Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.
BMC Microbiol. 2012 Jul 8;12:136. doi: 10.1186/1471-2180-12-136.
PII proteins have a fundamental role in the control of nitrogen metabolism in bacteria, through interactions with different PII targets, controlled by metabolite binding and post-translational modification, uridylylation in most organisms. In the photosynthetic bacterium Rhodospirillum rubrum, the PII proteins GlnB and GlnJ were shown, in spite of their high degree of similarity, to have different requirements for post-translational uridylylation, with respect to the divalent cations, Mg(2+) and Mn(2+).
Given the importance of uridylylation in the functional interactions of PII proteins, we have hypothesized that the difference in the divalent cation requirement for the uridylylation is related to efficient binding of Mg/Mn-ATP to the PII proteins. We concluded that the amino acids at positions 42 and 85 in GlnJ and GlnB (in the vicinity of the ATP binding site) influence the divalent cation requirement for uridylylation catalyzed by GlnD.
Efficient binding of Mg/Mn-ATP to the PII proteins is required for uridylylation by GlnD. Our results show that by simply exchanging two amino acid residues, we could modulate the divalent cation requirement in the uridylylation of GlnJ and GlnB.Considering that post-translational uridylylation of PII proteins modulates their signaling properties, a different requirement for divalent cations in the modification of GlnB and GlnJ adds an extra regulatory layer to the already intricate control of PII function.
PII 蛋白在细菌的氮代谢控制中起着基础性作用，通过与不同 PII 靶标的相互作用来实现，这些靶标受代谢物结合和翻译后修饰（在大多数生物体中为尿苷酰化）的控制。在光合细菌红螺菌中，尽管 GlnB 和 GlnJ 蛋白具有高度相似性，但它们在后翻译尿苷酰化方面对二价阳离子 Mg(2+)和 Mn(2+)的需求不同。
鉴于尿苷酰化在 PII 蛋白功能相互作用中的重要性，我们假设尿苷酰化中二价阳离子需求的差异与 PII 蛋白与 Mg/Mn-ATP 的有效结合有关。我们得出结论，GlnJ 和 GlnB 中第 42 位和第 85 位的氨基酸（靠近 ATP 结合位点）影响 GlnD 催化的尿苷酰化的二价阳离子需求。
GlnD 进行尿苷酰化需要 PII 蛋白与 Mg/Mn-ATP 的有效结合。我们的结果表明，只需交换两个氨基酸残基，就可以调节 GlnJ 和 GlnB 尿苷酰化中二价阳离子的需求。考虑到 PII 蛋白的翻译后尿苷酰化调节它们的信号转导特性，GlnB 和 GlnJ 修饰中二价阳离子需求的不同为 PII 功能的复杂调控增加了一个额外的调节层。
