DNP enhanced frequency-selective TEDOR experiments in bacteriorhodopsin

We describe a new approach to multiple 13C-15N distance measurements in uniformly labeled solids, frequency-selective (FS) TEDOR. The method shares features with FS-REDOR and ZF- and BASE-TEDOR, which also provide quantitative 15N-13C spectral assignments and distance measurements in U-[13C,15N] samples. To demonstrate the validity of the FS-TEDOR sequence, we measured distances in [U-13C,15N]-asparagine which are in good agreement with other methods. In addition, we integrate high frequency dynamic nuclear polarization (DNP) into the experimental protocol and use FS-TEDOR to record a resolved correlation spectrum of the Arg-13Cγ-15Nε region in [U-13C,15N]-bacteriorhodopsin. We resolve six of the seven cross-peaks expected based on the primary sequence of this membrane protein.