INTER-TRYPTOPHAN DISTANCES IN RAT CELLULAR RETINOL-BINDING PROTEIN II BY SOLID-STATE NMR

Structural constraints for the tryptophans in rat cellular retinol binding protein II (CRBP II) have been obtained by rotational-echo double-resonance (REDOR) solid-state NMR. CRBP II was labeled with L-[6-F-19]tryptophan and L-[2-C-13]tryptophan. The C-13-F-19 dipolar coupling was determined for various possible tryptophan geometries. The allowed distance between the closest two of the four tryptophans in CRBP II was obtained for each geometry. The minimum possible distance between these two tryptophans in CRBP II is 7 angstrom, and the maximum possible distance is 11 angstrom.