Carbon dioxide is an omnipresent gas that drives adaptive responses within organisms from all domains of life. The molecular mechanisms by which proteins serve as sensors of CO₂ are, accordingly, of great interest. Because CO₂ is electrophilic, one way it can modulate protein biochemistry is by carboxylation of the amine group of lysine residues. However, the resulting CO₂-carboxylated lysines spontaneously decompose, giving off CO₂, which makes studying this modification difficult. Here we describe a method to stably mimic CO₂-carboxylated lysine residues in proteins. We leverage this method to develop a quantitative approach to identify CO₂-carboxylated lysines of proteins and explore the lysine ‘carboxylome’ of the CO₂-responsive cyanobacterium Synechocystis sp. We uncover one CO₂-carboxylated lysine within the effector binding pocket of the metabolic signaling protein PII. CO₂-carboxylatation of this lysine markedly lowers the affinity of PII for its regulatory effector ligand ATP, illuminating a negative molecular control mechanism mediated by CO₂.

二氧化碳是一种无所不在的气体，可驱动生命各个领域的生物体内的适应性反应。因此，蛋白质作为 CO ₂传感器的分子机制引起了极大的兴趣。因为 CO ₂是亲电子的，所以它可以调节蛋白质生物化学的一种方式是通过赖氨酸残基的胺基的羧化作用。然而，由此产生的 CO ₂羧化赖氨酸会自发分解，释放出 CO ₂，​​这使得研究这种修饰变得困难。在这里，我们描述了一种稳定模拟蛋白质中 CO ₂ -羧化赖氨酸残基的方法。我们利用这种方法开发了一种定量方法来识别 CO ₂- 蛋白质的羧基化赖氨酸并探索 CO ₂响应性蓝藻Synechocystis sp. 的赖氨酸“羧基组”。我们在代谢信号蛋白 PII 的效应结合口袋中发现了一个 CO _{2 -羧化赖氨酸。}该赖氨酸的CO ₂羧化作用显着降低了 PII 对其调节效应配体 ATP 的亲和力，阐明了由 CO ₂介导的负分子控制机制。