Magic Angle Spinning NMR Data Research Articles

Mapping Hydrogens in Hydrous Materials

Hydrous materials such as clays, cements, hydroxyapatite, and metal hydroxides have been known and extensively used since antiquity. However, experimental elucidation of hydrogen in hydrous materials remains challenging due to the intrinsic insensitivity, limited accessibility, sample damage, or poor spectral resolution of many characterization methods. 1H solid-state NMR spectroscopy has evolved into an ideal site-specific characterization tool of hydrogen-containing materials, but its current application in hydrous materials is hampered by the low resolution of 1H NMR spectra in the solid state due to the presence of intense dipolar coupling networks and a narrow 1H chemical shift range. Herein, a significant advance in the characterization of hydrogens in hydrous materials is reported. A combination of magic-angle spinning (MAS) NMR, moderate 2H substitution, and high magnetic fields has unlocked the capacity of identifying many chemically similar while crystallographically distinct hydrogen sites in a prototypical hydrous material Y4(OH)10Br2·3H2O (LYH-Br) by 1D 1H solid-state NMR experiments. 1H NMR peaks were first tentatively assigned in accordance with the density functional theory (DFT) calculation results, and the assignment was further refined by 2D 1H–89Y heteronuclear correlation (HETCOR) and 1H–1H double-quantum (DQ) MAS NMR data. The order of 1H chemical shift (δiso) values provides valuable information on the relative strength of hydrogen bond for ten hydroxide hydrogen sites. The power of very high spectral resolution is further described by observing all triple-quantum (TQ) coherences in the 2D 1H–1H TQ MAS NMR spectrum, in which all spatial proximities among three hydrogen sites are resolved. This demonstration of the very high spectral resolution obtained in 1D and 2D 1H solid-state NMR experiments illustrates how scientists in various communities can now study the multiple hydrous species of hydrous materials and obtain previously inaccessible fine structural information.

Structure and Gating Behavior of the Human Integral Membrane Protein VDAC1 in a Lipid Bilayer.

The voltage-dependent anion channel (VDAC), the most abundant protein in the outer mitochondrial membrane, is responsible for the transport of all ions and metabolites into and out of mitochondria. Larger than any of the β-barrel structures determined to date by magic-angle spinning (MAS) NMR, but smaller than the size limit of cryo-electron microscopy (cryo-EM), VDAC1’s 31 kDa size has long been a bottleneck in determining its structure in a near-native lipid bilayer environment. Using a single two-dimensional (2D) crystalline sample of human VDAC1 in lipids, we applied proton-detected fast magic-angle spinning NMR spectroscopy to determine the arrangement of β strands. Combining these data with long-range restraints from a spin-labeled sample, chemical shift-based secondary structure prediction, and previous MAS NMR and atomic force microscopy (AFM) data, we determined the channel’s structure at a 2.2 Å root-mean-square deviation (RMSD). The structure, a 19-stranded β-barrel, with an N-terminal α-helix in the pore is in agreement with previous data in detergent, which was questioned due to the potential for the detergent to perturb the protein’s functional structure. Using a quintuple mutant implementing the channel’s closed state, we found that dynamics are a key element in the protein’s gating behavior, as channel closure leads to the destabilization of not only the C-terminal barrel residues but also the α2 helix. We showed that cholesterol, previously shown to reduce the frequency of channel closure, stabilizes the barrel relative to the N-terminal helix. Furthermore, we observed channel closure through steric blockage by a drug shown to selectively bind to the channel, the Bcl2-antisense oligonucleotide G3139.

15N photo-CIDNP MAS NMR analysis of a bacterial photosynthetic reaction center of Rhodobacter sphaeroides wildtype.

The solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect has been studied in a quinone-depleted uniformly (u-)13C,15N-labeled photosynthetic reaction center (RC) protein from purple bacterium Rhodobacter (R.) sphaeroides wild type (WT). As a method for investigation, solid-state 15N NMR under magic-angle spinning (MAS) is applied under both continuous illumination (steady state) and nanosecond-laser flashes (time-resolved). While all previous 15N photo-CIDNP MAS NMR studies on the purple bacterial RC used the carotenoid-less mutant R26, this is the first using WT samples. The absence of further photo-CIDNP mechanisms (compared to R26) and various couplings (compared to 13C NMR experiments on 13C-labeled samples) allows the simplification of the spin-system. We report 15N signals of the three cofactors forming the spin-correlated radical pair (SCRP) and, based on density-functional theory calculations, their assignment. The simulation of photo-CIDNP intensities and time-resolved 15N photo-CIDNP MAS NMR data matches well to the frame of the mechanistic interpretation. Three spin-chemical processes, namely, radical pair mechanism, three spin mixing, and differential decay, generate emissive (negative) 15N polarization in the singlet decay channel and absorptive (positive) polarization in the triplet decay channel of the SCRP. The absorptive 15N polarization of the triplet decay channel is transiently obscured during the lifetime of the triplet state of the carotenoid (3Car); therefore, the observed 15N signals are strongly emissive. Upon decay of 3Car, the transiently obscured polarization becomes visible by reducing the excess of emissive polarization. After the decline of 3Car, the remaining nuclear hyperpolarization decays with nuclear T1 relaxation kinetics.

Structure of Ancient Glass by 29 Si Magic Angle Spinning NMR Spectroscopy.

29 Si magic angle spinning (MAS) NMR spectroscopy has been applied for the first time to the structural analysis of ancient glass samples obtained from archaeological excavations. The results show that it is possible to establish the distribution of Si environments in ancient glass by 29 Si MAS NMR, so long as the concentrations of magnetic impurities, such as Mn and Fe oxides, are low. In general, good agreement has been obtained with compositions determined by means of electron probe microanalysis. In addition, the 29 Si MAS NMR data reveal structural differences between glasses manufactured at separate ancient sites.

Deuterium MAS NMR and Local Molecular Dynamic Model to Study Adsorption–Desorption Kinetics of a Dipeptide at the Inner Surfaces of SBA-15

This work presents a deuterium magic angle spinning (MAS) NMR study of the adsorption–desorption dynamics of glycine-(2,2)-d2-alanine dipeptide adsorbed at the inner surfaces of mesoporous SBA-15 silica under different hydration levels and temperatures. The experimental and theoretical challenges posed by the strong quadrupolar interaction of the rigid CD2 group, 3-fold bigger than that of the rotating methyl CD3, were addressed. Deuterium MAS NMR spectra modulated by exchange were analyzed using theoretically calculated exchange spectra based on the two-site Bloch–McConnel exchange equation represented in Floquet space. To solve this equation, which is composed of a high dimensional Floquet exchange matrix, our former computational approach was modified to reduce the overall computation time by orders of magnitude so as to yield more accurate exchange parameters from the spectral analysis. The adsorption–desorption kinetics of minutely hydrated silica surfaces is understood to originate from the diffusion of water molecules into and out of adsorbate binding sites, thereby gating the dynamic behavior of the adsorbate via increase or reduction of the size of the surrounding water cluster. Molecular dynamic (MD) simulations were employed to model the dynamic behavior of the adsorbate at the two states. Deviations between the MD and experimental observations are attributed to the simplified surface modeling, thereby highlighting the importance of experimental MAS NMR data to improve future modeling of realistic functional surfaces.

