"Kin " HEHAHA Sequences, Heteronuclear Hartmann-Hahn Transfer with Different Bandwidths for Spins I and S

Total Correlation Spectroscopy across All NMR-Active Nuclei by Mixing at Zero Field

Multidimensional nuclear magnetic resonance (NMR) is based on a combination of well-established building blocks for polarization transfer. These blocks are used to design correlation experiments through one or a few chemical bonds or through space. Here, we introduce a building block that enables polarization transfer across all NMR-active nuclei in a coupled network of spins: isotropic mixing at zero and ultralow field (ZULF). Exploiting mixing under ZULF-NMR conditions, heteronuclear TOtal Correlation SpectroscopY (TOCSY) experiments were developed to highlight coupled spin networks. We demonstrate ¹H-¹³C and ¹H-¹⁵N correlations in ZULF-TOCSY spectra of labeled amino acids, which allow one to obtain cross-peaks among all heteronuclei belonging to the same coupled network, even when the direct interaction between them is negligible. We also demonstrate the potential of ZULF-TOCSY to analyze complex mixtures on a growth medium of isotope-labeled biomolecules. ZULF-TOCSY enables the quick identification of individual compounds in the mixture by their coupled spin networks. The ZULF-TOCSY method will lead to the development of a new toolbox of experiments to analyze complex mixtures by NMR.

Selective heteronuclear Hartmann-Hahn: a multiple-pulse sequence for selective magnetization transfer in the structural elucidation of "isotagged" oligosaccharides

A new selective heteronuclear Hartmann-Hahn (SHEHAHA) multiple-pulse mixing sequence is proposed for the solution structure elucidation of milligram amounts of peracetylated oligosaccharides in which the acetyl groups are enriched in carbon-13, so-called "isotags". SHEHAHA accomplishes exclusive in-phase magnetization transfer between the isotag carbonyl (13)C and the proximal proton on the sugar ring. Relayed transfer around the sugar rings by proton-proton TOCSY is suppressed, while the heteronuclear transfer from the labeled carbonyl carbon to the proximal ring proton is maintained. The sequence is broadband in the sense that all acetyl groups simultaneously give good signal transfer to their respective nearest proton neighbors. The (1)H-detected spectra have decent sensitivity and excellent resolution, giving patterns that unambiguously identify common structural subunits in human glycans. Peracetylated maltitol is shown as a test case of the method. Lineshapes are pure absorption, allowing facile measurement of vicinal proton-proton couplings. Linkage points can be deduced, and the 2D correlation spectra may be useful for more ambitious prediction algorithms and machine identification by a spectral database.

Heteronuclear J cross-polarisation in liquids using amplitude and phase modulated mixing sequences

The design of mixing sequences for heteronuclear J cross-polarisation in the liquid state has been examined employing supercycles of amplitude/phase modulated RF pulses. The Fourier coefficients defining the modulation profiles of the pulses were optimised numerically so as to achieve efficient magnetisation transfer within the desired range of resonance offsets. A variety of supercycles, pulsewidths and RF field strengths were considered in implementing heteronuclear anisotropic and isotropic mixing sequences. The coherence transfer characteristics of the sequences obtained were evaluated by numerical simulations. The experimental performances of the sequences were tested by measurements carried out on a moderate sized protein at 750 MHz. The results presented demonstrate that the approach adopted in this study can be employed effectively to tailor, as per the experimental requirements and constraints, the RF-field modulation profiles of the pulses constituting the mixing scheme for generating heteronuclear J cross-polarisation sequences.

S100A1 binds to the calmodulin-binding site of ryanodine receptor and modulates skeletal muscle excitation-contraction coupling

S100A1, a 21-kDa dimeric Ca2+-binding protein, is an enhancer of cardiac Ca2+ release and contractility and a potential therapeutic agent for the treatment of cardiomyopathy. The role of S100A1 in skeletal muscle has been less well defined. Additionally, the precise molecular mechanism underlying S100A1 modulation of sarcoplasmic reticulum Ca2+ release in striated muscle has not been fully elucidated. Here, utilizing a genetic approach to knock out S100A1, we demonstrate a direct physiological role of S100A1 in excitation-contraction coupling in skeletal muscle. We show that the absence of S100A1 leads to decreased global myoplasmic Ca2+ transients following electrical excitation. Using high speed confocal microscopy, we demonstrate with high temporal resolution depressed activation of sarcoplasmic reticulum Ca2+ release in S100A1-/- muscle fibers. Through competition assays with sarcoplasmic reticulum vesicles and through tryptophan fluorescence experiments, we also identify a novel S100A1-binding site on the cytoplasmic face of the intact ryanodine receptor that is conserved throughout striated muscle and corresponds to a previously identified calmodulin-binding site. Using a 12-mer peptide of this putative binding domain, we demonstrate low micromolar binding affinity to S100A1. NMR spectroscopy reveals this peptide binds within the Ca2+-dependent hydrophobic pocket of S100A1. Taken together, these data suggest that S100A1 plays a significant role in skeletal muscle excitation-contraction coupling, primarily through specific interactions with a conserved binding domain of the ryanodine receptor. This warrants further investigation into the use of S100A1 as a therapeutic target for the treatment of both cardiac and skeletal myopathies.

