Repetitive cross-polarization contacts via equilibration-re-equilibration of the proton bath: Sensitivity enhancement for NMR of membrane proteins reconstituted in magnetically aligned bicelles

• Published in: Journal of magnetic resonance (1997) Vol. 212; no. 1; pp. 245 - 248
• Main Authors: Tang, Wenxing, Nevzorov, Alexander A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2011
• Subjects: Algorithms; Bacteriophage Pf1 - chemistry; Cross-polarization; Electromagnetic Fields; Membrane proteins; Membrane Proteins - chemistry; Multiple contacts; Nuclear Magnetic Resonance, Biomolecular - methods; Protons; Sensitivity enhancement; Signal-To-Noise Ratio; Solid-state NMR; Spin temperature; Thermodynamics; Solid-state NMR; Spin temperature; Cross-polarization; Sensitivity enhancement; Multiple contacts; Membrane proteins
• ISSN: 1090-7807; 1096-0856; 1096-0856
• DOI: 10.1016/j.jmr.2011.06.028

[Display omitted] ► Cross-polarization (CP) cannot be fully transferred in a single contact for membrane proteins refolded in bicelles. ► This is due to thermodynamic and quantum mechanical bounds, as well as Hartmann-Hahn mismatches. ► The new REP-CP sequence yields a twofold gain for bicelle-reconstituted proteins as compared to a single CP. ► The gain is achieved by employing the differences between T 1 relaxation times for the high and low spins. Thermodynamic limit of magnetization corresponding to the intact proton bath usually cannot be transferred in a single cross-polarization contact. This is mainly due to the finite ratio between the number densities of the high- and low-gamma nuclei, quantum–mechanical bounds on spin dynamics, and Hartmann–Hahn mismatches due to rf field inhomogeneity. Moreover, for fully hydrated membrane proteins refolded in magnetically oriented bicelles, short spin-lock relaxation times ( T 1 ρ ) and rf heating can further decrease cross polarization efficiency. Here we show that multiple equilibrations-re-equilibrations of the high- and low-spin reservoirs during the preparation period yield an over twofold gain in the magnetization transfer as compared to a single-contact cross polarization (CP), and up to 45% enhancement as compared to the mismatch-optimized CP-MOIST scheme for bicelle-reconstituted membrane proteins. This enhancement is achieved by employing the differences between the spin–lattice relaxation times for the high- and low-gamma spins. The new technique is applicable to systems with short T 1 ρ ’s, and speeds up acquisition of the multidimensional solid-state NMR spectra of oriented membrane proteins for their subsequent structural and dynamic studies.