The 2.8Angstrom RESOLUTION STRUCTURE OF THE ANTITUMOR PROTEIN NEOCARZINOSTATIN (NCS) will be extended to 2.0Angstrom resolution by structure factor calculations from the atom positions located in the 2.8Angstrom electron density map making use of the revised amino acid sequence. Refinement of the model of the structure will be done as the resolution is extended in order to precisely determine the structure of the protein molecule and improve the density where the chromophore resides in the holoprotein. Diffraction data (in hand) from crystals of apoNCS (2.2Angstrom will be used in comparison studies in attempting to understand how the chromophore binds and how it is stabilized by the protein. Structural studies of auromomycin and (macromomycin) will be initiated using diffraction data collected from auromomycin crystals. The molecule of NCS (or actinoxanthin) will be used as a starting model in the molecular replacement technique for beginning the structure analysis of AUR. I propose to begin a survey of DNA intercalating agents and small molecular weight anticancer agents for binding to the apoNCS chromophore binding-site for studying these associations as a function of binding coefficients and drug delivery to the cell. The main goal of these crystallographic studies is to obtain structural information which can be used in determining why the protein is so stable, what is characteristic about the molecule that makes it associate with the cell membrane, what residues in the cleft are directly involved in binding and/or protecting the very labile cofactor. The different antibiotic proteins will be compared for features likely responsible for their varying reactivities toward cells and DNA.
