Chinese Scientists Unravel cGNAT2 Role in Cyanobacteria

Cyanobacteria are a diverse group of gram-negative bacteria that perform plant-like oxygen photosynthesis and are believed to be the evolutionary ancestors of chloroplasts in higher plants. Lysine acetylation is an important regulatory posttranslational modification that controls photosynthesis and metabolic processes in cyanobacteria and plants.

Synechococcus PCC 7002 is a unicellular cyanobacterium that has been used as a model organism to study photosynthesis. 802 acetylated proteins have been identified in Synechococcus PCC 7002, but the enzymes that regulate reversible lysine acetylation in cyanobacteria remain largely unknown.

Recently, a research team led by Prof. GE Feng of the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences illustrated the structure, function and mechanism of lysine acetyltransferase in cyanobacteria, and identified acetylation in regulating the growth and photosynthesis of Synechococcus. PCC 7002. This study was published in Plant Physiology.

In this study, the researchers identified 16 predicted lysine acetyltransferases (KATs) in the Synechococcus PCC 7002 genome using bioinformatic analyses, and tested these KATs using an acetylation-deficient E. coli strain lacking all known acetylation mechanisms. They discovered the presence of the lysine acetyltransferase cyanobacterial Gcn5-related N-acetyltransferase (cGNAT2) in cyanobacteria, and that knocking out this gene significantly affected photosynthesis in cyanobacteria.

The researchers then used AlphaFold2 to predict the structure of cGNAT2 and found that it forms a homodimeric structure. This protein has the ability to bind both substrate proteins and acetyl-CoA, allowing it to exert catalytic activity. The binding region between cGNAT2 and acetyl-CoA was identified by molecular docking. Further confirmation was obtained by site-specific mutations and in vitro enzyme activity experiments, which demonstrated the critical role of eight specific amino acid residues in maintaining the activity of the enzyme.

Based on acetyllysine enrichment and label-free quantitative (LFQ) acetylome techniques, the researchers demonstrated that cGNAT2 can catalyze lysine acetylation in NAD(P)H dehydrogenase J (NdhJ) to regulate its enzymatic activity in vivo and in vitro, which may underlie changes in cell growth and photosynthetic electron transport.

This study presents the first report of the lysine acetyltransferase cGNAT2 in cyanobacteria, and elucidates its molecular mechanism in regulating substrate protein acetylation modifications in cyanobacteria. It will improve the understanding of the mechanisms underlying extensive lysine acetylation in cyanobacteria, as well as the mechanisms regulating photosynthesis in photosynthetic organisms.