Abstract
Chain-length-specific subsets of diacylglycerol (DAG) lipids are proposed to regulate differential physiological responses ranging from signal transduction to modulation of the membrane properties. However, the mechanism or molecular players regulating the subsets of DAG species remain unknown. Here, we uncover the role of a conserved eukaryotic protein family, DISCO-interacting protein 2 (DIP2) as a homeostatic regulator of a chemically distinct subset of DAGs using yeast, fly, and mouse models. Genetic and chemical screens along with lipidomics analysis in yeast reveal that DIP2 prevents the toxic accumulation of specific DAGs in the logarithmic growth phase, which otherwise leads to endoplasmic reticulum stress. We also show that the fatty acyl-AMP ligase-like domains of DIP2 are essential for the redirection of the flux of DAG subspecies to storage lipid, triacylglycerols. DIP2 is associated with vacuoles through mitochondria–vacuole contact sites and such modulation of selective DAG abundance by DIP2 is found to be crucial for optimal vacuole membrane fusion and consequently osmoadaptation in yeast. Thus, the study illuminates an unprecedented DAG metabolism route and provides new insights on how cell fine-tunes DAG subspecies for cellular homeostasis and environmental adaptation.
Lipids, such as fats and hormones, constitute one of the main building blocks of cells. There are thousands of different lipids each with distinctive chemical properties that allow them to carry out specific roles. For example, a group of lipids called diacylglycerols help cells perform a myriad of tasks, like sensing external signals, making membranes, and storing energy. The production and breakdown of diacylglycerols is therefore tightly regulated. However, very little is known about the molecules involved in this metabolic process.
One possible candidate is the enzyme DIP2 which is comprised of a protein module known as FAAL (short for fatty acyl-AMP ligase). FAAL belongs to a family of enzymes that synthesize lipid-like molecules in bacteria. In 2021, a group of researchers tracked the evolutionary trajectory of these bacterial proteins and found that most of them were lost in eukaryotes, such as animals and fungi. FAAL-like proteins, however, had been retained through evolution and incorporated in to DIP2.
Here, Mondal, Kinatukara et al. – including some of the researchers involved in the 2021 study – have used a combination of genetic and biochemical experiments to investigate whether and how DIP2 contributes to lipid metabolism in eukaryotes. They found that yeast cells without the gene for DIP2 had higher levels of diacylglycerols which hampered the shape and function of certain cellular compartments. The mutant cells were also unable to convert diacylglycerols in to another group of lipids which are involved in energy storage. This effect was observed in fruit flies and mice lacking DIP2, suggesting that this role for DIP2 is conserved across most eukaryotes.
Further experiments in yeast cells revealed that unlike other enzymes that metabolize diacylglycerols, DIP2 only acted on a sub-population of diacylglycerols at specific locations and times. Furthermore, yeast cells lacking DIP2 could still grow under ideal conditions, but could not cope with high or low salt concentrations in their surroundings, suggesting that the enzyme helps cells deal with environmental stresses.
Since DIP2 is found in most eukaryotes, understanding how it works could be useful for multiple branches of biology. For example, some pathogenic fungi that cause diseases in crop plants and humans also rely on DIP2. Further studies are needed to better understand the role that DIP2 plays in other eukaryotic species which may shed light on other processes the enzyme is involved in.
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