Structure of a Three Helix Membrane Protein from Oriented Sample and Magic Angle Spinning NMR Data

Of the many membrane protein structures deposited in the Protein Data Bank, only a few are of small helical proteins. Unfortunately, the typical transmembrane helix content of membrane proteins in the genomes of pathogenic bacteria is largely biased towards those with four or fewer helices. Many of these proteins are known or potential drug targets. The common structural techniques of x-ray crystallography and solution state NMR have had limited success in the determination of these structures [1]. Solid state NMR has emerged as a powerful tool capable of characterizing membrane protein structure in lipid bilayers. Oriented sample solid state NMR provides a set of peptide plane orientations. Magic angle spinning solid state NMR provides a set of interhelical distance restraints. Here, we show that together these restraints are capable of determining a backbone structure for the transmembrane domain of a three helix membrane protein. Furthermore, the structure orientation in the lipid bilayer is uniquely determined when using oriented sample restraints. We applied these methods to the Rv1861 protein from Mycobacterium tuberculosis, the causative agent of tuberculosis which is responsible for over one million deaths annually. Altogether, these experiments show that high resolution structures can be routinely determined for three to four helix membrane proteins and will help fill the void in the Protein Data Bank for these important drug targets.[1] Cross, T.A., Murray, D.T. and Watts, A. Eur. Biophys. J. In Press (2013) DOI 10.1007/s00249-013-0925-x.

Identifying lithium–air battery discharge products through 6Li solid-state MAS and 1H–13C solution NMR spectroscopy

Discharged lithium–O2 battery cathodes are investigated with different catalysts present including Pd, α-MnO2 and CuO, and containing two different electrolyte solvents, 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) and tetraethylene glycol dimethyl ether (TEGDME). Solid-state 6Li magic angle spinning (MAS) NMR spectroscopy has been used identify lithium products that are formed in the cathodes and differences between products formed with the different catalysts and solvents. There are significant differences in the products formed in Li–O2 cathodes with the two different solvents, EC/DMC and TEGDME. Due to the small chemical shift range of lithium it is difficult to determine exact speciation from 6Li MAS NMR data alone. Fitting of the 6Li NMR peaks with tested Li-oxide powder standards indicates that Li–O2 cathodes discharged in EC/DMC produce primarily Li2CO3 as a lithium product and those discharged in TEGDME produce mainly Li2O2. Solution 2D correlation 1H–13C NMR spectroscopy techniques allow for determination of side-products produced in Li–O2 cathodes.

A structural investigation of the alkali metal site distribution within bioactive glass using neutron diffraction and multinuclear solid state NMR

The atomic-scale structure of Bioglass and the effect of substituting lithium for sodium within these glasses have been investigated using neutron diffraction and solid state magic angle spinning (MAS) NMR. Applying an effective isomorphic substitution difference function to the neutron diffraction data has enabled the Na-O and Li-O nearest-neighbour correlations to be isolated from the overlapping Ca-O, O-(P)-O and O-(Si)-O correlations. These results reveal that Na and Li behave in a similar manner within the glassy matrix and do not disrupt the short range order of the network former. Residual differences are attributed solely to the variation in ionic radius between the two species. Successful simplification of the 2 < r (Å) < 3 region via the difference method has enabled all the nearest neighbour correlations to be deconvolved. The diffraction data provides the first direct experimental evidence of split Na-O nearest-neighbour correlations in these melt quench bioactive glasses, and an analogous splitting of the Li-O correlations. The observed correlations are attributed to the metal ions bonded either to bridging or to non-bridging oxygen atoms. (23)Na triple quantum MAS (3QMAS) NMR data corroborates the split Na-O correlations. The structural sites present will be intimately related to the release properties of the glass system in physiological fluids such as plasma and saliva, and hence to the bioactivity of the material. Detailed structural knowledge is therefore a prerequisite for optimizing material design.

A software framework for analysing solid-state MAS NMR data.

