Fat droplet coating
Perilipin — The Droplet Coat
Also searched as Perilipin — The Droplet Coat.
The balance here is state, not amount. In the fed state this coat is doing its job: it covers the fat and sequesters the activator, keeping breakdown low — and that is correct, not a fault. Losing it entirely is not the goal; people with mutations in it have unrestrained fat release and severe insulin resistance. What you want is a lid that opens on demand. When the kinase phosphorylates it, three serines at one end dock the second lipase and two at the other release the first lipase's activator — one protein, two jobs, both essential.
In depth
The coat protein sitting over stored fat, holding the main lipase's activator hostage until it is told to let go.
What drives it
Lipolysis signal increases it.
The unlock, resolved to individual serines. 'The phosphorylation of three N-terminal serine residues of perilipin 1A facilitates the docking of PKA-phosphorylated hormone-sensitive lipase through a protein-protein interaction with the perilipin scaffold... The PKA-mediated phosphorylation of two carboxyl-terminal serine residues of perilipin 1A facilitates the release of CGI-58 from perilipin 1A, enabling interaction of CGI-58 with ATGL, in turn, activating the lipase' (PMC4274058). One protein, two jobs, different ends. PMC4274058
The Coat Eraser reduces it.
'PP1 also constitutes the predominant perilipin phosphatase in adipocytes' (doi 10.3389/fphys.2022.826314). The source does not overclaim: 'definitive proof remains elusive and likely requires a cell model lacking PP1 activity. In fact, PP1, PP2A and PP2C all have a significant activity against HSL.'. doi 10.3389/fphys.2022.826314
Fat-tissue signal (TNF-α) reduces it.
The mechanism is demolition, not unlocking. 'The ability of TNF-alpha to phosphorylate extracellular signal-regulated kinase 1 (ERK1) and ERK2 and to downregulate perilipin (which has been implicated in the lipolytic effect of TNF-alpha)' (PMID 14693700). ⇒ It tears down the droplet coat rather than phosphorylating it open — which is why the release is uncontrolled rather than on-demand. PMID 14693700
Nitric oxide kinase increases it.
The second road reaches the same two targets as the first — including the droplet coat. 'Les peptides natriurétiques stimulent l'activité guanylyl cyclase (GC) du récepteur NPR-A... induisent une augmentation des taux de GMPc, l'activation d'une PROTÉINE kinase G (PKG, cGK-I) puis LA phosphorylation ET L'activation DE LA PÉRILIPINE ET DE LA LHS' (Sengenes, Moro, Galitzky, Berlan, Lafontan — médecine/sciences 2005;21:61-5 — FRANÇAIS). And its power is quantified against the reference stimulant: 'Les peptides natriurétiques exercent UN PUISSANT EFFET LIPOLYTIQUE, leur effet maximal est SIMILAIRE À CELUI DE L'ISOPRÉNALINE.' Proven in living people by microdialysis: 'L'administration d'un β-bloquant NE supprime QUE TRÈS partiellement la mobilization lipidique induite par l'exercice physique alors qu'elle supprime totalement les effets d'un agoniste β-adrénergique... LA mobilization lipidique RÉSISTANT AU β-BLOQUANT EST due AUX peptides NATRIURÉTIQUES.' Blocking the epinephrine road barely dents fat mobilization during exercise, because a second road is carrying it — and under an oral beta-blocker mobilization was paradoxically improved.
What it drives
It reduces Fat-releasing enzyme (ATGL).
The hostage mechanism, and it is why ATGL has almost NO direct inputs. 'Under basal (fed) conditions, perilipin 1A provides a protective barrier against lipolysis of stored triacylglycerols and binds CGI-58, a coactivator of ATGL. When CGI-58 is sequestered on the perilipin scaffold, it cannot interact with OR activate ATGL' (PMC4274058). doi 10.3389/fphys.2022.826314 adds that ATGL is further held shut by direct binders: 'Other accessory proteins can further inhibit ATGL activity through their direct protein-protein interaction with ATGL, including G0/S2 switch protein 2 (G0S2), hypoxia-induced lipid droplet-associated protein (HILPDA), and fat specific protein 27 (FSP27).'. doi 10.3389/fphys.2022.826314 · PMC4274058
It reduces Lipase activator.
The hostage-taking, stated plainly. 'The ATGL-activating function of CGI58 is repressed by its binding to PLIN1, a lipid droplet scaffold, under basal conditions' (doi 10.3389/fphys.2022.826314). And from the mechanism paper: 'When CGI-58 is sequestered on the perilipin scaffold, it cannot interact with OR activate ATGL' (PMC4274058). ⇒ how much activator you have is irrelevant if none of it is released. doi 10.3389/fphys.2022.826314 · PMC4274058
It reduces Lipase switch-on.
The coat is not the door — it is permission to work once inside. This was settled by removing every mark site from the coat protein and watching what still happened: 'PKA-induced HSL translocation was independent of perilipin phosphorylation. However, [the mutant] failed to enhance PKA-stimulated lipolysis... Thus, the lipolytic action(S) of HSL at the LD surface requires PKA-dependent perilipin phosphorylation' (PMID 16595669 — Perilipin promotes hormone-sensitive lipase-mediated adipocyte lipolysis via phosphorylation-dependent and -independent mechanisms). ⇒ the lipase still arrives without the coat being marked. It simply cannot do anything when it gets there. That is a sharper and more useful statement than the usual one about the coat 'blocking access'. PMID 16595669
Blends that modulate it
Each blend page names this pathway and carries the study behind its claim.
See it on the map
Open the causal map to follow this pathway upstream and downstream, arrow by arrow, each with its study.