DNP enhanced frequency-selective TEDOR experiments in bacteriorhodopsin

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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- 13C γ– 15N ε region in [U- 13C, 15N]-bacteriorhodopsin. We resolve six of the seven cross-peaks expected based on the primary sequence of this membrane protein.