Mechanistic studies on shikimate pathway enzymes

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Enzymes can accelerate chemical reactions by more than a million-fold.  We are interested in understanding how amino acid residues within enzymes bring about this rate acceleration.  Some residues are involved in binding, others participate in the chemistry of the reaction, while other groups are involved in both. Our main focus is on enzymes involved in the biosynthesis of tyrosine. The enzymes under study, a mutase and a dehydrogenase, catalyze two consecutive reactions in this  pathway.  In some organisms, the reactions are catalyzed on separate polypeptides while in other bacteria, including E. coli the enzyme belongs to a special class called bifunctional proteins; two reactions are catalyzed on a single polypeptide.  We are interested in understanding how each of these enzyme-catalyzed reactions work separately, as well as delineating the relationship between the two activities.   In order to gain further information about one of the reactions in particular, we have recently solved the structure of a monofunctional dehydrogenase from a hyperthermophilic bacterium.  This structure is used to guide mutagenesis studies to probe the enzyme's mechanism of action and mode of regulation by tyrosine. Comparison of results with analogous studies on the bifunctional enzyme, for which there is no structure, help us gain insight into the interdependence of the two sites. The reactions catalyzed by these enzymes are specific to plants and microoganisms.  Knowledge of how specific enzymic residues bind to inhibitors could lead to the design of improved herbicides and antimicrobial agents.