Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Biochemistry, Biophysics and Molecular Biology

First Advisor

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,

Copyright Owner

Kyung Hyun Kim



Proquest ID


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File Size

184 pages