Celikel Reha, Veldore Vidya Harini, Mathews Irimpan, Devine Kevin M, Varughese Kottayil I
Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, 4301 West Markham Street, Little Rock, AR 72205, USA.
Acta Crystallogr D Biol Crystallogr. 2012 Jul;68(Pt 7):839-45. doi: 10.1107/S090744491201373X. Epub 2012 Jun 15.
In Bacillus subtilis, the WalRK (YycFG) two-component system coordinates murein synthesis with cell division. It regulates the expression of autolysins that function in cell-wall remodeling and of proteins that modulate autolysin activity. The transcription factor WalR is activated upon phosphorylation by the histidine kinase WalK, a multi-domain homodimer. It autophosphorylates one of its histidine residues by transferring the γ-phosphate from ATP bound to its ATP-binding domain. Here, the high-resolution crystal structure of the ATP-binding domain of WalK in complex with ATP is presented at 1.61 Å resolution. The bound ATP remains intact in the crystal lattice. It appears that the strong binding interactions and the nature of the binding pocket contribute to its stability. The triphosphate moiety of ATP wraps around an Mg(2+) ion, providing three O atoms for coordination in a near-ideal octahedral geometry. The ATP molecule also makes strong interactions with the protein. In addition, there is a short contact between the exocyclic O3' of the sugar ring and O2B of the β-phosphate, implying an internal hydrogen bond. The stability of the WalK-ATP complex in the crystal lattice suggests that such a complex may exist in vivo poised for initiation of signal transmission. This feature may therefore be part of the sensing mechanism by which the WalRK two-component system is so rapidly activated when cells encounter conditions conducive for growth.
在枯草芽孢杆菌中，WalRK（YycFG）双组分系统协调胞壁质合成与细胞分裂。它调控在细胞壁重塑中起作用的自溶素以及调节自溶素活性的蛋白质的表达。转录因子WalR在被组氨酸激酶WalK磷酸化后被激活，WalK是一种多结构域同型二聚体。它通过将结合在其ATP结合结构域上的ATP的γ-磷酸基团转移到自身的一个组氨酸残基上而实现自身磷酸化。在此，展示了WalK的ATP结合结构域与ATP复合物的高分辨率晶体结构，分辨率为1.61 Å。结合的ATP在晶格中保持完整。看来强结合相互作用和结合口袋的性质有助于其稳定性。ATP的三磷酸基团环绕着一个Mg(2+)离子，提供三个O原子以近乎理想的八面体几何构型进行配位。ATP分子也与蛋白质形成强相互作用。此外，糖环的外环O3'与β-磷酸的O2B之间存在短接触，这意味着存在一个分子内氢键。WalK - ATP复合物在晶格中的稳定性表明这种复合物可能在体内以准备启动信号传递的状态存在。因此，这一特征可能是当细胞遇到有利于生长的条件时WalRK双组分系统能如此快速被激活的传感机制的一部分。
