Allostery refers to the process in which interaction of an effector ligand with one site of the protein changes the function of the protein at a distant site. Despite the critical role of allostery in regulation of metabolic pathways, little is known about the details of the allosteric networks and the remarkable diversity in allosteric mechanisms. This study utilises several examples of allosteric proteins to illustrate the interwoven relationships between various allosteric mechanisms, ranging from large conformational changes to subtle dynamic communications. An important metabolic enzyme, 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAH7PS), was selected for this study due to its unique diversity of allosteric regulations and its important role as the first committed step in aromatic amino acid biosynthesis. Essential in many pathogenic bacteria, however lacking mammalian counterparts, DAH7PS and related pathway enzymes provide opportunities in development of novel antimicrobial drugs.

The first part of this study addresses the determinants of allosteric ligand selectivity and potency for DAH7PS enzymes that exhibit large conformational changes, and provides structural and functional insights that contribute to the understanding of the role of conformational change in allostery. The second part of this study addresses interchangeability between two different allosteric mechanisms by demonstrating the ease of gene fusion to link two contemporary protein domains and produce functional chimera. The third part of this study addresses the allosteric regulation in DAH7PS enzymes from a different subfamily, for which no large conformational changes are involved in delivering allosteric communication. The crystal structure of a related chorismate mutase enzyme contributes to the understanding of protein-protein interactions associated with allosteric regulations employed by this type of DAH7PS. The final part of this study addresses the current limitations in studying allosteric systems and explores the advantages of new techniques, including Förster resonance energy transfer and electron paramagnetic resonance, in offering valuable information on the timescales and molecular structures associated with allostery.