PMID- 25965279 OWN - NLM STAT- MEDLINE DCOM- 20160314 LR - 20170728 IS - 1096-0856 (Electronic) IS - 1090-7807 (Linking) VI - 256 DP - 2015 Jul TI - Optimization of cross-polarization at low radiofrequency fields for sensitivity enhancement in solid-state NMR of membrane proteins reconstituted in magnetically aligned bicelles. PG - 14-22 LID - S1090-7807(15)00092-0 [pii] LID - 10.1016/j.jmr.2015.03.016 [doi] AB - Solid-state NMR (ssNMR) of oriented membrane proteins (MPs) is capable of providing structural and dynamic information at nearly physiological conditions. However, NMR experiments performed on oriented membrane proteins generally suffer from low sensitivity. Moreover, utilization of high-power radiofrequency (RF) irradiations for magnetization transfer may give rise to sample heating, thereby decreasing the efficiency of conventional cross-polarization schemes. Here we have optimized the recently developed repetitive cross-polarization (REP-CP) sequence (Tang et al., 2011) to further increase the magnetization transfer efficiency for membrane proteins reconstituted in magnetically aligned bicelles and compared its performance to single-contact Hartmann-Hahn cross-polarization (CP), CP-MOIST and the adiabatic transfer. It has been found that employing the REP-CP sequence at RF amplitudes of 19kHz instead of the commonly used higher RF fields (>45kHz) enhances the efficiency of REP-CP. An additional 30% signal can be obtained as compared to the previously published REP-CP, and 20% when compared to the re-optimized REP-CP at 50kHz RF fields. Moreover, the (15)N signal gain of low-power REP-CP was found to be 40% over the adiabatic CP and up to 80% over CP-MOIST. Thus, the low-power REP-CP sequence surpasses all of the previous CP schemes in addition of having the tremendous advantage of reducing the RF powers by a factor of seven, thereby preserving the liquid-like bicelle sample. By contrast, in purely static (NAL crystal) and semi-rigid systems (Pf1 phage), the adiabatic CP was found to be more effective. Periodic oscillations of the intensity profile (distinct from the transient oscillations) as a function of the CP contact time and B1 RF field strengths were observed during the REP-CP optimization with the oscillations becoming more pronounced with lower RF fields. Many-spin simulations were performed to explain the oscillations and their periodicity. CI - Copyright (c) 2015 Elsevier Inc. All rights reserved. FAU - Koroloff, Sophie N AU - Koroloff SN AD - Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695-8204, USA. FAU - Nevzorov, Alexander A AU - Nevzorov AA AD - Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, NC 27695-8204, USA. Electronic address: alex_nevzorov@ncsu.edu. LA - eng PT - Journal Article PT - Research Support, U.S. Gov't, Non-P.H.S. DEP - 20150428 PL - United States TA - J Magn Reson JT - Journal of magnetic resonance (San Diego, Calif. : 1997) JID - 9707935 RN - 0 (Lipid Bilayers) RN - 0 (Membrane Proteins) SB - IM MH - *Algorithms MH - Computer Simulation MH - Lipid Bilayers/*chemistry MH - Magnetic Fields MH - Magnetic Resonance Spectroscopy/*methods MH - Membrane Proteins/*chemistry/radiation effects/*ultrastructure MH - *Models, Chemical MH - Models, Molecular MH - Protein Conformation MH - Radio Waves MH - Reproducibility of Results MH - Sensitivity and Specificity OTO - NOTNLM OT - Low RF powers OT - Membrane proteins OT - Multiple CP contacts OT - Oriented samples OT - Repetitive cross-polarization (REP-CP) OT - Sensitivity enhancement OT - Solid-state NMR EDAT- 2015/05/13 06:00 MHDA- 2016/03/15 06:00 CRDT- 2015/05/13 06:00 PHST- 2015/01/23 00:00 [received] PHST- 2015/03/10 00:00 [revised] PHST- 2015/03/15 00:00 [accepted] PHST- 2015/05/13 06:00 [entrez] PHST- 2015/05/13 06:00 [pubmed] PHST- 2016/03/15 06:00 [medline] AID - S1090-7807(15)00092-0 [pii] AID - 10.1016/j.jmr.2015.03.016 [doi] PST - ppublish SO - J Magn Reson. 2015 Jul;256:14-22. doi: 10.1016/j.jmr.2015.03.016. Epub 2015 Apr 28.