Ether lipid

In an organic chemistry general sense, an ether lipid implies an ether bridge between an alkyl group (a lipid) and an unspecified alkyl or aryl group, not necessarily glycerol. If glycerol is involved, the compound is called a glyceryl ether, which may take the form of an alkylglycerol, an alkyl acyl glycerol, or in combination with a phosphatide group, a phospholipid. In a biochemical sense, an ether lipid usually implies glycerophospholipids of various type, also called phospholipids, in which the sn-1 position of the glycerol backbone has a lipid attached by an ether bond and a lipid attached to the sn-2 position via an acyl group. This is in contrast to the more common glycerophospholipids, 1,2-diacyl-sn-glycerol (DAG), in which the glycerol backbone sn-1 and sn-2 positions have acyl chains attached by ester bonds. Ether lipid may also refer to alkylglycerols, such as chimyl (16:0), batyl (18:0), and selachyl (18:1 n-9) alcohols, with an ether-bound lipid on position sn-1, and the other two positions on the glycerol backbone unoccupied. There are two types of ether lipids, plasmanyl- and plasmenyl-phospholipids. Plasmanyl-phospholipids have an ether bond in position sn-1 to an alkyl group. Plasmenyl-phospholipids have an ether bond in position sn-1 to an alkenyl group, 1-0-alk-1’-enyl-2-acyl-sn-glycerol (AAG). The latter type is called plasmalogens. Platelet-activating factor (PAF) is an ether lipid which has an acetyl group instead of an acyl chain at the second position (SN-2). The formation of the ether bond in mammals requires two enzymes, dihydroxyacetonephosphate acyltransferase (DHAPAT) and alkyldihydroxyacetonephosphate synthase (ADAPS), that reside in the peroxisome. Accordingly, peroxisomal defects often lead to impairment of ether-lipid production. Monoalkylglycerol ethers (MAGEs) are also generated from 2-acetyl MAGEs (precursors of PAF) by KIAA1363. Plasmalogens as well as some 1-O-alkyl lipids are ubiquitous and sometimes major parts of the cell membranes in mammals and anaerobic bacteria.