Solid-state magic-angle-spinning (MAS) NMR of proteins has undergone many rapid methodological developments in recent years, enabling detailed studies of protein structure, function and dynamics. Software development, however, has not kept pace with these advances and data analysis is mostly performed using tools developed for solution NMR which do not directly address solid-state specific issues. Here we present additions to the CcpNmr Analysis software package which enable easier identification of spinning side bands, straightforward analysis of double quantum spectra, automatic consideration of non-uniform labelling schemes, as well as extension of other existing features to the needs of solid-state MAS data. To underpin this, we have updated and extended the CCPN data model and experiment descriptions to include transfer types and nomenclature appropriate for solid-state NMR experiments, as well as a set of experiment prototypes covering the experiments commonly employed by solid-sate MAS protein NMR spectroscopists. This work not only improves solid-state MAS NMR data analysis but provides a platform for anyone who uses the CCPN data model for programming, data transfer, or data archival involving solid-state MAS NMR data.Electronic supplementary materialThe online version of this article (doi:10.1007/s10858-011-9569-2) contains supplementary material, which is available to authorized users.

Structural elucidation of β-(Y,Sc)2Si2O7: combined use of89Y MAS NMR and powder diffraction

Although the structures of pure Sc2Si2O7and β-Y2Si2O7have been described in the literature using theC2/mspace group,29Si magic angle spinning (MAS) NMR measurements of the intermediate members of the Sc2Si2O7–β-Y2Si2O7system indicate a lowering of the symmetry to theC2 space group. Indeed, these compositions exhibit a unique Si crystallographic site and an Si—O—Si angle lower than 180°, incompatible with theC2/mspace group.C2 is the only possible alternative. Space groupCmcan be discarded with regard to its two different Si sites per unit cell. Moreover,89Y MAS NMR data have revealed the existence of two different Y sites in the structure of the intermediate members of the Sc2Si2O7–β-Y2Si2O7system, confirming the lowering of the symmetry to theC2 space group. The viability of theC2 model has therefore been tested and confirmed by refinement of synchrotron and neutron powder diffraction data for the different members of the system. The structural evolutions across the Sc2Si2O7–β-Y2Si2O7system are discussed.

Structural characterization of GNNQQNY amyloid fibrils by magic angle spinning NMR.

Several human diseases are associated with the formation of amyloid aggregates, but experimental characterization of these amyloid fibrils and their oligomeric precursors has remained challenging. Experimental and computational analysis of simpler model systems has therefore been necessary, for instance, on the peptide fragment GNNQQNY7−13 of yeast prion protein Sup35p. Expanding on a previous publication, we report here a detailed structural characterization of GNNQQNY fibrils using magic angle spinning (MAS) NMR. On the basis of additional chemical shift assignments we confirm the coexistence of three distinct peptide conformations within the fibrillar samples, as reflected in substantial chemical shift differences. Backbone torsion angle measurements indicate that the basic structure of these coexisting conformers is an extended β-sheet. We structurally characterize a previously identified localized distortion of the β-strand backbone specific to one of the conformers. Intermolecular contacts are consistent with each of the conformers being present in its own parallel and in-register sheet. Overall the MAS NMR data indicate a substantial difference between the structure of the fibrillar and crystalline forms of these peptides, with a clearly increased complexity in the GNNQQNY fibril structure. These experimental data can provide guidance for future work, both experimental and theoretical, and provide insights into the distinction between fibril growth and crystal formation.

Electron−Nuclear Spin Dynamics in a Bacterial Photosynthetic Reaction Center

The solid-state photo-CIDNP effect is known to occur in natural photosynthetic reaction centers (RCs) where it can be observed by magic-angle spinning (MAS) NMR as strong modification of signal intensities under illumination compared to experiments performed in the dark. The origin of the effect has been debated. In this paper, we report time-resolved photo-CIDNP MAS NMR data of reaction centers of quinone depleted Rhodobacter sphaeroides. It is demonstrated that the build-up of nuclear polarization on the primary donor and the bacteriopheophytin acceptor depends on the presence and lifetimes of the molecular triplet states of the donor and carotenoid. Analysis of the data proves that up to three electron−nuclear spin-coupling mechanisms and two transient effects are working concomitantly in the spin-chemical machinery of the reaction center.

