Lipids construct cellular membranes and organelles and some of them serve as signaling molecules vital for regulation of cell functioning. Lipids are also a source of energy but their excessive accumulation in the body leads to obesity. Obesity is a significant issue worldwide and its prevention using traditional methods like exercise and diet may not always be effective. Fortunately, science can provide helpful solutions basing on the details of fat metabolism. Lipid metabolism involves the synthesis and breaking down of lipids assisted by numerous enzymes which thereby regulate the whole process. By understanding how those enzymes operate, new approaches to treating obesity and other diseases related to faulty metabolism of lipids could be developed.
A team led by Professor Katarzyna Kwiatkowska from the Nencki Institute of Experimental Biology in Warsaw conducted groundbreaking research that sheds light on a previously unknown mechanism that modulates the performance of an enzyme involved in lipid metabolism. The team comprised Gabriela Traczyk, Aneta Hromada-Judycka, Anna Świątkowska, Anna Ciesielska, and Julia Wiśniewska, each of which played a major role in this discovery. Their findings, published in the Journal of Lipid Research, represent a significant advancement in understanding cell signaling and lipid metabolism.
The scientists used intricate techniques to pinpoint a specific modification of the diacylglycerol kinase-ε (DGKε) molecule, S-palmitoylation, which consists in adding a fatty acid (palmitic acid, a common component of dietary fats) residue to the enzyme. These rigorous methods included cloning of DGKε variants with single amino acid residues changed relative to the native form, transfecting DGKε into cultured human kidney cells, and utilizing specialized chemical techniques like click-based chemistry. These techniques highlighted the precision and thoroughness of the research, leading to solid and dependable results.
Professor Kwiatkowska explains “In our research, we first discovered the specific cysteine that undergoes S-palmitoylation in DGKε. This amino acid is located at the cytoplasmic side of DGKε integrated into the membrane of organelles. We then used two complementary labeling (acyl-polyethylene glycol and acyl-biotin exchange) techniques to reveal enzymes (called zDHHC) performing the S-palmitoylation. We found solid proof of the DGKε S-palmitoylation that is likely to affect the conversion of diacylglycerol into phosphatidic acid, a pivotal step in the synthesis of certain lipids.
The scientists also used micelles with diacylglycerol to examine the activity of the investigated enzyme, revealing a decrease in DGKε activity after S-palmitoylation. Micelles are small spherical structures formed by molecules, such as diacylglycerol, with a hydrophobic and a hydrophilic region in water solutions. The researchers also examined the cellular localization of DGKε and, in addition to the expected detection of DGKε in the endoplasmic reticulum where most of the lipids are synthesized, they also found the kinase in the Golgi apparatus. They speculated on the possibility of the impact of S-palmitoylation of DGKε on its cellular transport and localization.
M.Sc. Traczyk explains “Our findings suggest the presence of a small pool of DGKε within the Golgi apparatus, leading us to propose its involvement in the specific aspect of lipid synthesis. While further studies of native DGKε can reveal the exact role of DGKε in the Golgi apparatus, our research opens new avenues in studies on the involvement of this enzyme in the phosphoinositol signaling cycle and general lipid metabolism.”
This pioneering research, conducted by Professor Kwiatkowska’s team, suggests that S-palmitoylation could fine-tune DGKε activity within specific cellular compartments. This would significantly advance our understanding of cell signaling and lipid metabolism and can pave the way for novel therapeutic strategies in obesity and other diseases.
Journal Reference
Gabriela Traczyk, Aneta Hromada-Judycka, Anna Świątkowska, Julia Wiśniewska, Anna Ciesielska, Katarzyna Kwiatkowska. “Diacylglycerol kinase-ε is S-palmitoylated on cysteine in the cytoplasmic end of its N-terminal transmembrane fragment.” Journal of lipid research 65(1) (2023) 100480. DOI: https://doi.org/10.1016/j.jlr.2023.100480
About the Authors
Gabriela Traczyk is a PhD cstudent, she works in the Laboratory of Molecular Membrane Biology of the Nencki Institute of Experimental Biology in Warsaw. Her studies focus on the functioning of DGKε kinase. Mutations in the gene encoding DGKε lead to a kidney disease called atypical hemolytic uremic syndrome (aHUS), and studies of Ms. Traczyk aim to elucidate the impact of these mutations on the stability and enzymatic activity of DGKε. She is also the leading co-author of the study revealing S-palmitoylation of DGKε (ORCID: https://orcid.org/0000-0003-2065-440X).
Aneta Hromada-Judycka, a postdoctoral researcher at the Laboratory of Molecular Membrane Biology of the Nencki Institute of Experimental Biology in Warsaw. She obtained her PhD in 2011 and joined the Laboratory in 2013. Her studies focus on elucidating molecular mechanisms of TLR4 signaling. TLR4 is a plasma membrane receptor activated by bacterial lipopolysaccharide (LPS) during infection, and uncontrolled TLR4 activity can lead to sepsis. Dr. Hromada-Judycka has conducted studies on the role of lipids, particularly phosphatidylinositol derivatives, in TLR4 receptor signaling cascades. She is a co-author of a proteomic study on protein palmitoylation in LPS-stimulated macrophages stimulated, which revealed that DGKε kinase, one of the enzymes controlling the level of phosphatidylinositol, is modified by S-palmitoylation. The work presented here of which Dr. Hromada-Judycka is a leading co-author, is a consequence of that discovery (ORCID: https://orcid.org/0000-0002-4449-882X).
