Biomolecular Interaction Centre, Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand.
J Mol Biol. 2013 May 13;425(9):1582-92. doi: 10.1016/j.jmb.2012.12.019. Epub 2012 Dec 28.
3-Deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAH7PS) catalyzes the first step in the shikimate pathway, the pathway responsible for the biosynthesis of the aromatic amino acids Trp, Phe, and Tyr. Unlike many other organisms that produce up to three isozymes, each feedback-regulated by one of the aromatic amino acid pathway end products, Mycobacterium tuberculosis expresses a single DAH7PS enzyme that can be controlled by combinations of aromatic amino acids. This study shows that the synergistic inhibition of this enzyme by a combination of Trp and Phe can be significantly augmented by the addition of Tyr. We used X-ray crystallography, mutagenesis, and isothermal titration calorimetry studies to show that DAH7PS from M. tuberculosis possesses a Tyr-selective site in addition to the Trp and Phe sites, revealing an unusual and highly sophisticated network of three synergistic allosteric sites on one enzyme. This ternary inhibitory response, by a combination of all three aromatic amino acids, allows a tunable response of the protein to changing metabolic demands.
3-脱氧-D-阿拉伯庚酮糖-7-磷酸合酶（DAH7PS）催化莽草酸途径的第一步，该途径负责芳香族氨基酸色氨酸、苯丙氨酸和酪氨酸的生物合成。与许多产生多达三种同工酶的其他生物体不同，每个同工酶都受到芳香族氨基酸途径终产物之一的反馈调节，结核分枝杆菌表达一种单一的 DAH7PS 酶，可通过芳香族氨基酸的组合进行控制。这项研究表明，色氨酸和苯丙氨酸的组合对该酶的协同抑制作用可以通过添加酪氨酸显著增强。我们使用 X 射线晶体学、突变和等温热滴定法研究表明，结核分枝杆菌的 DAH7PS 除了具有色氨酸和苯丙氨酸结合位点外，还具有一个酪氨酸结合位点，揭示了一种在一种酶上具有三个协同变构位点的不寻常且高度复杂的网络。这种由三种芳香族氨基酸组成的三元抑制反应允许该蛋白对代谢需求的变化做出可调节的反应。