17O and 15N Solid State NMR Studies on Ligand-Assisted Templating and Oxygen Coordination in the Walls of Mesoporous Nb, Ta and Ti Oxides

A multinuclear solid state NMR approach is applied to four templated mesoporous oxides (silica, titania, niobia and tantala) to include (15)N and (17)O magic angle spinning (MAS) NMR and double resonance (15)N-(93)Nb, (17)O Rotational-Echo Adiabatic Passage Double Resonance (REAPDOR). The templated samples were ramped in steps of 20 degrees C for 2 days up to typically 110 degrees C where the samples were left for 2-4 days. (15)N MAS NMR shows that amines are the only species present in the TiO2, Nb2O5, and Ta2O5. In SiO2, amines are only present as a minor coordination (10 +/- 2%), but there are several strong ammonium (15)N resonances. The REAPDOR experiments show that the nitrogen interacts with niobium, confirming a ligand interaction between the Nb and N, as previously believed. In the case of silica, the amine is quaternized and there is apparently no interaction with the Si, suggesting a RNH3(+) (-)O-Si- hydrogen-bonding interaction with the walls. (17)O MAS NMR provides the clearest indication of the local wall structure. In the aged, templated samples in all cases only OM2 coordinations are present which is very different from the pure bulk oxides (apart from SiO2) and must be due to the effects of amine coordination at the metal centers. On removal of the template, these oxides behave differently, with Ta2O5 showing a mixture of OTa2 (85 +/- 5%) and OTa3 (15 +/- 5%) which is similar to the types of coordination found in the bulk oxide. The previously reported (17)O MAS NMR data from heat-treated mesoporous niobia shows only ONb2, which is very highly ordered. In contrast for titania, the OTi2 coordination is immediately lost on removal of the template to be replaced by a mixture of OTi3 (60 +/- 5%) and OTi4 (40 +/- 5%), with the OTi4 becoming dominant above 250 degrees C, very different behavior from the corresponding bulk oxide. In summary, this NMR study shows that the local oxygen coordination in amine-templated mesoporous transition metal oxides is present as OM2 which is relatively rare in bulk oxides. The data indicates that the template interaction is largely controlled by the N-M dative bond to the wall, suppressing higher oxygen coordination numbers. Qualitatively it appears that the strength of this interaction varies greatly in the different mesoporous oxides.

Mg/Al Ordering in Layered Double Hydroxides Revealed by Multinuclear NMR Spectroscopy

The anion-exchange ability of layered double hydroxides (LDHs) has been exploited to create materials for use in catalysis, drug delivery, and environmental remediation. The specific cation arrangements in the hydroxide layers of hydrotalcite-like LDHs, of general formula Mg2+(1-x)Al3+(x)OH2(Anion(n-)(x/n)).yH2O, have, however, remained elusive, and their elucidation could enhance the functional optimization of these materials. We applied rapid (60 kilohertz) magic angle spinning (MAS) to obtain high-resolution hydrogen-1 nuclear magnetic resonance (1H NMR) spectra and characterize the magnesium and aluminum distribution. These data, in combination with 1H-27Al double-resonance and 25Mg triple-quantum MAS NMR data, show that the cations are fully ordered for magnesium:aluminum ratios of 2:1 and that at lower aluminum content, a nonrandom distribution of cations persists, with no Al3+-Al3+ close contacts. The application of rapid MAS NMR methods to investigate proton distributions in a wide range of materials is readily envisaged.

