A Solid-State 17O NMR Study of l-Tyrosine in Different Ionization States: Implications for Probing Tyrosine Side Chains in Proteins (original) (raw)
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Journal of Physical Chemistry B, 2010
We report experimental characterization of 17 O quadrupole coupling (QC) and chemical shift (CS) tensors for the phenolic oxygen in three L-tyrosine (L-Tyr) compounds: L-Tyr, L-Tyr • HCl, and Na 2 (L-Tyr). This is the first time that these fundamental 17 O NMR tensors are completely determined for phenolic oxygens in different ionization states. We find that, while the 17 O QC tensor changes very little upon phenol ionization, the 17 O CS tensor displays a remarkable sensitivity. In particular, the isotropic 17 O chemical shift increases by approximately 60 ppm upon phenol ionization, which is 6 times larger than the corresponding change in the isotropic 13 C chemical shift for the C nucleus of the same phenol group. By examining the CS tensor orientation in the molecular frame of reference, we discover a "cross-over" effect between δ 11 and δ 22 components for both 17 O and 13 C CS tensors. We demonstrate that the knowledge of such "cross-over" effects is crucial for understanding the relationship between the observed CS tensor components and chemical bonding. Our results suggest that solid-state 17 O NMR can potentially be used to probe the ionization state of tyrosine side chains in proteins.
Journal of the American Chemical Society, 2012
We report a comprehensive variable-temperature solid-state 17 O NMR study of three 17 O-labeled crystalline sulfonic acids: 2-aminoethane-1-sulfonic acid (taurine, T), 3aminopropane-1-sulfonic acid (homotaurine, HT), and 4-aminobutane-1-sulfonic acid (ABSA). In the solid state, all three compounds exist as zwitterionic structures, NH 3 + −R−SO 3 − ,i n which the SO 3 − group is involved in various degrees of O•••H−N hydrogen bonding. High-quality 17 O NMR spectra have been obtained for all three compounds under both static and magic angle spinning (MAS) conditions at 21.1 T, allowing the complete set of 17 O NMR tensor parameters to be measured. Assignment of the observed 17 O NMR parameters to the correct oxygen sites in the crystal lattice was achieved with the aid of DFT calculations. By modeling the temperature dependence of 17 O NMR powder line shapes, we have not only confirmed that the SO 3 − groups in these compounds undergo a 3-fold rotational jump mechanism but also extracted the corresponding jump rates (10 2 −10 5 s −1) and the associated activation energies (E a) for this process (E a =4 8± 7, 42 ± 3, and 45 ± 1 kJ mol −1 for T, HT, and ABSA, respectively). This is the first time that SO 3 − rotational dynamics have been directly probed by solid-state 17 O NMR. Using the experimental activation energies for SO 3 − rotation, we were able to evaluate quantitatively the total hydrogen bond energy that each SO 3 − group is involved in within the crystal lattice. The activation energies also correlate with calculated rotational energy barriers. This work provides a clear illustration of the utility of solid-state 17 O NMR in quantifying dynamic processes occurring in organic solids. Similar studies applied to selectively 17 O-labeled biomolecules would appear to be very feasible.
A review of oxygen-17 solid-state NMR of organic materials—towards biological applications
2004
17O solid state NMR of organic materials is developing rapidly. This article provides a snapshot of the current state of development of this field. The NMR techniques and enrichment protocols that are driving this progress are outlined. The 17O parameters derived from solid-state NMR experiments are summarized and the structural sensitivity of the approach to effects such as hydrogen bonding highlighted. The prospects and challenges for 17O solid-state NMR of biomolecules are discussed.
Probing O–H Bonding through Proton Detected 1H–17O Double Resonance Solid-State NMR Spectroscopy
Journal of the American Chemical Society, 2018
The ubiquity of oxygen in organic, inorganic, and biological systems has stimulated the application and development of 17O solid-state NMR spectroscopy as a probe of molecular structure and dynamics. Unfortunately, 17O solid-state NMR experiments are often hindered by the combination of broad NMR signals and low sensitivity. Here, it is demonstrated that fast MAS and proton detection with the D-RINEPT pulse sequence can be generally applied to enhance the sensitivity and resolution of 17O solid-state NMR experiments. Complete 2D 17O→1H D-RINEPT correlation NMR spectra were typically obtained in fewer than 10 hours from less than 10 milligrams of material, with low to moderate 17O enrichment (less than 20%). 2D 1H-17O correlation solid-state NMR spectra allow overlapping oxygen sites to be resolved on the basis of proton chemical shifts or by varying the mixing time used for 1H-17O magnetization transfer. In addition, J-resolved or separated local field (SLF) blocks can be incorporated into the D-RINEPT pulse sequence to allow direct measurement of one-bond 1H-17O scalar coupling constants (1JOH) or 1H-17O dipolar couplings (DOH), respectively; the latter of which can be used to infer 1H-17O bond lengths. 1JOH and DOH calculated from planewave density functional theory (DFT) show very good agreement with experimental values. Therefore, the 2D 1H-17O correlation experiments, 1H-17O scalar and dipolar couplings, and planewave DFT calculations provide a method to precisely determine proton positions relative to oxygen atoms. This capability opens new opportunities to probe interactions between oxygen and hydrogen in a variety of chemical systems. Disciplines
Physical chemistry chemical physics : PCCP, 2011
Monosodium L-glutamate monohydrate, a multiple oxygen site (eight) compound, is used to demonstrate that a combination of high-resolution solid-state NMR spectroscopic techniques opens up new possibilities for (17)O as a nuclear probe of biomolecules. Eight oxygen sites have been resolved by double rotation (DOR) and multiple quantum (MQ) NMR experiments, despite the (17)O chemical shifts lying within a narrow shift range of <50 ppm. (17)O DOR NMR not only provides high sensitivity and spectral resolution, but also allows a complete set of the NMR parameters (chemical shift anisotropy and electric-field gradient) to be determined from the DOR spinning-sideband manifold. These (17)O NMR parameters provide an important multi-parameter comparison with the results from the quantum chemical NMR calculations, and enable unambiguous oxygen-site assignment and allow the hydrogen positions to be refined in the crystal lattice. The difference in sensitivity between DOR and MQ NMR experimen...
