The human genome project has allowed for the rapid identification of a large number of protein families based on similarities in their genetic sequences. In the present study, I report the functional characterization of a 44 kDa protein that functions in cardiolipin synthesis and remodeling. Although it is present in most tissues, it is abundant in multiple brain regions including olfactory bulbs, hippocampus, cerebellum, cortex, and brain stem, and is detectable in both primary neurons and glial cells. In assays performed in vitro, this protein significantly increased the incorporation of [14C]oleoyl-CoA into phosphatidylinositol and CL using either lysophosphatidylinositol, or monolysocardiolipin or dilysocardiolipin as acyl acceptors, respectively. This protein did not display significant acyltransferase activity with a number of other lysophospholipid acyl acceptors. Overexpressing this enzyme in HEK-293 cells increased total CL content, but did not significantly affect levels of other glycerophospholipids. Analysis of the fatty acyl profile of CL from cells overexpressing this protein indicated increased total saturated fatty acids, particularly stearate, palmitate, and myristate, and increased levels of n-3 polyunsaturated fatty acids α-linoleic acid (18:3n-3), eicosatrienoic acid (20:3n-3), and eicosapentanoic acid (20:5n-3). In accordance with its observed role in CL remodeling, subcellular localization of this protein was predominately mitochondrial. This protein is also regulated during embryogenesis, and in varying metabolic states.

The human genome project has allowed for the rapid identification of a large number of protein families based on similarities in their genetic sequences. The acyl-glycerol phosphate acyltransferase (AGPAT) family of enzymes have been largely identified through sequence homology, with eleven isoforms identified in both mice and humans. Interestingly, very little work has been done on the characterization of AGPAT isoform 4. In the present study, I report the functional characterization of AGPAT4 as an acyl-CoA: lysocardiolipin acyltransferase (ALCAT), which we have renamed ALCAT2. Although ALCAT2 is present in most tissues, it is abundant in multiple brain regions including olfactory bulbs, hippocampus, cerebellum, cortex, and brain stem, and is detectable in both primary neurons and glial cells. In assays performed in vitro, ALCAT2 significantly increased the incorporation of [14C]oleoyl-CoA into phosphatidylinositol and CL using either lysophosphatidylinositol, or monolysocardiolipin or dilysocardiolipin as acyl acceptors, respectively. ALCAT2 did not display significant acyltransferase activity with lysophosphatidic acid, lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylserine, or lysophosphatidylglycerol acyl acceptors. Overexpressing ALCAT2 in HEK-293 cells increased the total CL content, but did not significantly affect levels of other glycerophospholipids including phosphatidylinositol. Analysis of the fatty acyl profile of CL from ALCAT2-overexpressing cells indicated increased total saturated fatty acids, particularly stearate, palmitate, and myristate, and increased levels of n-3 polyunsaturated fatty acids α-linolenic acid (18:3n-3), eicosatrienoic acid (20:3n-3), and eicosapentanoic acid (20:5n-3). In accordance with its observed role in cardiolipin remodeling, ALCAT2 localized predominately to the mitochondria. ALCAT2 was also regulated during embryogenesis, and in varying metabolic states. In summary, ALCAT2 is a new enzyme in CL remodeling with a potential role in mitochondrial function.