Acetylation Coordinates the Crosstalk between Carbon Metabolism and Ammonium Assimilation

Enteric bacteria use up to 15% of their cellular energy for ammonium assimilation via glutamine synthetase (GS)/glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH), in response to low or high ammonium availability. However, the sensory mechanisms for effective and appropriate coordination between carbon metabolism and ammonium assimilation are not fully elucidated. Here, we report that, in Salmonella, carbon metabolism coordinates the activities of GS/GDH via functional reversible protein lysine acetylation. Glucose simultaneously promotes acetyltransferase Pat-mediated acetylation on Lys164 and Lys353 of GS to activate the adenylylated-GS by inducing its conformation change, while on Lys128 of GDH to inactivate the enzyme by impeding its catalytic center, respectively, which are reversed by deacetylase CobB-mediated deacetylation. Molecular dynamic (MD) simulations indicated that the acetylation activation of GS activity was adenylylation-dependent. Acetylation and deacetylation occur within minutes of ‘glucose shock’ to promptly adapt to ammonium/carbon variation and finely balance glutamine/glutamate synthesis. Acetylation can rehabilitate the growth tardiness of Salmonella mutant with chromosomal mimetic mutation of adenylylated-GS and thus help its survival in mice. Thus, glucose-driven acetylation integrates the signals of assimilation and carbon metabolism for proper growth control.

肠道细菌可利用高达15%的细胞能量，通过谷氨酰胺合成酶（glutamine synthetase，GS）/谷氨酸合酶（glutamate synthase，GOGAT）与谷氨酸脱氢酶（glutamate dehydrogenase，GDH）通路完成铵同化，以适配不同浓度的铵离子可利用水平。然而，碳代谢与铵同化之间实现有效且精准协调的感知机制尚未完全明晰。本研究发现，在沙门氏菌（Salmonella）中，碳代谢可通过功能性可逆蛋白质赖氨酸乙酰化调控GS与GDH的活性。葡萄糖可同时介导两类乙酰化修饰：一方面促进乙酰转移酶Pat（acetyltransferase Pat）催化谷氨酰胺合成酶Lys164与Lys353位点发生乙酰化，通过诱导其构象变化激活腺苷酸化谷氨酰胺合成酶（adenylylated-GS）；另一方面催化谷氨酸脱氢酶Lys128位点乙酰化，通过阻碍其催化中心使该酶失活。上述两种乙酰化修饰均可被去乙酰化酶CobB（deacetylase CobB）介导的去乙酰化作用逆转。分子动力学（Molecular dynamic，MD）模拟结果显示，谷氨酰胺合成酶活性的乙酰化激活依赖于腺苷酸化修饰。乙酰化与去乙酰化可在“葡萄糖冲击”发生数分钟内完成，从而快速响应铵/碳源的变化，并精细平衡谷氨酰胺与谷氨酸的合成进程。乙酰化修饰可修复携带腺苷酸化谷氨酰胺合成酶染色体模拟突变的沙门氏菌的生长迟缓表型，助力其在小鼠体内定植存活。综上，葡萄糖驱动的乙酰化信号通路可整合铵同化与碳代谢的调控信号，实现精准的生长控制。