Andreas, L.B., et al., Dynamic Nuclear Polarization Study of Inhibitor Binding to the M218-60 Proton Transporter from Influenza A. Biochemistry, 2013.
We demonstrate the use of dynamic nuclear polarization (DNP) to elucidate ligand binding to a membrane protein using dipolar recoupling magic angle spinning (MAS) NMR. In particular, we detect drug binding in the proton transporter M218-60 from influenza A using recoupling experiments at room temperature and with cryogenic DNP. The results indicate that the pore binding site of rimantadine is correlated with previously reported widespread chemical shift changes, suggesting functional binding in the pore. Furthermore, the 15N labeled ammonium of rimantadine was observed near A30 13Cbeta and G34 13Calpha suggesting a possible hydrogen bond to A30 Carbonyl. Cryogenic DNP was required to observe the weaker external binding site(s) in a ZF-TEDOR spectrum. This approach is generally applicable, particularly for weakly bound ligands, in which case the application of MAS NMR dipolar recoupling requires the low temperatures to quench dynamic exchange processes. For the fully protonated samples investigated, we observed DNP signal enhancements of ~10 at 400 MHz using only 4-6 mM of the polarizing agent TOTAPOL. At 600 MHz/395 GHz and with DNP, we measured a distance between the drug and the protein to a precision of 0.2 A.