PDF(Pubmed)
Abstract：
Allosteric regulation of inosine 5\'-monophosphate dehydrogenase (IMPDH), an essential enzyme of purine metabolism, contributes to the homeostasis of adenine and guanine nucleotides. However, the precise molecular mechanism of IMPDH regulation in bacteria remains unclear. Using biochemical and cryo-EM approaches, we reveal the intricate molecular mechanism of the IMPDH allosteric regulation in mycobacteria. The enzyme is inhibited by both GTP and (p)ppGpp, which bind to the regulatory CBS domains and, via interactions with basic residues in hinge regions, lock the catalytic core domains in a compressed conformation. This results in occlusion of inosine monophosphate (IMP) substrate binding to the active site and, ultimately, inhibition of the enzyme. The GTP and (p)ppGpp allosteric effectors bind to their dedicated sites but stabilize the compressed octamer by a common mechanism. Inhibition is relieved by the competitive displacement of GTP or (p)ppGpp by ATP allowing IMP-induced enzyme expansion. The structural knowledge and mechanistic understanding presented here open up new possibilities for the development of allosteric inhibitors with antibacterial potential.
摘要：
肌苷5'-单磷酸脱氢酶（IMPDH）的变构调节，嘌呤代谢的重要酶,有助于腺嘌呤和鸟嘌呤核苷酸的稳态。然而,细菌中IMPDH调控的确切分子机制尚不清楚。使用生化和低温EM方法，我们揭示了分枝杆菌中IMPDH变构调节的复杂分子机制。该酶被GTP和（p）ppGpp抑制，绑定到监管CBS域，通过与铰链区的碱性残基相互作用，将催化核心域锁定在压缩构象中。这导致与活性位点结合的肌苷一磷酸（IMP）底物的闭塞，最终,抑制酶。GTP和(p)ppGpp变构效应子结合到它们的专用位点,但通过共同机制稳定压缩的八聚体。通过ATP对GTP或(p)ppGpp的竞争性置换来缓解抑制,从而允许IMP诱导的酶扩增。这里介绍的结构知识和机理理解为开发具有抗菌潜力的变构抑制剂开辟了新的可能性。
