Long‐range 19 F 15 N distance measurements in highly‐ 13 C, 15 N‐enriched solid proteins with 19 F‐dephased REDOR shift (FRESH) spectroscopy

We present a novel rotational‐echo double resonance (REDOR) method for detection of multiple 19 F 15 N distances in solid proteins. The method is applicable to protein samples containing a single 19 F label, in addition to high levels of 13 C and 15 N enrichment. REDOR dephasing pulses are applied on the 19 F channel during an indirect constant time chemical shift evolution period on 15 N, and polarization is then transferred to 13 C for detection, with high‐power 1 H decoupling throughout the sequence. This four‐channel experiment reports site‐specifically on 19 F 15 N distances, with highly accurate determinations of ∼5 Å distances and detection of correlations arising from internuclear distances of at least 8 Å. We demonstrate the method on the well‐characterized 56‐residue model protein GB1, where the sole tryptophan residue (Trp‐43) has been labeled with 5‐ 19 F‐Trp, in a bacterial growth medium also including 13 C‐glucose and 15 N ammonium chloride. In GB1, 11 distances are determined, all agreeing within 20% of the X‐ray structure distances. We envision the experiment will be utilized to measure quantitative long‐range distances for protein structure determination. Copyright © 2007 John Wiley & Sons, Ltd.