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In biochemistry, an ether lipid refers to any lipid in which the lipid "tail" group is attached to the glycerol backbone via an ether at any position. In contrast, conventional glycerophospholipids and triglycerides are tri. Structural types include:
Based on whether the sn-1 lipid is unsaturated next to the ether linkage, they can be further divided into alkenyl-acylphospholipids ("plasmenylphospholipid", 1-0-alk-1’-enyl-2-acyl-sn-glycerol) and alkyl-acylphospholipids ("plasmanylphospholipid"). This class of lipids have important roles in human cell signaling and structure.
The term "plasmalogen" can refer to any ether lipid with a Enol ether linkage, i.e. ones with a carbon-carbon double bond next to the ether linkage. Without specification it generally refers to alkenyl-acylphospholipids, but "neutral plasmalogens" (alkenyldiacylglycerols) and "diplasmalogens" (dialkenylphospholipids) also exist.
The conversion of an ordinary saturated ether lipid into a plaminogen is achieved by plasmanylethanolamine desaturase (PEDS1), which catalyzes an aerobic oxidation in the endoplamic reticulum.
Monoalkylglycerol ethers (MAGEs) are also generated from 2-acetyl MAGEs (precursors of platelet-activating factor) by KIAA1363.
1-alkyldiacyl- sn-glycerols, i.e. the ether analog of triglycerides, also occur in animals. They are present in very small amounts in mammals. They are found in very high amounts in the livers of marine animals, both vertebrates like sharks (especially spiny dogfish and ratfish) and invertebrates like squids. They are also found in all corals.
A toxic ether lipid analogue miltefosine has recently been introduced as an oral treatment for the tropical disease leishmaniasis, which is caused by leishmania, a protozoal parasite with a particularly high ether lipid content in its membranes.
Among different groups of archaea, diverse modifications on the basic archaeol backbone have emerged.
Some groups of bacteria have, like archaea, evolved tetraether lipids (so-called brGDGT). These differ from archaeal ones by their chirality and the non-isoprenoid structure.
In eukaryotes
Biosynthesis
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.
Functions
Structural
Plasmalogens as well as some 1-O-alkyl lipids are ubiquitous and sometimes major parts of the in . The glycosylphosphatidylinositol anchor of mammalian proteins generally consist of an 1-O-alkyl lipid.
Second messenger
Differences between the catabolism of ether glycerophospholipids by specific might be involved in the generation of lipid second messenger systems such as and arachidonic acid that are important in signal transduction. Ether lipids can also act directly in cell signaling, as the platelet-activating factor is an ether lipid signaling molecule that is involved in leukocyte function in the mammalian immune system.
Antioxidant
Another possible function of the plasmalogen ether lipids is as , as protective effects against oxidative stress have been demonstrated in cell culture and these lipids might therefore play a role in serum lipoprotein metabolism. This antioxidant activity comes from the enol ether double bond being targeted by a variety of reactive oxygen species.
Synthetic ether lipid analogs
Synthetic ether lipid analogs have chemotherapy properties, probably by disrupting membrane structure and acting as enzyme inhibitor of enzymes within signal transmission pathways, such as protein kinase C and phospholipase C.
In archaea
The cell membrane of archaea consist mostly of ether phospholipids. These lipids have a flipped chirality compared to bacterial and eukaryotic membranes, a conundrum known as the "lipid divide". The "tail" groups are also not simply n-alkyl groups, but highly methylated chains made up of saturated isoprenoid units (e.g. phytanyl).
In bacteria
Ether phospholipids are major parts of the cell membrane in anaerobic bacteria. These lipids can be variously 1-O-alkyl, 2-O-alkyl, or 1,2-O-dialkyl. Plasminogens also exist, but they are made by anaerobic reduction from an ester as opposed to the aerobic eukaryotic process.
See also
External links
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