Xu Y, Carr P D, Huber T, Vasudevan S G, Ollis D L
Center for Molecular Structure and Function, Research School of Chemistry, Australian National University, Canberra, Australia.
Eur J Biochem. 2001 Apr;268(7):2028-37. doi: 10.1046/j.1432-1327.2001.02074.x.
PII is a signal transduction protein that is part of the cellular machinery used by many bacteria to regulate the activity of glutamine synthetase and the transcription of its gene. The structure of PII was solved using a hexagonal crystal form (form I). The more physiologically relevant form of PII is a complex with small molecule effectors. We describe the structure of PII with ATP obtained by analysis of two different crystal forms (forms II and III) that were obtained by co-crystallization of PII with ATP. Both structures have a disordered recognition (T) loop and show differences at their C termini. Comparison of these structures with the form I protein reveals changes that occur on binding ATP. Surprisingly, the structure of the PII/ATP complex differs with that of GlnK, a functional homologue. The two proteins bind the base and sugar of ATP in a similar manner but show differences in the way that they interact with the phosphates. The differences in structure could account for the differences in their activities, and these have been attributed to a difference in sequence at position 82. It has been demonstrated recently that PII and GlnK form functional heterotrimers in vivo. We construct models of the heterotrimers and examine the junction between the subunits.
PII是一种信号转导蛋白，是许多细菌用于调节谷氨酰胺合成酶活性及其基因转录的细胞机制的一部分。PII的结构是通过六方晶体形式（形式I）解析得到的。PII在生理上更相关的形式是与小分子效应物形成的复合物。我们通过分析PII与ATP共结晶得到的两种不同晶体形式（形式II和III）来描述PII与ATP的结构。这两种结构都有一个无序的识别（T）环，并且在它们的C末端显示出差异。将这些结构与形式I蛋白进行比较，揭示了结合ATP时发生的变化。令人惊讶的是，PII/ATP复合物的结构与功能性同源物GlnK的结构不同。这两种蛋白质以相似的方式结合ATP的碱基和糖，但在与磷酸相互作用的方式上显示出差异。结构上的差异可能解释了它们活性上的差异，这些差异归因于第82位的序列差异。最近已证明PII和GlnK在体内形成功能性异源三聚体。我们构建了异源三聚体的模型并检查了亚基之间的连接。
