Abstract 2023 Function and Molecular Mechanism of the NatB-Mediated N-Terminal Acetylation in Lipid Metabolism

N-terminal acetylation, a prevalent protein modification catalyzed by N-terminal acetyltransferases, plays a crucial role in various cellular processes within eukaryotic cells. While many enzymes involved in lipid metabolism carry N-terminal acetyl groups, the precise physiological implications of these modifications remain elusive. In this study, we unveiled the significant impacts of the yeast N-terminal acetyltransferase B (NatB) on lipid metabolism. Cells with impaired NatB activity exhibited substantial accumulations of lipid droplets and triacylglycerol. Notably, Pah1 phosphatidate phosphatase, a key enzyme in triacylglycerol synthesis, emerged as a bona fide substrate of NatB. The catalytically inactive NatB acetyltransferase mutation (4A Nat3) exerted a stabilizing effect on the Pah1 protein, resulting in a remarkable 2.2-fold increase in protein content during the stationary phase. This stabilization, in turn, led to a concurrent 1.8-fold increase in triacylglycerol content and the accumulation of lipid droplets. Moreover, the introduction of a point mutation in Pah1 (Q2P Pah1), replacing the second glutamine residue with a proline residue known for abolishing N-terminal acetylation, resulted in elevated protein levels of Pah1. However, the disrupted essential N-terminal amphipathic helix in Pah1 due to the mutation led to decreased levels of triacylglycerol and lipid droplets.