Dihydrodipicolinate synthase (DHDPS) from Campylobacter jejuni is a natively homotetrameric enzyme that catalyzes the first unique reaction of (S)-lysine biosynthesis and is feedback-regulated by lysine through binding to an allosteric site. High-resolution structures of the DHDPS-lysine complex have revealed significant insights into the binding events. One key asparagine residue, N84, makes hydrogen bonds with both the carboxyl and the α-amino group of the bound lysine. We generated two mutants, N84A and N84D, to study the effects of these changes on the allosteric site properties. However, under normal assay conditions, N84A displayed notably lower catalytic activity, and N84D showed no activity. Here we show that these mutations disrupt the quaternary structure of DHDPS in a concentration-dependent fashion, as demonstrated by size-exclusion chromatography, multi-angle light scattering, dynamic light scattering, small-angle X-ray scattering (SAXS) and high-resolution protein crystallography.

中文翻译：

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天冬酰胺84，一种调节性的变构位点残基，有助于维持空肠弯曲杆菌双氢二吡啶甲酸合酶的四级结构。

空肠弯曲杆菌的二氢二吡啶甲酸合酶（DHDPS）是天然的同源四聚酶，它催化（S）-赖氨酸生物合成的第一个独特反应，并通过与变构位点结合而由赖氨酸反馈调节。DHDPS-赖氨酸复合物的高分辨率结构揭示了对结合事件的重要见解。一个关键的天冬酰胺残基N84与结合的赖氨酸的羧基和α-氨基都形成氢键。我们生成了两个突变体N84A和N84D，以研究这些变化对变构位点性质的影响。但是，在正常测定条件下，N84A表现出明显较低的催化活性，而N84D没有表现出活性。在这里，我们证明了这些突变以浓度依赖性的方式破坏了DHDPS的四级结构，