Hamada Keisuke, Kato Masato, Shimizu Toshiyuki, Ihara Kentaro, Mizuno Takeshi, Hakoshima Toshio
Structural Biology Laboratory, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
Genes Cells. 2005 Jan;10(1):1-11. doi: 10.1111/j.1365-2443.2005.00817.x.
The multiple histidine-aspartate phosphorelay system plays a crucial role in cellular adaptation to environments in microorganisms and plants. Like kinase-phosphatase systems in higher eukaryotes, the multiple steps provide additional regulatory checkpoints with phosphatases. The Escherichia coli phosphatase SixA exhibits protein phosphatase activity against the histidine-containing phosphotransfer (HPt) domain located in the C-terminus of the histidine kinase ArcB engaged in anaerobic responses. We have determined the crystal structures of the free and tungstate-bound forms of SixA at 2.06 A and 1.90 A resolution, respectively. The results provide the first three-dimensional view of a bacterial protein histidine phosphatase, revealing a compact alpha/beta architecture related to a family of phosphatases containing the arginine-histidine-glycine (RHG) motif at their active sites. Compared with these RHG phosphatases, SixA lacks an extra alpha-helical subdomain as a lid over the active site, thereby forming a relatively shallow groove important for the accommodation of the HPt domain of ArcB. The tungstate ion, which mimics the substrate phosphate group, is located at the centre of the active site where the active residue, His8, points to the tungsten atom in the mode of in-line nucleophilic attack.
多组氨酸 - 天冬氨酸磷酸化中继系统在微生物和植物细胞适应环境过程中发挥着关键作用。与高等真核生物中的激酶 - 磷酸酶系统一样，多个步骤通过磷酸酶提供了额外的调控检查点。大肠杆菌磷酸酶SixA对参与厌氧反应的组氨酸激酶ArcB C末端含组氨酸的磷酸转移（HPt）结构域表现出蛋白磷酸酶活性。我们分别以2.06 Å和1.90 Å的分辨率测定了SixA游离形式和钨酸盐结合形式的晶体结构。结果首次提供了细菌蛋白组氨酸磷酸酶的三维视图，揭示了一种紧凑的α/β结构，与一类在其活性位点含有精氨酸 - 组氨酸 - 甘氨酸（RHG）基序的磷酸酶相关。与这些RHG磷酸酶相比，SixA在活性位点上方缺少一个额外的α - 螺旋亚结构域作为盖子，从而形成了一个相对较浅的凹槽，这对于容纳ArcB的HPt结构域很重要。模拟底物磷酸基团的钨酸根离子位于活性位点中心，活性残基His8以亲核攻击的方式指向钨原子。
