Biotin Protein Ligase (BPL) is an essential enzyme responsible for the covalent attachment of biotin to a specific lysine residue of biotin-dependent carboxylases, transcarboxylases and decarboxylases. Due to the fundamental processes that these enzymes are involved in such as lipogenesis, amino acid catabolism and gluconeogenesis, much research has been conducted on these enzymes. Studies encompassing structural, mutational and catalytic functions of these enzymes have lead to novel drug developments for the treatment of obesity, diabetes, metabolic syndrome, bacterial and fungal infections. As BPL is required for activation of these enzymes by biotinylation, it is believed that it too could be targeted in a similar way to produce novel therapeutics. To date, the most characterised BPLs are from the Gramnegative bacteria Escherichia coli and the archea Pyrococcus hirokoshii. However minimal information is known about other forms of clinically important bacterial species or eukaryotic forms of this important enzyme. Through my candidature I have compiled a thorough literature review summarised as chapter 1: Introduction. Furthering this literature analysis, a human BPL model was generated with aid of BPL structural co-ordinates already deposited in the protein data bank (PDB), thus allowing focus on human BPL mutations that cause multiple carboxylase deficiency (chapter 2). I have solved the structure of BPL from the clinically important pathogenic bacteria Staphylococcus aureus. This was performed in several ligand-bound and non-bound states (chapters 3 and 4). A novel high-throughput assay was developed to test BPL activity. This assay allow testing of compounds that could potentially inhibit the BPL from Candida albicans (a species responsible for invasive fungal infections) (chapter 5). Large amounts of highly purified BPL from Saccharomyces cerevisiae allowed for the first structural analysis of a eukaryotic BPL (Chapter 6). The work has been summarised by a general discussion and future directions for the project (Chapter 7). / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2009