Tetrahedron Letters, 2004
The hypothesis and the conclusions of previous 17 O NMR studies on the detection of both oxygens of the carboxylic group of Boc-[ 17 O]Tyr(2,6-diClBzl)-OH in DMSO-d 6 solution (V. Tsikaris et al., Tetrahedron Lett. 2000, 41, 8651) are reconsidered. The appearance of two discrete resonances at 340 and 175 ppm of this protected amino acid is not now attributed: (a) to the reduction of the intramolecular conformational exchange rate, due to the effect of intramolecular hydrogen bonding of the hydroxy part of the carboxyl with the carbonyl oxygen of the Boc-group, and (b) to the effect of solvent viscosity, suggested in the mentioned study. The cause of this phenomenon is now attributed to a strong hydrogen bonding of the polar proton acceptor solvent DMSO with the carboxy group, which effectively reduces the proton exchange rate, thus becoming slow on the 17 O NMR time scale. Ó 2004 Elsevier Ltd. All rights reserved. 17 O NMR spectroscopy provides a powerful and sensitive tool for studying intra-and intermolecular hydrogen bonding effects both in solution and in the solid state. 1-4 Since the oxygen atom is one of the most important atoms constituting hydrogen-bonding structures, 17 O NMR might provide novel and complementary information not readily available from other methods.
Solid-state 17O NMR of amino acids
2004
17O solid-state NMR from 14 amino acids is reported here, greatly increasing the number investigated. In most cases well-separated resonances from carbonyl and hydroxyl oxygens with distinct second-order quadrupolar line shapes are observed using a 600 MHz spectrometer with fast magic angle spinning (MAS). This is in contrast to the motionally averaged resonances usually seen from amino acids in solution.
Biochemistry, 1992
Solid-state 13C magic angle spinning (MAS) NMR has been used to investigate detergentsolubilized photosynthetic reaction centers of Rhodobacter sphaeroides R26, selectively enriched in [4J3C]tyrosine. The reaction centers were frozen, in the dark and while subject to intense illumination, and studied at temperatures between -21 5 and -260 K. The signal consists of at least seven narrow lines superimposed on a broad doublet. The chemical shift anisotropy is similar to that for crystalline tyrosine. The two narrowest resonances, corresponding to signals from individual tyrosines, are 28 f 5 Hz wide, comparable to what is observed for quaternary carbons in linearly elastic organic solids. The line width as well as the chemical shift of these signals is essentially independent of temperature. This provides strong evidence for an unusually ordered, well-shielded, and structurally, electrostatically, and thermodynamically stable interior of the protein complex without structural heterogeneities. As the temperature is lowered, additional signal from the labels develops and the natural abundance resonances from the detergent broaden, providing evidence for considerable flexibility at the exterior of the protein complex and in the detergent belt at the higher temperatures. In addition, the NMR provides evidence for an electrostatically uniform and neutral complex, since the total dispersion in isotropic shifts for the labels is <5 ppm and corresponds to electron densicy variations of less than 0.03 electronic equivalents with respect to tyrosine in the solid state or in t
Oxygen is an integral component of proteins and nucleic acids, but remains sparsely studied in such samples because its only NMR active isotope, 17O, is a low sensitivity and resolution species. These properties are a consequence of its low natural abundance (0.039%) and the fact that 17O is a S = 5/2 nuclide with large quadrupolar couplings (6-11 MHz). In this work, we address these issues with efficient isotopic labeling, high magnetic fields, fast magic-angle spinning and indirect 1H detection. This combination of refinements, in conjunction with multidimensional heteronuclear correlation experiments, improves sensitivity and permits observation of oxygen sites specific to each amino acid residue in a model dipeptide sample in a manner consistent with the goal of high resolution. In particular, double-quantum cross-polarization at high sample spinning frequencies is found to provide efficient polarization transfer between 13C and 17O nuclei. Notably, the use of 17O as the initial...