Site-specific protein methyl deuterium quadrupolar patterns by proton-detected 3D 2H-13C-1H MAS NMR spectroscopy

Site-specific protein backbone deuterium 2Hα quadrupolar patterns by proton-detected quadruple-resonance 3D 2HαcαNH MAS NMR spectroscopy

A novel deuterium-excited and proton-detected quadruple-resonance three-dimensional (3D) ²H_αc_αNH MAS nuclear magnetic resonance (NMR) method is presented to obtain site-specific ²H_α deuterium quadrupolar couplings from protein backbone, as an extension to the 2D version of the experiment reported earlier. Proton-detection results in high sensitivity compared to the heteronuclei detection methods. Utilizing four independent radiofrequency (RF) channels (quadruple-resonance), we managed to excite the ²H_α, then transfer deuterium polarization to its attached C_α, followed by polarization transfers to the neighboring backbone nitrogen and then to the amide proton for detection. This experiment results in an easy to interpret HSQC-like 2D ¹H-¹⁵N fingerprint NMR spectrum, which contains site-specific deuterium quadrupolar patterns in the indirect third dimension. Provided that four-channel NMR probe technology is available, the setup of the ²H_αc_αNH experiment is relatively straightforward, by using low power deuterium excitation and polarization transfer schemes we have been developing. To our knowledge, this is the first demonstration of a quadruple-resonance MAS NMR experiment to link ²H_α quadrupolar couplings to proton-detection, extending our previous triple-resonance demonstrations. Distortion-free excitation and polarization transfer of ∼160-170 kHz ²H_α quadrupolar coupling were presented by using a deuterium RF strength of ∼20 kHz. From these ²H_α patterns, an average backbone order parameter of S = 0.92 was determined on a deuterated SH3 sample, with an average η = 0.22. These indicate that SH3 backbone represents sizable dynamics in the microsecond timescale where the ²H_α lineshape is sensitive. Moreover, site-specific ²H_α T₁ relaxation times were obtained for a proof of concept. This 3D ²H_αc_αNH NMR experiment has the potential to determine structure and dynamics of perdeuterated proteins by utilizing deuterium as a novel reporter.

Enhance Hydrogen Isotopes Separation by Alkali Earth Metal Dopant in Metal-Organic Framework

Kinetic quantum sieving (KQS) based on pore size and chemical affinity quantum sieving (CAQS) based on adsorption site are two routes of porous materials to separate hydrogen isotope mixtures. Alkali earth metals (Be, Mg, and Ca) were doped into UiO-67 to explore whether these metal sites can promote H₂/D₂ separation. Based on the zero-point energy and adsorption enthalpy calculated by density functional theory calculations, the Be dopant shows better H₂/D₂ separation performance than other alkali earth metal dopants and unsaturated metal sites in metal-organic frameworks based on CAQS. Orbital interaction strongly relates to the chemical affinity and further influences the D₂/H₂ selectivity. Moreover, the predicted D₂/H₂ selectivity of Be-doped sites (49.4) at 77 K is even larger than the best experimental result (26). Finally, the different dynamic behaviors of H₂ and D₂ on Be-doped UiO-67 indicate its strong H₂/D₂ separation performance via KQS.

How does it really move? Recent progress in the investigation of protein nanosecond dynamics by NMR and simulation

Nuclear magnetic resonance (NMR) spin relaxation experiments currently probe molecular motions on timescales from picoseconds to nanoseconds. The detailed interpretation of these motions in atomic detail benefits from complementarity with the results from molecular dynamics (MD) simulations. In this mini-review, we describe the recent developments in experimental techniques to study the backbone dynamics from ¹⁵N relaxation and side-chain dynamics from ¹³C relaxation, discuss the different analysis approaches from model-free to dynamics detectors, and highlight the many ways that NMR relaxation experiments and MD simulations can be used together to improve the interpretation and gain insights into protein dynamics.