Modest Offset Difference Internuclear Selective Transfer via Homonuclear Dipolar Coupling

Abstract

Homonuclear dipolar recoupling is routinely used for magic-angle spinning NMR-based structure determination. In fully protonated samples, only short proton–proton distances are accessible to broadband recoupling approaches because of high proton density. Selective methods allow detection of longer distances by directing polarization to a subset of spins. Here we introduce the selective pulse sequence MODIST, which recouples spins that have a modest chemical shift offset difference, and demonstrate it to selectively record correlations between amide protons. The sequence was selected for good retention of total signal, leading to up to twice the intensity for proton–proton correlations compared with other selective methods. The sequence is effective across a range of spinning conditions and magnetic fields, here tested at 55.555 and 100 kHz magic-angle spinning and at proton Larmor frequencies from 600 to 1200 MHz. For influenza A M2 in lipid bilayers, cross-peaks characteristic of a helical conformation are observed.

1H-Detected Biomolecular NMR under Fast Magic-Angle Spinning

“…Inspired by SPR, jump return pulses of varying pulse widths and phase were simulated for a four-proton spin system modeled after two amide protons and two α protons. The performance was evaluated according to preservation of total signal and selective transfer among the amide protons, which resulted in the selection of the pulse sequence dubbed modest offset difference internuclear selective transfer (MODIST, Figure b) . The selectivity of the method was shown to be similar for both strong and weak couplings, with only a minor dependence on placement of the offset, such that both amide–amide and aliphatic-aliphatic transfers occur simultaneously.…”

Integrated Assessment of the Structure and Dynamics of Solid Proteins

“…The restraints are an order of magnitude more numerous than for deuterated proteins but are associated, as of now, with severe shortcomings regarding a quantitative interpretation, which compromises the value of established structure elucidation approaches. − In the solid state, for detailed elucidation of dynamic ensembles within crystalline proteins, supramolecular assemblies, fibrils, and membrane proteins, a similar impact of concatenation of experiment and simulation via the maximum-entropy principle can be expected as for solution NMR. However, due to the sparseness (e.g., isolated REDOR spin pairs) or rather qualitative character (e.g., current homonuclear recoupling techniques ,,,,− ) of distance restraints in magic-angle spinning solid-state NMR, prospects have been limited to chemical-shift anisotropy and dipolar coupling-based implementations in oriented membrane protein samples. , Opposing the limited perspectives prevailing for the large range of solid proteins, here we demonstrate integrated assessment of structure and dynamics via experimental data from fast MAS NMR, leveraged by a dense network of accurate proton–proton distances made attainable.…”

Great Offset Difference Internuclear Selective Transfer

“…We also acquired 2D experiments with three other selective methodsMODIST, DREAM, , and SPR5 4 pulses (Figure S7A)that show lower efficiency carbonyl–carbonyl correlations. Figure S7B shows GODIST efficiency at a 1200 MHz spectrometer.…”