NUCLEAR MAGNETIC RESONANCE--NEW METHODS AND MOLECULAR STRUCTURE DETERMINATION

偶极偶联对于有a的分子不会平均为零

Dipolar couplings do not average to zero for molecules with a significant magnetic susceptibility anisotropy. Such dipolar couplings to have been measured for the GATA1-DNA binding domain, complexed with a 16-basepair fragment of DNA. Addition of dipolar coupling constraints was shown to result in a considerable improvement in the quality of the structure and to allow, for the first time, positioning of elements of the protein that are connected by long range NOE interactions. Magnetic field dependence of the nuclear resonance frequencies was observed for the first time in solution NMR, and results obtained for the GATA1-DNA complex confirm the improvement in structural quality upon addition of the dipolar constraints. New methods were developed for measurement of 1H and 13C chemical shift anisotrphy (CSA). A correlation between amide proton CSA and hydrogen bond length was found by comparing 1HN CSA values in human ubiquitin with hydrogen bond lengths obtained from its X-ray crystal structure. The CSA tensor for 13Ca carbons was found to depend strongly on the polypeptide backbone angles, f and y, and measurement of the 13Ca CSA potentially could increase the quaity of protein structures significantly. Other newly developed methods for measurement of the backbone angles f show that the amide N-H bond, on average, makes an angle of less than 6o with the C'-N-Ca plane, confirming the high degree of planarity for peptide bonds and contradicting the results of theoretical calculations.