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Molecular Rationale for Improved Dynamic Nuclear Polarization of Biomembranes
journal contribution
posted on 2016-07-19, 00:00 authored by Adam N. Smith, Umar T. Twahir, Thierry Dubroca, Gail E. Fanucci, Joanna R. LongDynamic nuclear polarization (DNP)
enhanced solid-state NMR can
provide orders of magnitude in signal enhancement. One of the most
important aspects of obtaining efficient DNP enhancements is the optimization
of the paramagnetic polarization agents used. To date, the most utilized
polarization agents are nitroxide biradicals. However, the efficiency
of these polarization agents is diminished when used with samples
other than small molecule model compounds. We recently demonstrated
the effectiveness of nitroxide labeled lipids as polarization agents
for lipids and a membrane embedded peptide. Here, we systematically
characterize, via electron paramagnetic (EPR), the dynamics of and
the dipolar couplings between nitroxide labeled lipids under conditions
relevant to DNP applications. Complemented by DNP enhanced solid-state
NMR measurements at 600 MHz/395 GHz, a molecular rationale for the
efficiency of nitroxide labeled lipids as DNP polarization agents
is developed. Specifically, optimal DNP enhancements are obtained
when the nitroxide moiety is attached to the lipid choline headgroup
and local nitroxide concentrations yield an average e––e– dipolar coupling of 47 MHz. On the basis
of these measurements, we propose a framework for development of DNP
polarization agents optimal for membrane protein structure determination.