Triacylglycerol synthesis for lipid droplet formation

Lipid droplets form in the endoplasmic reticulum membrane when neutral lipids, chiefly triacylglycerol and sterol esters, are made between the two leaflets, coalesce into a lens and bud toward the cytosol as an oil core covered by a phospholipid monolayer. The committed step of triacylglycerol storage is the acylation of diacylglycerol, catalysed in eukaryotes by two unrelated acyl-CoA-dependent enzyme families, DGAT1 and DGAT2, either of which can supply a droplet. This module is the eukaryote-wide core of that step, written so that it can be evaluated in any genome.

Eukaryote-wide scope: PAINT places the DGAT1 and DGAT2 nodes cited here at Eukaryota (taxon:2759) with F:GO:0004144; each node is shown to be an ancestor of the human protein by its IBA rows or its IBD seeds. Read as a satisfiability rule, a genome needs at least one of the two DGAT families (a ONE_OR_MORE realizer set). FIT proteins are optional (see that part). Molecular functions come from the human DGAT1 and DGAT2 reviews, and for FIT from the node's F IBD. Selector caveats are on each family: both DGAT variants use the subfamilies their family reviews allow and may miss other lineages', and no yeast DGAT1 is listed. Not modelled: seipin, which organizes droplet nucleation sites but whose human protein (BSCL2) has no local PANTHER entry; the acyl-CoA-independent PDAT route (yeast Lro1, fission yeast Plh1, plant PDAT1), which has no human member; and the perilipins and other surface proteins, which are lineage-specific. The sterol acyltransferases (Are1/Are2, SOAT1/SOAT2) make the sterol-ester half of the droplet core; they share PTHR10408 with DGAT1 and are excluded from it here, so the rule tests only triacylglycerol synthesis. The upstream glycerolipid pathway is described in triacylglycerol_biosynthesis.