Refinement and Comparisons of the Structures of DAHPsynthases and KDOPsynthase

3-脱氧-D-阿拉伯-庚酮糖酸-7-磷酸合酶（DAHP合酶）和3-脱氧-D-甘露-辛酮糖酸-8-磷酸合酶（KDOP合酶）的结构将通过X射线晶体学在原子分辨率下单独测定和与底物、抑制剂和调节剂复合测定。这些酶共有19%的序列同一性，并且具有彼此相似的二级结构。 这些酶在使用金属离子和通过反馈抑制进行调节方面有所不同。因此，这些研究的最终目标是确定这些酶之间的相似性和可能的同源性。 这些酶催化磷酸烯醇丙酮酸与分别含有四个（赤藓糖-4-磷酸）和五个（阿拉伯糖-5-磷酸）碳的糖分子的缩合。 在这两种情况下，发生不寻常的裂解，因为磷酸烯醇丙酮酸的碳-氧键被裂解，而不是氧-磷键。 这两种酶都处于生物合成途径的重要点，一种导致芳香族终产物，另一种导致革兰氏阴性菌外膜的脂多糖。 通过X射线晶体学进行结构研究的总体目标是了解这两种酶的底物结合和作用机制的相似性和差异，以及这两种酶是同源物还是通过趋同进化而产生的。 ***

9723633 Kretsinger The structures of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPsynthase) and 3-deoxy-D-manno-octulosonate-8-phosphate synthase (KDOPsynthase), will be determined by X-ray crystallography at atomic resolution, alone and in complex with substrates, inhibitors and regulators. The enzymes share 19% sequence identity and have secondary structures that resemble one another. The enzymes differ in their use of metal ions and regulation by feedback inhibition. Thus the ultimate goal of these studies is to determine the similarities and possible homologies between these enzymes. These enzymes catalyze the condensation of phosphoenol pyruvate with a sugar molecule containing four (erythrose-4-phosphate) and five (arabinose-5-phosphate) carbons, respectively. In both cases, an unusual cleavage occurs, in that the carbon-oxygen bond of phosphoenol pyruvate is cleaved and not the oxygen-phosphorus bond. Both enzymes are at important points of a biosynthetic pathway, one leading to aromatic end products, the other leading to the lipopolysaccharide of the outer membrane in Gram negative bacteria. The overall goal of this structural investigation by X-ray crystallography is to understand the similarities and differences in substrate binding and mechanisms of action of these two enzymes, and whether these two enzymes are homologues or have arisen by convergent evolution. ***