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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >NH3-dependent NAD+ synthetase from Bacillus subtilis at 1 A resolution.
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NH3-dependent NAD+ synthetase from Bacillus subtilis at 1 A resolution.

机译：从芽孢杆菌NH3-dependent NAD +合成酶细小的决议。

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摘要

The final step of NAD+ biosynthesis includes an amide transfer to nicotinic acid adenine dinucleotide (NaAD) catalyzed by NAD+ synthetase. This enzyme was co-crystallized in microgravity with natural substrates NaAD and ATP at pH 8.5. The crystal was exposed to ammonium ions, synchrotron diffraction data were collected and the atomic model was refined anisotropically at 1 A resolution to R = 11.63%. Both binding sites are occupied by the NAD-adenylate intermediate, pyrophosphate and two magnesium ions. The atomic resolution of the structure allows better definition of non-planar peptide groups, reveals a low mean anisotropy of protein and substrate atoms and indicates the H-atom positions of the phosphoester group of the reaction intermediate. The phosphoester group is protonated at the carbonyl O atom O7N, suggesting a carbenium-ion structure stabilized by interactions with two solvent sites presumably occupied by ammonia and a water molecule. A mechanism is proposed for the second catalytic step, which includes a nucleophilic attack by the ammonia molecule on the intermediate.
机译：NAD +生物合成的最后一步包括酰胺转移到烟酸腺嘌呤二核苷酸(NaAD)通过NAD +合成酶催化。这种酶在微重力co-crystallized与自然基质NaAD和ATP pH值8.5。水晶被暴露在铵离子,同步加速器衍射数据收集和原子模型精炼anisotropically在1一项决议R = 11.63%。被NAD-adenylate中间,焦磷酸和两个镁离子。解决结构允许更好non-planar肽组的定义,揭示了低的意思是各向异性的蛋白质和衬底原子和指示的氢原子,位置phosphoester组反应的中间。phosphoester组是质子化了的羰基O原子O7N,表明碳正离子通过交互有两个结构稳定溶剂的网站可能被氨和占领一个水分子。第二催化步骤,其中包括一个氨分子亲核攻击的中间。

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