the surface of proteins. Unlike many fluorescence probes, both the efficiency and the wavelength of Trp fluorescence in proteins are highly sensitive to microenvironment, and Stokes shifts can be dominated by the well-known heterogeneous nature of protein structure, leading to what we call pseudo-TDFSS: shifts that arise from differential decay rates of subpopulations. Here we emphasize a novel, general method that obviates pseudo-TDFSS by replacing Trp by 5-fluorotryptophan (5Ftrp), a fluorescent analogue with higher ionization potential and greatly suppressed electron-transfer quenching. 5FTrp slows and suppresses pseudo-TDFSS, thereby providing a clearer view of genuine relaxation caused by solvent and protein response. This procedure is applied to the sweet-tasting protein monellin which has uniquely been the subject of ultrafast studies in two different laboratories (Peon, J.; et al. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 10964; Xu, J.; et al. J. Am. Chem. Soc. 2006, 128, 1214) that led to disparate interpretations of a 20 ps transient. They differed because of the pseudo-TDFSS present. The current study exploiting special properties of 5FTrp strongly supports the conclusion that both lifetime heterogeneity-based TDFSS and environment relaxation-based TDFSS are present in monellin and 5FTrp-monellin. The original experiments on monellin were most likely dominated by pseudo-TDFSS, whereas, in the present investigation of 5FTrp-monellin, the TDFSS is dominated by relaxation and any residual pseudo-TDFSS is overwhelmed and/or slowed to irrelevance.
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Affiliation(s)
- Jianhua Xu
- Optical Spectroscopy Section, Laboratory of Molecular Biophysics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Binbin Chen
- Optical Spectroscopy Section, Laboratory of Molecular Biophysics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Patrik Callis
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Pedro L. Muiño
- Department of Chemistry, Saint Francis University, Loretto, Pennsylvania 15940, United States
| | - Henriëtte Rozeboom
- Department of Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Jaap Broos
- Department of Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Dmitri Toptygin
- Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Ludwig Brand
- Department of Biology, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Jay R. Knutson
- Optical Spectroscopy Section, Laboratory of Molecular Biophysics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
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7
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Biesso A, Xu J, Muíño PL, Callis PR, Knutson JR. Charge invariant protein-water relaxation in GB1 via ultrafast tryptophan fluorescence. J Am Chem Soc 2014; 136:2739-47. [PMID: 24456037 PMCID: PMC4004251 DOI: 10.1021/ja406126a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
![]()
The
protein–water interface is a critical determinant of
protein structure and function, yet the precise nature of dynamics
in this complex system remains elusive. Tryptophan fluorescence has
become the probe of choice for such dynamics on the picosecond time
scale (especially via fluorescence “upconversion”).
In the absence of ultrafast (“quasi-static”) quenching
from nearby groups, the TDFSS (time-dependent fluorescence Stokes
shift) for exposed Trp directly reports on dipolar relaxation near
the interface (both water and polypeptide). The small protein GB1
contains a single Trp (W43) of this type, and its structure is refractory
to pH above 3. Thus, it can be used to examine the dependence of dipolar
relaxation upon charge reconfiguration with titration. Somewhat surprisingly,
the dipolar dynamics in the 100 fs to 100 ps range were unchanged
with pH, although nanosecond yield, rates, and access all changed.
These results were rationalized with the help of molecular dynamics
(including QM-MM) simulations that reveal a balancing, sometimes even
countervailing influence of protein and water dipoles. Interestingly,
these simulations also showed the dominant influence of water molecules
which are associated with the protein interface for up to 30 ps yet
free to rotate at approximately “bulk” water rates.
