Recombinant PNPLA1 catalyzes the synthesis of acylceramides and acyl acids with selective incorporation of linoleic acid

Abstract

Loss-of-function mutations in patatin-like phospholipase domain-containing protein 1 (PNPLA1) cause autosomal recessive congenital ichthyosis, and altered PNPLA1 activity is implicated in the pathogenesis of atopic dermatitis and other common skin diseases. To examine the hypothesis that PNPLA1 catalyzes the synthesis of acylceramides and acyl acids, we expressed and partially purified a soluble, truncated form of PNPLA1 in Escherichia coli, (PNPLA1_trun) along with the related protein PNPLA2 (ATGL, adipose triglyceride lipase) and coactivator CGI-58. Liposomal substrates were incubated with recombinant enzymes for 0.5-24 h and products analyzed by HPLC-UV and LC-MS. Using trilinolein or dilinolein substrates, PNPLA1_trun, like ATGL_trun, catalyzed lipolysis and acyltransferase reactions with 2-30% conversion into linoleic acid, monolinolein, and trilinolein. CGI-58 enhanced ATGL-catalyzed lipolysis as previously reported, but transacylase activity was not enhanced with ATGL or PNPLA1. In matching the proposed activity in vivo, PNPLA1 catalyzed acyl transfer from trilinolein and dilinolein donors to omega-hydroxy ceramide, omega-hydroxy glucosylceramide, and omega-hydroxy acid acceptors to form acylceramide, glucosyl-acylceramide, and acyl acid, respectively, albeit with only ∼0.05% conversion of the substrates. Notably, in experiments comparing dilinolein vs. diolein acyl donors, PNPLA1 transferred linoleate with 3:1 selectivity over oleate into acylceramide. These results support the role for PNPLA1 in the synthesis of acylceramides and acyl acids in epidermis and suggest that the enrichment of these lipids with linoleic acid could result from the substrate selectivity of PNPLA1.

Keywords: Enzymology; LC/MS; acyltransferase; ceramide; epidermis; fatty acid metabolism; lipolysis; skin; skin barrier; triacylglycerol.