Metal effects on the membrane interactions of amyloid-β peptides

A beta (1-42) peptide, found as aggregated species in Alzheimer's disease brain, is linked to the onset of dementia. We detail results of 31P and 2H solid-state NMR studies of model membranes with A beta peptides and the effect of metal ions (Cu2+ and Zn2+), which are found concentrated in amyloid plaques. The effects on the lipid bilayer and the peptide structure are different for membrane incorporated or associated peptides. Copper ions alone destabilise the lipid bilayer and induce formation of smaller vesicles, but not when A beta(1-42) is associated with the bilayer membrane. A beta (25-35), a fragment from the C-terminal end of A beta(1-42), which lacks the metal coordinating sites found in the full length peptide, is neurotoxic to cortical cortex cell cultures. Addition of metal ions has little effect on membrane bilayers with A beta (25-35) peptides. 31P magic angle spinning NMR data show that A beta (1-42) and A beta (1-42)-Cu2+ complexes interact at the surface of anionic phospholipid membranes. Incorporated peptides, however, appear to disrupt the membrane more severely than associated peptides. Solid-state 13C NMR was used to compare structural changes of A beta (1-42) to those of A beta (25-35) in model membrane systems of anionic phospholipids and cholesterol. The A beta peptides appeared to have an increase in beta-strand structure at the C-terminus when added to phospholipid liposomes. The inclusion of Cu2+ also influenced the observed chemical shift of residues from the C-terminal half, providing structural clues for the lipid-associated A beta/metal complex. The results point to the complex pathway(s) for toxicity of the full-length peptide.

Porous xerogels with a bifunctional surface layer of the composition ≡Si(CH2)3SH/≡Si(CH2)2H3

The sol-gel method with ethanol as a solvent and fluoride ion as a catalyst was used to prepare polysiloxane xerogels containing both 3-mercaptopropyl and n-propyl groups in the surface layer. An increase in the relative amount of n-propyltriethoxysilane in the initial reaction solution was found to result in the formation of xerogels with developed porous structures, which was accompanied by an increase in the specific surface area from 370 to 550 m2/g; simultaneously, other porous structure parameters such as sorption volume and pore size exhibited a tendency to increase. Atomic-force microscopy was used to show that the xerogels synthesized comprised aggregates of mean size 30 nm. An analysis of the IR and 13C cross-polarization magic angle spinning NMR data led us to conclude that the surface layer of bifunctional xerogels contained not only 3-mercaptopropyl and n-propyl groups but also silanol groups, part of nonhydrolyzed alkoxy groups, and H-bonded water molecules. The 29Si cross-polarization magic angle spinning NMR spectra revealed the presence of structural units of the compositions T1 [(≡SiO)Si(OR’)2(CH2CH2CH3) and/or (≡SiO)Si(OR’)2(CH2)3SH, R’ = H, OCH3, or OC2H5], T2 [(≡SiO)2Si(OR’)(CH2CH2CH3) and (≡SiO)2Si(OR’)(CH2)3SH], and T3 [(≡SiO)3SiCH2CH2CH3 and (≡SiO)3Si(CH2)3SH] in the xerogels synthesized.

Optimization, Standardization, and Testing of a New NMR Method for the Determination of Zeolite Host−Organic Guest Crystal Structures

An optimized and automated protocol for determining the location of guest sorbate molecules in highly siliceous zeolites from (29)Si INADEQUATE and (1)H/(29)Si cross polarization (CP) magic-angle spinning (MAS) NMR experiments is described. With the peaks in the (29)Si MAS NMR spectrum assigned to the unique Si sites in the zeolite framework by a 2D (29)Si INADEQUATE experiment, the location of the sorbate molecule is found by systematically searching for sorbate locations for which the measured rates of (1)H/(29)Si cross polarization of the different Si sites correlate linearly with (1)H/(29)Si second moments calculated from H-Si distances. Due to the (1)H/(29)Si cross polarization being in the "slow CP regime" for many zeolite-sorbate complexes, it is proposed that the CP rate constants are best measured by (1)H/(29)Si cross polarization drain experiments, if possible, to avoid complications that may arise from fast (1)H and (29)Si T(1)rho relaxations. An algorithm for determining the sorbate molecule location is described in detail. A number of ways to effectively summarize and display the large number of solutions which typically result from a prediction of the structure from the CP MAS NMR data are presented, including estimates of the errors involved in the structure determinations. As a working example throughout this paper, the structure of the low loaded p-dichlorobenzene/ZSM-5 complex is determined under different conditions from solid-state (1)H/(29)Si CP MAS NMR data, and the solutions are shown to be in excellent agreement with the known single-crystal X-ray diffraction structure. This structure determination approach is shown to be quite insensitive to the use of relative rate constants rather than absolute values, to the detailed structure of the zeolite framework, and relatively insensitive to temperature and motions.

