Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Biochemistry, Biophysics and Molecular Biology

First Advisor

Mark Hargrove

Second Advisor

Drena Dobbs


Hemoglobins are ancient proteins that predate the divergence of prokaryotes and eukaryotes. Although the most thoroughly studied hemoglobins are mammalian oxygen transporters, it has become clear that this function is a recent evolutionary advancement coinciding with the "oxygen revolution" and the development of multicellular organisms. Hemoglobins capable of oxygen transport are highly specialized structurally to maintain pentacoordination of the heme and appropriate ligand rate and equilibrium constants, while preventing autooxidation due to bound oxygen. Their predecessors however, adopt a more energetically favorable hexacoordinate conformation that precludes oxygen transport;Despite the fact that hexacoordinate hemoglobins are ubiquitous in biological organisms, little is known about their purpose and mechanisms of function. Endogenous reversible hexacoordination in these proteins raises questions about the structural arrangements that must occur within the protein for exogenous ligand binding to occur. The goal of this research is to increase the body of knowledge about ligand binding in hexacoordinate hemoglobins by examining both their global structural accommodation of ligands and the role of specific residues in regulating ligand affinity. This research has focused specifically on the truncated hemoglobin from Synechocystis and on the nonsymbiotic hemoglobins from rice and barley;Synechocystis hemoglobin was chosen because it combines several unique characteristics that set it apart from other truncated and hexacoordinate proteins. This work explores the structural characterization of endogenously hexacoordinate Synechocystis hemoglobin by x-ray crystallography, the structural conformation changes that take place in this protein upon exogenous ligand binding, and the function of the unique covalent bond found between the heme and a non-axial histidine within the protein. Hemoglobins from rice and barley are the common model proteins for study within the plant non-symbiotic hemoglobin group. This work examines the effect of the mutation of a key residue in hexacoordinate rice hemoglobin, the effect of exogenous ligand binding on barley hemoglobin, and the structural changes necessary for the evolution of oxygen transport in plant hemoglobins.



Digital Repository @ Iowa State University,

Copyright Owner

Julie Anne Hoy



Proquest ID


File Format


File Size

159 pages

Included in

Biophysics Commons