Microbial Metabolism Research Group, Max Planck Institute for Marine Microbiology, Celsiusstraße 1, 28359, Bremen, Germany.
Department of Microbiology, Radboud Institute for Biological and Environmental Sciences, Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.
Commun Biol. 2024 Jan 19;7(1):111. doi: 10.1038/s42003-023-05726-w.
Glutamine synthetases (GS) catalyze the ATP-dependent ammonium assimilation, the initial step of nitrogen acquisition that must be under tight control to fit cellular needs. While their catalytic mechanisms and regulations are well-characterized in bacteria and eukaryotes, only limited knowledge exists in archaea. Here, we solved two archaeal GS structures and unveiled unexpected differences in their regulatory mechanisms. GS from Methanothermococcus thermolithotrophicus is inactive in its resting state and switched on by 2-oxoglutarate, a sensor of cellular nitrogen deficiency. The enzyme activation overlays remarkably well with the reported cellular concentration for 2-oxoglutarate. Its binding to an allosteric pocket reconfigures the active site through long-range conformational changes. The homolog from Methermicoccus shengliensis does not harbor the 2-oxoglutarate binding motif and, consequently, is 2-oxoglutarate insensitive. Instead, it is directly feedback-inhibited through glutamine recognition by the catalytic Asp50'-loop, a mechanism common to bacterial homologs, but absent in M. thermolithotrophicus due to residue substitution. Analyses of residue conservation in archaeal GS suggest that both regulations are widespread and not mutually exclusive. While the effectors and their binding sites are surprisingly different, the molecular mechanisms underlying their mode of action on GS activity operate on the same molecular determinants in the active site.
谷氨酰胺合成酶（GS）催化 ATP 依赖性铵同化，这是氮获取的初始步骤，必须严格控制以适应细胞的需求。尽管它们的催化机制和调节在细菌和真核生物中得到了很好的描述，但在古菌中只有有限的知识。在这里，我们解决了两个古菌 GS 的结构，并揭示了它们在调节机制上的意外差异。产热甲烷球菌的 GS 在其静止状态下无活性，而被 2-氧戊二酸激活，2-氧戊二酸是细胞氮缺乏的传感器。酶的激活与报道的细胞 2-氧戊二酸浓度非常吻合。它与别构口袋的结合通过远程构象变化重新配置活性位点。来自圣地亚古球菌的同源物不含有 2-氧戊二酸结合基序，因此对 2-氧戊二酸不敏感。相反，它通过催化天冬氨酸 50′-环对谷氨酰胺的识别直接受到反馈抑制，这种机制在细菌同源物中很常见，但在产热甲烷球菌中由于残基取代而不存在。对古菌 GS 中残基保守性的分析表明，这两种调节方式都很普遍，并不相互排斥。虽然效应物及其结合位点惊人地不同，但它们对 GS 活性作用模式的分子机制在活性位点上基于相同的分子决定因素起作用。