The Diversity of the Liquid Ordered (L o) Phase of Phosphatidylcholine/Cholesterol Membranes: A Variable Temperature Multinuclear Solid-State NMR and X-Ray Diffraction Study

To investigate the properties of a pure liquid ordered (L o) phase in a model membrane system, a series of saturated phosphatidylcholines combined with cholesterol were examined by variable temperature multinuclear ( 1H, 2H, 13C, 31P) solid-state NMR spectroscopy and x-ray scattering. Compositions with cholesterol concentrations ≥40 mol %, well within the L o phase region, are shown to exhibit changes in properties as a function of temperature and cholesterol content. The 2H-NMR data of both cholesterol and phospholipids were used to more accurately map the L o phase boundary. It has been established that the gel-L o phase coexistence extends to 60 mol % cholesterol and a modified phase diagram is presented. Combined 1H-, 2H-, 13C-NMR, and x-ray scattering data indicate that there are large changes within the L o phase region, in particular, 1H-magic angle spinning NMR and wide-angle x-ray scattering were used to examine the in-plane intermolecular spacing, which approaches that of a fluid L α phase at high temperature and high cholesterol concentrations. Although it is well known for cholesterol to broaden the gel-to-fluid transition temperature, we have observed, from the 13C magic angle spinning NMR data, that the glycerol region can still undergo a “melting”, though this is broadened with increasing cholesterol content and changes with phospholipid chain length. Also from 2H-NMR order parameter data it was observed that the effect of temperature on chain length became smaller with increasing cholesterol content. Finally, from the cholesterol order parameter, it has been previously suggested that it is possible to determine the degree to which cholesterol associates with different phospholipids. However, we have found that by taking into account the relative temperature above the phase boundary this relationship may not be correct.

High‐Resolution Solid‐State NMR Studies on Uniformly [13C,15N]‐Labeled Ubiquitin

Understanding of the effects of intermolecular interactions, molecular dynamics, and sample preparation on high-resolution magic-angle spinning NMR data is currently limited. Using the example of a uniformly [13C,15N]-labeled sample of ubiquitin, we discuss solid-state NMR methods tailored to the construction of 3D molecular structure and study the influence of solid-phase protein preparation on solid-state NMR spectra. A comparative analysis of 13C', 13Calpha, and 13Cbeta resonance frequencies suggests that 13C chemical-shift variations are most likely to occur in protein regions that exhibit an enhanced degree of molecular mobility. Our results can be refined by additional solid-state NMR techniques and serve as a reference for ongoing efforts to characterize the structure and dynamics of (membrane) proteins, protein complexes, and other biomolecules by high-resolution solid-state NMR.

Photo-CIDNP solid-state NMR on Photosystems I and II:what makes P680 special?

The origin of the extraordinary high redox potential of P680, the primary electron donor of Photosystem II, is still unknown. Photochemically induced dynamic nuclear polarisation (photo-CIDNP) 13C magic-angle spinning (MAS) NMR is a powerful method to study primary electron donors. In order to reveal the electronic structure of P680, we compare new photo-CIDNP MAS NMR data of Photosystem II to those of Photosystem I. The comparison reveals that the electronic structure of the P680 radical cation is a Chl a cofactor with strong matrix interaction, while the radical cation of P700, the primary electron donor of Photosystem I, appears to be a Chl a cofactor which is essentially undisturbed. Possible forms of cofactor-matrix interactions are discussed.