NMR STUDIES OF BIOMOLECULAR STRUCTURE, FUNCTION, AND DYNAMICS

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The aims of this project are: (1) to develop and modify NMR methodologies for the assignment of resonances and the analysis of the structure and dynamics of molecules in solution, and (2) to apply these methods to problems of concern in relation to environmental health. During the past year, the main emphasis of this project has been on the development of the transferred NOE (TRNOE) technique and its application to the determination of the conformation of the nucleoside drug tubercidin in the complex with E. coli purine nucleoside phosphorylase (PNPase). Several methods were developed to analyze binding kinetics, and dissociation rate constants of 2400 s-1 and 1200 s-1 and 20xC and 10xC, respectively, were determined. Specific deuteration of the 2' position of the inhibitor tubercidin has been carried out in order to reduce or eliminate several important spin diffusion pathways in the inhibitor. Unexpectedly, bound tubercidin was found to correspond to two very different conformations: a major syn conformation and a minor, anticonformation. Ligand competition studies involving tubercidin and 9-deazainosine further suggest that both modes of binding involve interaction with the active sites of the enzyme. Other studies have continued to probe the interaction of benzeneboronic acid (BBA) derivatives with the serine protease subtilisin and with model ligands. In addition to these macromolecular studies, a new approach to editing 1H NMR spectra selectively based on the shifts of scalar coupled carbon-13 nuclei has been evaluated and applied to several model systems. Proton NMR studies were also carried out to determine the structure of corticosterone and deoxycorticosterone metabolites produced by mutated forms of cytochrome P450. A new initiative involving the use of NMR spectroscopy to study structural and conformational aspects of the human estrogen receptor has recently begun.