Lysine Malonylation as a New Inflammatory Signal

Malonylation is a recently uncovered protein post-translational modification. It involves the attachment of a malonyl group to lysines, resulting in an extra 86 Da mass, as well as a change in charge comparable to that of phosphorylation. The enzyme responsible for malonylation has not yet been uncovered, but it seems like malonylation levels are dependent on malonyl-CoA concentration. The discovery of this new modification took place during a time in which immunometabolism became an emerging field and many studies into the metabolism of immune cells have recently highlighted the tight link existing between the metabolic status and the function of these cells. This led us to investigate whether protein malonylation might be a new mechanism by which the cell's metabolism can control the inflammatory response. We have been able to show that protein malonylation can be induced in macrophages following activation with various toll-like receptor ligands. In addition, the TLR4 ligand, LPS, can specifically increase malonylation of the glycolytic enzyme GAPDH in macrophages. Through mass-spec analysis we identified a single malonylated lysine present in GAPDH in resting macrophages, while two were identified following activation with LPS. Interestingly, GAPDH enzymatic activity increases under the same conditions. Furthermore, as part of the GAIT complex, GAPDH is capable of binding to the 3'-UTR region of the death-associated protein kinase (DAPK) mRNA and inhibit its translation. Our data would suggest that following activation, GAPDH releases DAPK mRNA. Overall, our results suggest that protein malonylation is an important signal for LPS signaling in macrophages, that may be responsible for controlling the functions of the glycolytic enzyme GAPDH following macrophage activation. This research is supported by Science Foundation Ireland.