Enzyme Structure-Function Relationships

本文提出了两种方法来研究T4噬菌体二氢叶酸还原酶（T4 DHFR）和柠檬酸合酶（CS）两种不同酶与配体结合亲和力的结构-功能关系和催化机制。首先是对酶的结构进行晶体学分析，比较这些结构的配体亲和力和催化活性，并进一步与已知的远亲或突变形式的酶的结构进行比较。第二种方法将涉及研究静电场在这些酶中的作用。二氢叶酸还原酶催化DNA合成所必需的循环途径中的反应。特别是，它对合成叶酸化合物的抑制非常敏感，表现出很高的物种选择性。这些化合物对控制快速分裂的细胞具有重要意义。柠檬酸合成酶催化草酰乙酸和乙酰辅酶A缩合形成柠檬酸和辅酶A，是少数几种能够直接形成碳-碳键的酶之一。它提供了一个前所未有的机会来研究一个不寻常的机制，可能涉及顺序构象变化和静电不稳定的底物

Two approaches are proposed to investigate the structure-function relationships responsible for ligand binding affinities and catalytic mechanisms of two different enzymes, T4 bacteriophage dihydrofolate reductase (T4 DHFR) and citrate synthase (CS). The first will be a crystallographic analysis of the structures of the enzymes, a comparison of these structures in terms of ligand affinities and catalytic activity and a further comparison with known structures of distantly related or mutant forms of the enzymes. The second approach will involve an investigation of the role of electrostatic fields in these enzymes. Dihydrofolate reductase catalyzes a reaction in a cyclic pathway essential to DNA synthesis. In particular, it is highly susceptible to inhibition by synthetic folate compounds, showing high species selectivity. These compounds are of considerable interest for the control of rapidly dividing cells. Citrate synthase catalyzes the condensation of oxaloacetate and acetylCoenzyme A to form citrate and Coenzyme A. It is one of a few enzymes capable of directly forming a carbon-carbon bond. It presents an unprecedented opportunity to examine an unusual mechanism which probably involves sequential conformational changes and electrostatic destabilization of substrate.***//