Global Profiling of Lysine Succinylation Reveals Acetylation Crosstalk Underlying Metabolic Regulation in <i>Chlamydomonas reinhardtii</i>

Lysine succinylation is an evolutionarily conserved post-translational modification (PTM) involved in cellular metabolic regulation. <i>Chlamydomonas reinhardtii</i>, a GRAS-certified microalga and emerging chassis for biofuel and biobased production, has not yet been systematically characterized for succinylation. Here, we present a comprehensive proteome-wide lysine succinylome map of <i>Chlamydomonas</i> and identify 2806 high-confidence succinylation sites across 791 proteins. These proteins were predominantly distributed in chloroplasts, cytoplasm, and mitochondria and were significantly enriched in pathways central to carbon and lipid metabolism. Comparative analyses revealed extensive crosstalk between succinylation and acetylation with distinct sequence patterns and functional preferences. Site-directed mutagenesis and enzymatic assays revealed that succinylation at K597 of Acetyl-CoA synthetase 3 (ACS3) markedly reduced enzymatic activity, with an inhibitory effect stronger than that of acetylation. These findings establish succinylation as a key metabolic regulator and provide a valuable resource for advancing metabolic engineering in algae.