NDLI: Efficient DNP NMR of membrane proteins: sample preparation protocols, sensitivity, and radical location

Content Provider	Springer Nature Link
Author	Liao, Shu Y. Lee, Myungwoon Wang, Tuo Sergeyev, Ivan V. Hong, Mei
Copyright Year	2016
Abstract	Although dynamic nuclear polarization (DNP) has dramatically enhanced solid-state NMR spectral sensitivities of many synthetic materials and some biological macromolecules, recent studies of membrane-protein DNP using exogenously doped paramagnetic radicals as polarizing agents have reported varied and sometimes surprisingly limited enhancement factors. This motivated us to carry out a systematic evaluation of sample preparation protocols for optimizing the sensitivity of DNP NMR spectra of membrane-bound peptides and proteins at cryogenic temperatures of ~110 K. We show that mixing the radical with the membrane by direct titration instead of centrifugation gives a significant boost to DNP enhancement. We quantify the relative sensitivity enhancement between AMUPol and TOTAPOL, two commonly used radicals, and between deuterated and protonated lipid membranes. AMUPol shows ~fourfold higher sensitivity enhancement than TOTAPOL, while deuterated lipid membrane does not give net higher sensitivity for the membrane peptides than protonated membrane. Overall, a ~100 fold enhancement between the microwave-on and microwave-off spectra can be achieved on lipid-rich membranes containing conformationally disordered peptides, and absolute sensitivity gains of 105–160 can be obtained between low-temperature DNP spectra and high-temperature non-DNP spectra. We also measured the paramagnetic relaxation enhancement of lipid signals by TOTAPOL and AMUPol, to determine the depths of these two radicals in the lipid bilayer. Our data indicate a bimodal distribution of both radicals, a surface-bound fraction and a membrane-bound fraction where the nitroxides lie at ~10 Å from the membrane surface. TOTAPOL appears to have a higher membrane-embedded fraction than AMUPol. These results should be useful for membrane-protein solid-state NMR studies under DNP conditions and provide insights into how biradicals interact with phospholipid membranes.
Starting Page	223
Ending Page	237
Page Count	15
File Format	PDF
ISSN	09252738
Journal	Journal of Biomolecular NMR
Volume Number	64
Issue Number	3
e-ISSN	15735001
Language	English
Publisher	Springer Netherlands
Publisher Date	2016-02-12
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Membrane proteins Sensitivity enhancement DNP Influenza M2 AMUPol Paramagnetic relaxation enhancement Solid-state NMR Biophysics and Biological Physics Biochemistry Spectroscopy/Spectrometry
Content Type	Text
Resource Type	Article
Subject	Spectroscopy Biochemistry

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