Lipids are essential for cellular functions and signaling processes. Yet they are understudied compared to other biological molecules such as proteins mainly due to a lack of appropriate methodology. Compared to proteins, it is very difficult to introduce perturbations such as concentration changes and it is further very challenging to visualize lipids especially in a cellular context. This has mainly to do with both the size and also the chemical diversity of lipids. Chemical biology approaches such as the introduction of photolabile moieties, photocrosslinking- and click chemistry-groups offer the possibility to fill this methodological gap and in particular to address biological questions on the level of individual lipid species. Using phosphatidic acid as an exemplary lipid class, we will employ such an approach to understand how individual lipid species can exert a specific function in the cell and how minor structural differences can influence lipid dynamics in the membranes and interactions with proteins.
Phosphatidic acid (PA) constitutes a class of glycerophospholipids that not only plays a central role in phospholipid synthesis but also in cell signaling. PAs are involved in regulating and amplifying multiple cellular and physiological processes in mammalian cells, such as the MAPK, HIPPO and mTOR pathway. Furthermore, PA is involved in the regulation of processes involving membrane remodeling, such as endo- and exocytosis and cell migration. The synthesis of PA is versatile since it is produced by different synthetic routes located at distinct subcellular structures, for example at the plasma membrane, mitochondria or the endoplasmic reticulum. Variations in the fatty acid composition of PA depend on which precursor species predominates at the respective organelle, such as phosphatidyl choline, lysophosphatidic acid or diacylglycerol. As for many signaling lipids involved in the regulation of multiple signaling pathways, the key question is how signal specificity is achieved. Therefore, it is crucial to be able to precisely modulate the levels of distinct molecular PA species at different subcellular structures. Whereas methodology for more prominent signaling lipids, such as diacylglycerols, sphingosine and phosphatidylinositol phosphates, are already available, tools and assays to dissect species and organelle specificity in PA signaling are scarce. In the Schuhmacher Lab we aim at closing this methodological gap and investigating the organelle- and location-specificity of PA signaling.