Mechanistic studies on shikimate pathway enzymes

酶可以将化学反应加速一百万倍以上。 我们感兴趣的是了解酶中的氨基酸残基是如何导致这种速率加速的。 一些残基参与结合，其他残基参与反应的化学过程，而其他基团则参与两者。我们的主要重点是参与酪氨酸生物合成的酶。正在研究的酶，一种脱氢酶和一种脱氢酶，催化这一途径中的两个连续反应。 在某些生物体中，这些反应是在单独的多肽上催化的，而在其他细菌中，包括大肠杆菌。这种酶属于一类特殊的双功能蛋白质，在一个多肽上催化两种反应。 我们有兴趣了解这些酶催化反应中的每一个是如何单独工作的，以及描绘这两个活动之间的关系。 为了获得关于其中一个反应的进一步信息，我们最近解决了来自超嗜热细菌的单功能脱氢酶的结构。 该结构用于指导诱变研究，以探测酶的作用机制和酪氨酸调节模式。比较结果与类似的研究双功能酶，其中没有结构，帮助我们深入了解这两个网站的相互依赖性。这些酶催化的反应是植物和微生物特有的。 了解特定的酶残基如何与抑制剂结合，可以设计出改进的除草剂和抗菌剂。

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.