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Affiliation(s)
- Arianna Biesso
- Optical Spectroscopy Section, Laboratory of Molecular Biophysics, National Heart, Lung and Blood Institute, National Institutes of Health , Bethesda, Maryland 20892, United States
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8
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Abstract
(1)H-, (11)B-, (13)C-, (15)N-, (17)O-, (19)F-, and (31)P-NMR chemical shifts of flavocoenzymes and derivatives of it, as well as of alloxazines and isoalloxazinium salts, from NMR experiments performed under various experimental conditions (e.g., dependence of the chemical shifts on temperature, concentration, solvent polarity, and pH) are reported. Also solid-state (13)C- and (15)N-NMR experiments are described revealing the anisotropic values of corresponding chemical shifts. These data, in combination with a number of coupling constants, led to a detailed description of the electronic structure of oxidized and reduced flavins. The data also demonstrate that the structure of oxidized flavin can assume a configuration deviating from coplanarity, depending on substitutions in the isoalloxazine ring, while that of reduced flavin exhibits several configurations, from almost planar to quite bended. The complexes formed between oxidized flavin and metal ions or organic molecules revealed three coordination sites with metal ions (depending on the chemical nature of the ion), and specific interactions between the pyrimidine moiety of flavin and organic molecules, mimicking specific interactions between apoflavoproteins and their coenzymes. Most NMR studies on flavoproteins were performed using (13)C- and (15)N-substituted coenzymes, either specifically enriched in the pterin moiety of flavin or uniformly labeled flavins. The chemical shifts of free flavins are used as a guide in the interpretation of the chemical shifts observed in flavoproteins. Although the hydrogen-bonding pattern in oxidized and reduced flavoproteins varies considerably, no correlation is obvious between these patterns and the corresponding redox potentials. In all reduced flavoproteins the N(1)H group of the flavocoenzyme is deprotonated, an exception is thioredoxin reductase. Three-dimensional structures of only a few flavoproteins, mostly belonging to the family of flavodoxins, have been solved. Also the kinetics of unfolding and refolding of flavodoxins has been investigated by NMR techniques. In addition, (31)P-NMR data of all so far studied flavoproteins and some (19)F-NMR spectra are discussed.
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Affiliation(s)
- Franz Müller
- , Wylstrasse 13, CH-6052, Hergiswil, Switzerland,
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9
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Abstract
Biosynthetic incorporation of Trp analogs in a protein can help in its characterization using fluorescence spectroscopy and other methodologies like NMR and phosphorescence. Here a protocol is presented resulting in the efficient incorporation of Trp analogs in a recombinant protein, using an Escherichia coli Trp auxotroph. An overview of recent developments in the Trp analog incorporation field is also presented.
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Affiliation(s)
- Jaap Broos
- Laboratory of Biophysical Chemistry and Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
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10
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Opačić M, Hesp BH, Fusetti F, Dijkstra BW, Broos J. Structural investigation of the transmembrane C domain of the mannitol permease from Escherichia coli using 5-FTrp fluorescence spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:861-8. [PMID: 22100747 DOI: 10.1016/j.bbamem.2011.11.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 10/01/2011] [Accepted: 11/02/2011] [Indexed: 11/18/2022]
Abstract
The mannitol transporter EII(mtl) from Escherichia coli is responsible for the uptake of mannitol over the inner membrane and its concomitant phosphorylation. EII(mtl) is functional as a dimer and its membrane-embedded C domain, IIC(mtl), harbors one high affinity mannitol binding site. To characterize this domain in more detail the microenvironments of thirteen residue positions were explored by 5-fluorotryptophan (5-FTrp) fluorescence spectroscopy. Because of the simpler photophysics of 5-FTrp compared to Trp, one can distinguish between the two 5-FTrp probes present in dimeric IIC(mtl). At many labeled positions, the microenvironment of the 5-FTrps in the two protomers differs. Spectroscopic properties of three mutants labeled at positions 198, 251, and 260 show that two conserved motifs (Asn194-His195 and Gly254-Ile255-His256-Glu257) are located in well-structured parts of IIC(mtl). Mannitol binding has a large impact on the structure around position 198, while only minor changes are induced at positions 251 and 260. Phosphorylation of the cytoplasmic B domain of EII(mtl) is sensed by 5-FTrp at positions 30, 42, 251 and 260. We conclude that many parts of the IIC(mtl) structure are involved in the sugar translocation. The structure of EII(mtl), as investigated in this work, differs from the recently solved structure of a IIC protein transporting diacetylchitobiose, ChbC, and also belonging to the glucose superfamily of EII sugar transporters. In EII(mtl), the sugar binding site is more close to the periplasmic face and the structure of the 2 protomers in the dimer is different, while both protomers in the ChbC dimer are essentially the same.
