Proton evolved local field solid-state nuclear magnetic resonance using Hadamard encoding: Theory and application to membrane proteins

Abstract

NMR anisotropic parameters such as dipolar couplings and chemical shifts are central to structure and orientation determination of aligned membrane proteins and liquid crystals. Among the separated local field experiments, the proton evolved local field (PELF) scheme is particularly suitable to measure dynamically averaged dipolar couplings and give information on local molecular motions. However, the PELF experiment requires the acquisition of several 2D datasets at different mixing times to optimize the sensitivity for the complete range of dipolar couplings of the resonances in the spectrum. Here, we propose a new PELF experiment that takes the advantage of the Hadamard encoding (HE) to obtain higher sensitivity for a broad range of dipolar couplings using a single 2D experiment. The HE scheme is obtained by selecting the spin operators with phase switching of hard pulses. This approach enables one to detect four spin operators, simultaneously, which can be processed into two 2D spectra covering a broader range of dipolar couplings. The advantages of the new approach are illustrated for a U-15 N NAL single crystal and the U-15 N labeled single-pass membrane protein sarcolipin reconstituted in oriented lipid bicelles. The HE-PELF scheme can be implemented in other multidimensional experiments to speed up the characterization of the structure and dynamics of oriented membrane proteins and liquid crystalline samples.

Time-shared experiments for efficient assignment of triple-selectively labeled proteins

“…A pictorial representation of this Hadamard decoding scheme [56, 87, 88] applied to the ts-HN(CO)/HN(CA) experiment is provided in Fig. 2a.…”

Orphan spin operators enable the acquisition of multiple 2D and 3D magic angle spinning solid-state NMR spectra

“…In static ss-NMR, we designed POE to recover chemical shift or dipolar coupling coherences and convert them into observable terms to enhance the sensitivity of heteronuclear correlations (HET-COR) or separated local field experiments such as PISEMA (polarization inversion spin exchange at magic angle). [5][6][7][8]21 We also developed the DUMAS approach, 9, 10 which consists of using SIM-CP between 1 H, 13 C, and 15 N to store and utilize 15 N magnetization, thus obtaining the simultaneous acquisition of two 2D experiments. Moreover, we discovered the possibility of transferring the magnetization simultaneously between 15 N and 13 Cα (or 13 C ) and vice versa for the acquisition of two 3D experiments concurrently.…”

“…While in liquid-state NMR there are several pulse sequences designed to detect discarded coherences via dual receivers or phase cycling schemes, 4 in ssNMR there are only a few examples that utilize orphan (i.e., neglected) spin operators to boost sensitivity. [5][6][7][8][9][10][11][12][13] In general, classical ssNMR pulse sequences eliminate orphan spin operators of magnetization either using z-filters or phase cycling schemes that suppress the spectral artifacts arising from undesired coherence transfer pathways.…”

“…[5][6][7][8] For rotating solids, we developed the dual acquisition magic angle spina) Author to whom correspondence should be addressed. Electronic mail:…”

Solid-state Hadamard NMR spectroscopy: Simultaneous measurements of multiple selective homonuclear scalar couplings

“…This intriguing approach has revealed attractive features over the conventional Fourier transform NMR spectroscopy such as, exclusion of undesired spectral regions / data-sampling, significant reduction in experimental time as well as an enhancement in signal to noise ratio by a factor √2. On the other hand, the power and utility of the Hadamard encoding is only rarely explored in solid-state NMR, such as dipolar assisted rotational resonance (DARR) [30], saturation in deuterated solids [31] and proton local field [32] experiments. Herein, we adopt the Hadamard encoding strategy for selective refocusing instead of excitations in solid-state NMR, and exemplify for accurate measurement of 1 J CC and 3 J CC in uniformly 13 C-labelled Histidine.HCl.…”