Lysophosphatidylcholine acyltransferase-1 (LPCAT1) plays a critical role in the remodeling of phosphatidylcholines (PCs) in cellular lipidome. However, evidence is scarce regarding its sn-selectivity, viz. the preference of assembling acyl-Coenzyme A (CoA) at the C1 or C2-hydroxyl on a glycerol backbone because of difficulty to quantify the thus-formed PC snisomers. We have established a multiplexed assay to measure both sn-and acyl-chain selectivity of LPCAT1 toward a mixture of acyl-CoAs by integrating isomerresolving tandem mass spectrometry. Our findings reveal that LPCAT1 shows exclusive sn-1 specificity regardless of the identity of acyl-CoAs. We further confirm that elevated PC 18 : 1/16:0 relative to its snisomer results from an increased expression of LPCAT1 in human hepatocellular carcinoma (HCC) tissue as compared to normal liver tissue. MS imaging via desorption electrospray ionization of PC 18 : 1/16:0 thus enables visualization of HCC margins in human liver tissue at a molecular level.Glycerophospholipids (GPLs) are essential components of all biological membranes. [1] This important category of lipids shares three common building blocks, a glycerol backbone, two fatty acyls linked to the C-1 and C-2 hydroxyls of the glycerol, and a phosphate-containing head group esterified at the C-3 hydroxyl. For individual GPL molecules, saturated and monounsaturated fatty acids tend to be esterified at the C-1 position or so-called sn-1 position of the glycerol, whereas polyunsaturated fatty acids, such as arachidonic acid, are commonly located at the C-2 position or sn-2 position. [2] Such an asymmetric distribution of acyl chains is regulated by the remodeling pathway (Land's cycle), [3] where phospholipase A 1 or A 2 (PLA 1 /PLA 2 ) converts GPLs to 2-acyl lysophospholipids or 1-acyl lysophospholipids (LPLs), while lysophospholipid acyltransferases (LPLATs) re-acylate LPLs back to GPLs. For instance, the expression patterns of lysophosphocholine acyltransferases (LPCATs) and their activities toward different acyl-CoAs in a specific tissue type contributes to the molecular diversity of phosphatidylcholines (PCs) in the tissue. [4] LPCAT1 is highly expressed in lung tissue and it catalyzes the production of dipalmitoyl-phosphatidylcholine (PC 16:0/ 16:0), a major lipid component of pulmonary surfactant. [5] A previous study suggests that LPCAT1 has a preference toward saturated fatty acyl-CoAs, e.g., C16:0 and C14:0. [5b] Recently, several groups reported that the compositions of PC sn-isomers were significantly different in cancer tissue relative to normal control, showing a great potential in disease phenotyping. [6] Knowing the sn-selectivity of LPCAT1 will thus provide valuable insights into the metabolic origins of the altered lipid compositions.Mass spectrometry (MS) has become the method of choice for developing new enzymatic assays, owing to its high sensitivity, structural specificity, and high-throughput analysis capability. [7] Assays based on liquid chromatography-mass spectrometry (LC-MS) have b...
Lysophosphatidylcholine acyltransferase‐1 (LPCAT1) plays a critical role in the remodeling of phosphatidylcholines (PCs) in cellular lipidome. However, evidence is scarce regarding its sn‐selectivity, viz. the preference of assembling acyl‐Coenzyme A (CoA) at the C1 or C2‐hydroxyl on a glycerol backbone because of difficulty to quantify the thus‐formed PC sn‐isomers. We have established a multiplexed assay to measure both sn‐ and acyl‐chain selectivity of LPCAT1 toward a mixture of acyl‐CoAs by integrating isomer‐resolving tandem mass spectrometry. Our findings reveal that LPCAT1 shows exclusive sn‐1 specificity regardless of the identity of acyl‐CoAs. We further confirm that elevated PC 18 : 1/16:0 relative to its sn‐isomer results from an increased expression of LPCAT1 in human hepatocellular carcinoma (HCC) tissue as compared to normal liver tissue. MS imaging via desorption electrospray ionization of PC 18 : 1/16:0 thus enables visualization of HCC margins in human liver tissue at a molecular level.
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