Spin state selective Hadamard encoding during transfer periods using multiple selective CW-HCP

Hadamard spectroscopy today represents an alternative to conventional Fourier transform spectroscopy. The selective inversion of several narrow frequency bands is typically achieved by taylored inversion pulses in place of t1-evolution periods. However, band-selective inversion can also be achieved during coherence transfer steps, thereby shortening the period during which the magnetization is in the transverse plane. Using CW heteronuclear cross polarization (CW-HCP) as an example for highly selective coherence transfer, the implementation of Hadamard encoding within a transfer step is presented. Transfer characteristics, the preparation of multiple frequency selective CW-HCP and the possibility of acquiring spin state selective spectra are discussed in detail. The theoretical results are verified on two examples involving a cyclic pentapeptide and ubiquitin.

Spin state selectivity and heteronuclear Hartmann-Hahn transfer

Spin state selectivity can be obtained if inphase and antiphase magnetization can be transformed into each other. Heteronuclear Hartmann-Hahn transfer is usually used for the transfer of inphase magnetization. For a two spin system, however, a building block can be constructed that transfers inphase into antiphase magnetization and vice versa. The article gives a detailed description of the building block as well as experiments with elements similar to spin state selective coherence transfer (S(3)CT) and spin state selective excitation (S(3)E). The possibility of 'sensitivity enhancement' is pointed out and an application in the double selective measurement of coupling constants using a combination of CW-cross-polarization and the S(3)CT-type approach is demonstrated.

Transverse magnetization transfer under planar mixing conditions in spin systems consisting of three coupled spins 1/2

Polarization transfer under planar mixing conditions is a widely used tool in modern NMR-experiments. In the case of two coupled spins 1/2 or a chain of three or more spins 1/2 with only nearest neighbor couplings, it is only possible to transfer a single magnetization component (longitudinal magnetization in the principle axis system of the planar coupling tensors). However, if all couplings in a three-spin system are non-zero, it turns out that all magnetization components can be efficiently transferred even under strictly planar mixing conditions. In this article a detailed theoretical analysis is presented based on analytical transverse coherence transfer functions and on the underlying commutator algebra. In addition, transverse magnetization transfer is demonstrated experimentally. The results show that in highly coupled spin systems, as for example in the case of partially aligned samples with many residual dipolar couplings, special care has to be taken to avoid phase distortions if planar mixing steps are used.

Chemical shift anisotropy and offset effects in cross polarization solid-state NMR spectroscopy

The effect of an offset term in the cross-polarization (CP) Hamiltonian of a heteronuclear spin-12 pair due to off-resonant radio frequency (rf) irradiation and/or chemical shift anisotropy on one of the rf channels is investigated. Analytical solutions, simulations, and experimental results are presented. Formulating the CP spin dynamics in terms of an explicit unitary evolution operator enables the CP period to be inserted as a module in a given pulse scheme regardless of the initial density matrix present. The outcome of post-CP manipulation via pulses can be calculated on the resulting density matrix as the phases and amplitudes of all coherence modes are available. Using these tools it is shown that the offset can be used to reduce the rf power on that channel and the performance is further improved by a post-CP pulse whose flip angle matches and compensates the tilt of the effective field on the offset channel. Experimental investigations on single crystalline and polycrystalline samples of peptides confirm the oscillatory nature of CP dynamics and prove the slowing down of the dynamics under offset and/or mismatch conditions.

Broadband heteronuclear Hartmann-Hahn sequences with short cycle times

For some applications, broadband heteronuclear Hartmann-Hahn sequences with very short cycle times are required. A quality factor is presented that makes it possible to assess the relative sizes of cycle time, bandwidth, and maximum RF amplitude for any given multiple-pulse sequence. This quality factor is determined for multiple-pulse sequences that are commonly used in HEHAHA experiments and for some favorable sequences that were so far only discussed in the context of heteronuclear decoupling.

Analytical Polarization and Coherence Transfer Functions for Three Coupled Spins 1/2 under Planar Mixing Conditions

Analytical polarization and coherence transfer functions are presented for spin systems consisting of three spins 1/2 with arbitrary coupling constants under planar mixing conditions. In addition, simplified transfer functions were derived for symmetric coupling topologies. Based on these transfer functions optimal durations for the mixing period can be determined for correlations of interest. Copyright 1998 Academic Press. Copyright 1998 Academic Press