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Affiliation(s)
- Milena Opačić
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, AG Groningen, The Netherlands
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11
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Sarkar SS, Udgaonkar JB, Krishnamoorthy G. Reduced Fluorescence Lifetime Heterogeneity of 5-Fluorotryptophan in Comparison to Tryptophan in Proteins: Implication for Resonance Energy Transfer Experiments. J Phys Chem B 2011; 115:7479-86. [DOI: 10.1021/jp2016984] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Saswata Sankar Sarkar
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - Jayant B. Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - G. Krishnamoorthy
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
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12
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Laptenok SP, Visser NV, Engel R, Westphal AH, van Hoek A, van Mierlo CPM, van Stokkum IHM, van Amerongen H, Visser AJWG. A General Approach for Detecting Folding Intermediates from Steady-State and Time-Resolved Fluorescence of Single-Tryptophan-Containing Proteins. Biochemistry 2011; 50:3441-50. [PMID: 21425856 DOI: 10.1021/bi101965d] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sergey P. Laptenok
- Department of Physics and Astronomy, Faculty of Exact Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
| | | | | | | | | | | | - Ivo H. M. van Stokkum
- Department of Physics and Astronomy, Faculty of Exact Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
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13
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Kitevski-LeBlanc JL, Evanics F, Scott Prosser R. Optimizing ¹⁹F NMR protein spectroscopy by fractional biosynthetic labeling. JOURNAL OF BIOMOLECULAR NMR 2010; 48:113-121. [PMID: 20734112 DOI: 10.1007/s10858-010-9443-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Accepted: 07/27/2010] [Indexed: 05/29/2023]
Abstract
In protein NMR experiments which employ nonnative labeling, incomplete enrichment is often associated with inhomogeneous line broadening due to the presence of multiple labeled species. We investigate the merits of fractional enrichment strategies using a monofluorinated phenylalanine species, where resolution is dramatically improved over that achieved by complete enrichment. In NMR studies of calmodulin, a 148 residue calcium binding protein, ¹⁹F and ¹H-¹⁵N HSQC spectra reveal a significant extent of line broadening and the appearance of minor conformers in the presence of complete (>95%) 3-fluorophenylalanine labeling. The effects of varying levels of enrichment of 3-fluorophenylalanine (i.e. between 3 and >95%) were further studied by ¹⁹F and ¹H-¹⁵N HSQC spectra, ¹⁵N T(1) and T(2) relaxation measurements, ¹⁹F T(2) relaxation, translational diffusion and heat denaturation experiments via circular dichroism. Our results show that while several properties, including translational diffusion and thermal stability show little variation between non-fluorinated and >95% ¹⁹F labeled samples, ¹⁹F and ¹H-¹⁵N HSQC spectra show significant improvements in line widths and resolution at or below 76% enrichment. Moreover, high levels of fluorination (>80%) appear to increase protein disorder as evidenced by backbone ¹⁵N dynamics. In this study, reasonable signal to noise can be achieved between 60-76% ¹⁹F enrichment, without any detectable perturbations from labeling.
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Affiliation(s)
- Julianne L Kitevski-LeBlanc
- Department of Chemistry, University of Toronto, UTM, 3359 Mississauga Rd., North Mississauga, ON L5L1C6, Canada
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14
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Opacić M, Vos EPP, Hesp BH, Broos J. Localization of the substrate-binding site in the homodimeric mannitol transporter, EIImtl, of Escherichia coli. J Biol Chem 2010; 285:25324-31. [PMID: 20522557 DOI: 10.1074/jbc.m110.122523] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mannitol transporter from Escherichia coli, EII(mtl), belongs to a class of membrane proteins coupling the transport of substrates with their chemical modification. EII(mtl) is functional as a homodimer, and it harbors one high affinity mannitol-binding site in the membrane-embedded C domain (IIC(mtl)). To localize this binding site, 19 single Trp-containing mutants of EII(mtl) were biosynthetically labeled with 5-fluorotryptophan (5-FTrp) and mixed with azi-mannitol, a substrate analog acting as a Förster resonance energy transfer (FRET) acceptor. Typically, for mutants showing FRET, only one 5-FTrp was involved, whereas the 5-FTrp from the other monomer was too distant. This proves that the mannitol-binding site is asymmetrically positioned in dimeric IIC(mtl). Combined with the available two-dimensional projection maps of IIC(mtl), it is concluded that a second resting binding site is present in this transporter. Active transport of mannitol only takes place when EII(mtl) becomes phosphorylated at Cys(384) in the cytoplasmic B domain. Stably phosphorylated EII(mtl) mutants were constructed, and FRET experiments showed that the position of mannitol in IIC(mtl) remains the same. We conclude that during the transport cycle, the phosphorylated B domain has to move to the mannitol-binding site, located in the middle of the membrane, to phosphorylate mannitol.
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Affiliation(s)
- Milena Opacić
- Laboratory of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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