PLAAT1 Exhibits Phosphatidylcholine:Monolysocardiolipin Transacylase Activity

Abstract

Tissue-specific cardiolipin fatty acyl profiles are achieved by remodeling of de novo synthesized cardiolipin, and four remodeling enzymes have thus far been identified. We studied the enzyme phospholipase A and acyltransferase 1 (PLAAT1), and we report the discovery that it has phosphatidylcholine (PC):monolysocardiolipin (MLCL) transacylase activity. Subcellular localization was analyzed by differential centrifugation and immunoblotting. Total levels of major phospholipids, and the fatty acyl profile of cardiolipin, were analyzed in HEK293 cells expressing murine PLAAT1 using gas chromatography. Apparent enzyme kinetics of affinity-purified PLAAT1 were calculated using radiochemical enzyme assays. This enzyme was found to localize predominantly to the endoplasmic reticulum (ER) but was detected at low levels in the mitochondria-associated ER matrix. Cells expressing PLAAT1 had higher levels of total cardiolipin, but not other phospholipids, and it was primarily enriched in the saturated fatty acids myristate, palmitate, and stearate, with quantitatively smaller increases in the n-3 polyunsaturated fatty acids linolenate, eicosatrienoate, and eicosapentanoate and the monounsaturated fatty acid erucate. Affinity-purified PLAAT1 did not catalyze the transacylation of MLCL using 1-palmitoyl-2-[14C]-linoleoyl-PC as an acyl donor. However, PLAAT1 had an apparent Vmax of 1.61 μmol/min/mg protein and Km of 126 μM using [9,10-3H]-distearoyl-PC as an acyl donor, and 0.61 μmol/min/mg protein and Km of 16 μM using [9,10-3H]-dioleoyl-PC. PLAAT1 is therefore a novel PC:MLCL transacylase.

Gene loss and relaxed selection of plaat1 in vertebrates adapted to low-light environments

“…While signal for relaxed selection and gene degradation across convergent lineages of LVAB species suggests that plaat1 retains some functional importance in eye development in mammals, it is also possible that plaat1 is associated with pleiotropic physiologies that are also altered in dark environments. For example, plaat1 is known to be involved in insulin signaling pathways, cardiolipin metabolism, as well as tumor suppression, which are also known to be important in shifts to darkness [22,38,39]. Additionally , plaat1 plays a role in p53-mediated apoptosis involved in starvation and disease, both of which are greatly modified in low-light environments [23].…”

“…While we focus here on the newly discovered lens clarification function that is apparent for plaat1 , it is important to note that plaat1 has several pleiotropic physiological interactions, which we do not fully understand [20–22,36,39,52]. Plaat family proteins are important for tumor suppression, NAPE biosynthesis (hormones released by the small intestine into the bloodstream to process fat), obesity, and peroxisome formation [20–22,36,39,52,53]. Particularly noteworthy is plaat1 ’s role in facilitating viral translocation, making viral coevolution another strong potential driver of convergent gene loss and/or degradation in vertebrates [53].…”

“…The copyright holder for this preprint this version posted December 13, 2023. ; https://doi.org/10.1101/2023.12.12.571336 doi: bioRxiv preprint Submission Proceeding of the Royal Society B-10 10 While we focus here on the newly discovered lens clarification function that is apparent for plaat1, it is important to note that plaat1 has several pleiotropic physiological interactions, which we do not fully understand [20][21][22]36,39,52]. Plaat family proteins are important for tumor suppression, NAPE biosynthesis (hormones released by the small intestine into the bloodstream to process fat), obesity, and peroxisome formation [20][21][22]36,39,52,53]. Particularly noteworthy is plaat1's role in facilitating viral translocation, making viral coevolution another strong potential driver of convergent gene loss and/or degradation in vertebrates [53].…”

“…Plaat family genes, which are phospholipases involved in N-acylethanolamine (NAE) biosynthesis, play a crucial role in lens clarification, as well as tumor suppression, satiation signaling, and viral translocation [20,21]. Recently, Plaat1 was found to play a critical role in the metabolism of lens organelles in zebrafish (affecting eye clarity), as well as cardiolipin synthesis and remodeling, which may be a key novel pathway for diabetes [22]. Specifically, the protein PLAAT1 is recruited to damaged organelle membranes in the lens during development, causing the rupture and clearance of lens organelles which is required for the development of a clear lens [21].…”

Phenotypic Characterization of Female Carrier Mice Heterozygous for Tafazzin Deletion

“…However, the enzymes involved in de novo synthesis pathways lack the acyl-chain specificity needed to create the signature molecular profiles that are evident in various tissues [ 2 ]. To this end, at least five cardiolipin remodeling enzymes have been identified [ 7 , 8 , 9 , 10 , 11 , 12 ]. These enzymes function to re-esterify fatty acyl chains onto monolyso- or dilyso-cardiolipin produced from the action of various phospholipases on nascent cardiolipin, resulting in the generation of a mature form of this complex lipid [ 2 ].…”