Sensitivity and resolution enhancement of oriented solid-state NMR: application to membrane proteins

Abstract

Oriented solid-state NMR (O-ssNMR) spectroscopy is a major technique for the high-resolution analysis of the structure and topology of transmembrane proteins in native-like environments. Unlike magic angle spinning (MAS) techniques, O-ssNMR spectroscopy requires membrane protein preparations that are uniformly oriented (mechanically or magnetically) so that anisotropic NMR parameters, such as dipolar and chemical shift interactions, can be measured to determine structure and orientation of membrane proteins in lipid bilayers. Traditional sample preparations involving mechanically aligned lipids often result in short relaxation times which broaden the (15)N resonances and encumber the manipulation of nuclear spin coherences. The introduction of lipid bicelles as membrane mimicking systems has changed this scenario, and the more favorable relaxation properties of membrane protein (15)N and (13)C resonances make it possible to develop new, more elaborate pulse sequences for higher spectral resolution and sensitivity. Here, we describe our recent progress in the optimization of O-ssNMR pulse sequences. We explain the theory behind these experiments, demonstrate their application to small and medium size proteins, and describe the technical details for setting up these new experiments on the new generation of NMR spectrometers.

Keywords: 4-pentyl-4′-cyanobiphenyl; 5CB; BLEW; Burum Linser Ernst Windowless; CP; CSA; Chemical shift anisotropy; DC; DTRF; Dipolar couplings; FSLG; Frequency-Switched Lee-Goldberg; HETCOR; HIMSELF; Heteronuclear Isotropic Mixing Separated Local Field; LG; Lee-Goldberg; MAS; MLEV; MSHOT; Magic Sandwich Higher Order Truncation; Malcolm Levitt Decoupling Sequence; N-acetyl-leucine; N-acetyl-valine-leucine; NAL; NAVL; O-ssNMR; Oriented solid-state NMR; PDSD; PELF; PI; PISEMA; PLN; Proton Evolved Local Field; RMS; Resolution enhancement; SAMPI4; SE; SLN; SNR; Sarcolipin; Selective Averaging Magic Sandwich with Polarization Inversion; Sensitivity enhancement; WIM24; Windowless Isotropic Mixing 24; chemical shift anisotropy; cross polarization; dipolar coupling; doubly tilted rotating frame; heteronuclear correlation; magic angle spinning; oriented solid-state NMR; phospholamban; polarization inversion; polarization inversion spin exchange at the magic angle; proton driven spin diffusion; root mean square; sensitivity enhancement; signal to noise ratio.