cKAT acetylation of the CO2 hydration protein ChpX regulates the CO2 concentrating mechanism in cyanobacteria.

Lysine acetylation (Kac) is a critical post-translational modification that regulates photosynthesis and carbon metabolism in cyanobacteria. However, the diversity and functional roles of lysine acetyltransferases (KATs) beyond the well-characterized cGNAT2 remain poorly defined. This study identifies and functionally characterizes the previously unannotated protein A0096, designated here as cKAT, demonstrating its capacity to catalyze Kac both in vivo and in vitro in Synechococcus sp. PCC 7002 (Synechococcus). Deletion of cKAT significantly impaired cellular growth and photosynthetic efficiency in Synechococcus. Utilizing label-free quantitative acetylome profiling, we identified 171 endogenous Kac sites across 137 proteins targeted by cKAT. These target proteins participate in diverse metabolic and photosynthetic pathways, indicating a broad regulatory role for cKAT in cellular physiology. Notably, ChpX, a key component of CO2-concentrating mechanisms, was prominently acetylated by cKAT both in vivo and in vitro. We further established that cKAT specifically mediates acetylation at residue K88 of ChpX, a modification that directly modulates CO2 uptake efficiency. This regulatory mechanism consequently influences photosynthetic performance and cellular growth in Synechococcus. Collectively, these findings establish cKAT as a central regulator of cyanobacterial carbon fixation. This work expands the known repertoire of photosynthetic acetyltransferases and provides mechanistic insights into the Kac-dependent regulation of photosynthetic processes.