M. tuberculosis harbors an essential phosphoserine phosphatase (MtSerB2, Rv3042c) that contains two small- molecule binding ACT-domains (Pfam 01842) at the N-terminus followed by the phosphoserine phosphatase (PSP) domain. We found that exogenously added MtSerB2 elicits microtubule rearrangements in THP-1 cells. Mutational analysis demonstrates that phosphatase activity is co-related to the elicited rearrangements, while addition of the ACT-domains alone elicits no rearrangements. The enzyme is dimeric, exhibits divalent metal- ion dependency, and is more specific for l- phosphoserine unlike other classical PSPases. Binding of a variety of amino acids to the ACT-domains influences MtSerB2 activity by either acting as activators/inhibitors/have no effects. Additionally, reduced activity of the PSP domain can be enhanced by equimolar addition of the ACT domains. Further, we identified that G18 and G108 of the respective ACT-domains are necessary for ligand-binding and their mutations to G18A and G108A abolish the binding of ligands like l- serine. A specific transition to higher order oligomers is observed upon the addition of l- serine at ∼0.8 molar ratio as supported by Isothermal calorimetry and Size exclusion chromatography experiments. Mutational analysis shows that the transition is dependent on binding of l- serine to the ACT-domains. Furthermore, the higher-order oligomeric form of MtSerB2 is inactive, suggesting that its formation is a mechanism for feedback control of enzyme activity. Inhibition studies involving over eight inhibitors, MtSerB2, and the PSP domain respectively, suggests that targeting the ACT-domains can be an effective strategy for the development of inhibitors.
结核杆菌携带一种重要的
磷酸丝氨酸磷酸酶(MtSerB2,Rv3042c),它在 N 端含有两个小分子结合 ACT 域(Pfam 01842),其后是
磷酸丝氨酸磷酸酶(P
SP)域。我们发现,外源添加的 MtSerB2 会引起 THP-1 细胞中微管的重排。突变分析表明,
磷酸酶活性与引起的重排有共同关系,而单独添加 ACT 域则不会引起重排。该酶是二聚体,表现出对二价
金属离子的依赖性,而且与其他经典
磷酸化酶不同,它对 l-
磷酸丝氨酸更具特异性。多种
氨基酸与 ACT 域的结合会影响 MtSerB2 的活性,既可能是激活剂,也可能是
抑制剂,还可能没有任何影响。此外,等摩尔添加 ACT 结构域可增强 P
SP 结构域降低的活性。此外,我们还发现各自 ACT 结构域中的 G18 和 G108 是
配体结合所必需的,它们突变为 G18A 和 G108A 后,
配体(如 l-
丝氨酸)的结合就会消失。等温量热法和尺寸排阻色谱法实验证明,当加入摩尔比为 0.8 的 l-
丝氨酸时,可以观察到向高阶低聚物的特定转变。突变分析表明,这种转变取决于 l-
丝氨酸与 ACT 结构域的结合。此外,MtSerB2 的高阶寡聚形式没有活性,这表明它的形成是酶活性的一种反馈控制机制。分别涉及超过八种
抑制剂、MtSerB2 和 P
SP 结构域的抑制研究表明,靶向 ACT-结构域是开发
抑制剂的有效策略。