Precision in the determination of the 3D structures of proteins by NMR depends on obtaining an adequate number of NOE restraints. Ambiguity in the assignment of NOE cross peaks between aromatic and other protons is an impediment to high quality structure determination. Two pulse sequences, 3D Haro-NOESY-CH3NH and 3D Caro-NOESY-CH3NH, based on a modification of a technique for simultaneous detection of 13C-1H (of CH3) and 15N-1H correlations in one measurement, are proposed in the present work. These 3D experiments, which are optimized for resolution in the 13C and 15N dimensions, provide NOE information between aromatic protons and methyl or amide protons. CH2 moieties are filtered out and the CH groups in aromatic rings are selected, allowing their NOE cross peaks to be unambiguously assigned. Unambiguous NOEs connecting aromatic and methyl or amide protons will provide important restraints for protein structure calculations.
Bibliographical noteFunding Information:
This work was supported in part by grants to G.Z. from the Research Grants Council of Hong Kong (HKUST6038/98M, 6199/99M and 6208/00M). The Hong Kong Biotechnology Research Institute is acknowledged for the purchase of the 750 MHz NMR spectrometer. The authors thank Dr. K.H. Sze and Dr. David Smith for their kind help and valuable discussions.