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

• Main Authors: O'Neill, Hugh (Author), Gelenter, Martin David (Contributor), Wang, Tuo (Contributor), Liao, Shu-Yu (Contributor), Hong, Mei (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Chemistry (Contributor)
• Format: Article
• Language: English
• Published: Springer Netherlands, 2018-07-20T20:09:50Z.
• Subjects: Article
• Online Access: Get fulltext

 Site-specific determination of molecular motion and water accessibility by indirect detection of [superscript 2]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 (RESPIRATION[subscript CP]) technique was developed, which allowed efficient transfer of [superscript 2]H magnetization to [superscript 13]C at moderate [superscript 2]H radiofrequency field strengths available on most commercial MAS probes. In this work, we investigate the [superscript 2]H-[superscript 13]C magnetization transfer characteristics of one-bond perdeuterated CD[subscript n] 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, broadband [superscript 2]H-[superscript 13]C polarization transfer can be achieved using 2H radiofrequency fields of ~50 kHz, relatively short contact times of 1.3-1.7 ms, and with sufficiently high sensitivity to enable D [superscript 2]H-[superscript 13]C correlation experiments with undistorted [superscript 2]H spectra in the indirect dimension. To demonstrate the utility of this [superscript 2]H-[superscript 13]C technique for studying molecular motion, we show [superscript 2]H-[superscript 13]C correlation spectra of perdeuterated bacterial cellulose, whose surface glucan chains exhibit a motionally averaged C6 2H 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 the [superscript 2]H-[superscript 13]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. [superscript 2]H-[superscript 13]C polarization transfer profiles are also compared between statistically deuterated and H/D exchanged GB1. Keywords: Molecular motion, RESPIRATION[subscript CP], Cellulose, Plant primary cell walls, Trans-gauche isomerization