Date of Award
Doctor of Philosophy
Biochemistry, Biophysics and Molecular Biology
Richard B. Honzatko
The crystal structure of adenylosuccinate synthetase from Eschericha coli has been pursued to a resolution of 3.7 A. Using isomorphous and anomalous (SIRAS) phases from a HgI[subscript]4[superscript]2- derivative, electron density maps were generated that clearly revealed the envelope of the enzyme dimer and the two-fold molecular symmetry of the dimer;Since the enzyme is active as a dimer consisting of two identical monomers, the method of density averaging (Bricogne, 1976) was employed to improve the electron density map based on SIRAS phases. The non-crystallographic two-fold operator, which relates two monomers, was refined against an SIRAS electron density map of 4.0 A resolution. The molecular two-fold axis was found about 10° away from the direction perpendicular to the crystallographic two-fold screw axis, significantly different from its previous location (Serra, 1990);The polypeptide conformation from the N terminus to the C terminus was traced in the averaged electron density map at 3.7 A resolution. Although there were some regions of discontinuous density, particularly at the surface of the enzyme, secondary structures were recognizable. On the basis of the assigned positions of the N and the C terminus and sequence homology to other mononucleotide binding proteins, the tentative binding sites for mononucleotides and succinate were determined;Reference. Bricogne, G. J. Mol. Biol. 1976, A32, 832-847. Serra, M. A. Ph.D. Dissertation, Iowa State University, 1990.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Kyung Hyun Kim
Kim, Kyung Hyun, "The crystal structure of adenylosuccinate synthetase from Escherichia coli " (1990). Retrospective Theses and Dissertations. 9518.