2H–13C correlation solid-state NMR for investigating dynamics and water accessibilities of proteins and carbohydrates

Abstract

Site-specific determination of molecular motion and water accessibility by indirect detection of H NMR spectra has advantages over dipolar-coupling based techniques due to the large quadrupolar couplings and the ensuing high angular resolution. Recently, a Rotor Echo Short Pulse IRrAdiaTION mediated cross polarization (CP) technique was developed, which allowed efficient transfer of H magnetization toC at moderate H radiofrequency field strengths available on most commercial MAS probes. In this work, we investigate theH-C magnetization transfer characteristics of one-bond perdeuterated CD spin systems and two-bond H/D exchanged C-(O)-D and C-(N)-D spin systems in carbohydrates and proteins. Our results show that multi-bond, broadbandH-C polarization transfer can be achieved using H radiofrequency fields of ~50 kHz, relatively short contact times of 1.3-1.7 ms, and with sufficiently high sensitivity to enable 2DH-C correlation experiments with undistorted H spectra in the indirect dimension. To demonstrate the utility of thisH-C technique for studying molecular motion, we show H-C correlation spectra of perdeuterated bacterial cellulose, whose surface glucan chains exhibit a motionally averaged C6 H quadrupolar coupling that indicates fast trans-gauche isomerization about the C5-C6 bond. In comparison, the interior chains in the microfibril core are fully immobilized. Application of theH-C correlation experiment to H/D exchanged Arabidopsis primary cell walls show that the O-D quadrupolar spectra of the highest polysaccharide peaks can be fit to a two-component model, in which 74% of the spectral intensity, assigned to cellulose, has a near-rigid-limit coupling, while 26% of the intensity, assigned to matrix polysaccharides, has a weakened coupling of 50 kHz. The latter O-D quadrupolar order parameter of 0.22 is significantly smaller than previously reported C-D dipolar order parameters of 0.46-0.55 for pectins, suggesting that additional motions exist at the C-O bonds in the wall polysaccharides. H-C polarization transfer profiles are also compared between statistically deuterated and H/D exchanged GB1.

Solid-state NMR spectroscopy

“…Many of these new pulse sequences are expected to capitalize on the increased resolution and coherence lifetimes enabled by faster MAS, higher magnetic fields and the increased polarization available from DNP. New methods to measure distances and large-amplitude motions under these high-field and fast-MAS conditions will be especially desirable 39,40 .…”

“…For the latter, acyl chain order parameters can be quantified in the absence and presence of proteins using chain-perdeuterated lipids 36,37 . Recently, 13 C and 15 N-detected 2 H MAS NMR experiments have been indirectly developed to study uniformly labelled proteins and carbohydrates to determine molecular motion in a site-resolved and multiplexed manner [38][39][40] .…”

Nanofluidic voidless electrode for electrochemical capacitance enhancement in gel electrolyte

“…This analysis identifies three modes of free (3 kHz), intermediate (33 kHz), and surface-bound (135 kHz) interlayer D 2 O in the deuterated particles (Fig. 1d ) 27 , 28 . The bound D 2 O (135 kHz) is static and has hydrogen bonding with the functional groups on the channel surface 29 .…”

Pulsed Third-Spin-Assisted Recoupling NMR for Obtaining Long-Range 13C–13C and 15N–13C Distance Restraints

“…All experiments were carried out under 20 kHz MAS. Microcrystalline GB1 samples were expressed and purified as previously described [35][36] . Glucagon peptide was purchased from Biopeptek Pharmaceuticals (Malvern, PA) and fibrillized in pH 2 solution at 21˚C for 7 days at a concentration of 8 mg/ml 37 .…”