The thesis presented here describes the steps that were taken in an attempt to solve the protein structure of MenD via molecular replacement and multiple wavelength anomalous dispersion. The introduction provides background on menaquinone biosynthesis and the role of MenD in this metabolic pathway. Also, a detailed discussion of the DC Family of enzymes, a subgroup of ThDP dependent enzymes, which MenD is a part of, is included.<p> Utilizing various software packages a 1.9 Å data set was processed and analyzed in an attempt to provide a molecular replacement result. When molecular replacement was deemed incapable of solving the phase problem of the data set, the production of SeMet protein was attempted to allow for MAD phasing.<p> A homology model of MenD was produced using the program Modeller with benzaldehyde lyase as a template. A structure based sequence alignment was done with all DC Family enzymes with structures published. Then a second structure based sequence alignment was done to compare the same set to the Modeller model. This was done to gain a deeper understanding of MenD and how it interacts with its cofactors ThDP and Mg2+. Furthermore, these results were used to implicate potential active site residues.

The thesis presented here describes the steps that were taken in an attempt to solve the protein structure of MenD via molecular replacement and multiple wavelength anomalous dispersion. The introduction provides background on menaquinone biosynthesis and the role of MenD in this metabolic pathway. Also, a detailed discussion of the DC Family of enzymes, a subgroup of ThDP dependent enzymes, which MenD is a part of, is included.<p> Utilizing various software packages a 1.9 Å data set was processed and analyzed in an attempt to provide a molecular replacement result. When molecular replacement was deemed incapable of solving the phase problem of the data set, the production of SeMet protein was attempted to allow for MAD phasing.<p> A homology model of MenD was produced using the program Modeller with benzaldehyde lyase as a template. A structure based sequence alignment was done with all DC Family enzymes with structures published. Then a second structure based sequence alignment was done to compare the same set to the Modeller model. This was done to gain a deeper understanding of MenD and how it interacts with its cofactors ThDP and Mg2+. Furthermore, these results were used to implicate potential active site residues.

Indiana University-Purdue University Indianapolis (IUPUI) / Thiamin diphosphate (ThDP)-dependent enzymes catalyze a wide range of reactions including the oxidative and nonoxidative decarboxylation of 2-keto acids, carboligation reactions, the cleavage of C-C bonds, and the formation of C-S, C-N, and C-O bonds. Surprisingly, given this diversity, all ThDP-dependent enzyme catalyzed reactions proceed through essentially the same intermediate. This suggests that these enzymes share a common ancestry and have evolved to become the diverse group of enzymes seen today. Sequence alignments have revealed that all ThDP-dependent enzymes share two common ThDP binding domains, the PYR domain and the PP domain. In addition to these conserved domains, over time, other domains have been added creating further diversity in this superfamily. For instance, the TH3 domain, found in many ThDP-dependent enzymes, serves the function of binding additional cofactors such as FAD in enzymes like acetohydroxyacid synthase (AHAS) but in others, like pyruvate decarboxylase (PDC), it has lost this function completely. The work presented here focuses on ThDP-dependent decarboxylases. In this thesis, several evolutionary aspects of this group of enzymes will be examined including (i) the characterization of an evolutionary forerunner in the presence of a mechanism-based inhibitor, (ii) the characterization of the minor isozymes of pyruvate decarboxylase from Saccharomyces cerevisiae, and (iii) the development of a selection method to increase the efficiency of the site-saturation mutagenesis used to study ThDP-dependent enzyme evolution.

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