Prenol Lipids

From LipidomicsWiki

Prenols (PR) are synthesized from the five carbon precursors isopentenyl diphosphate and dimethylallyl diphosphate that are produced mainly via the mevalonic acid pathway In some bacteria (e.g., Escherichia coli) and plants, isoprenoid precursors are made by the methylerythritol phosphate pathway. Because the simple isoprenoids(linear alcohols, diphosphates, etc.) are formed by the successive addition of C5 units, it is convenient to classify them in this manner, with a polyterpene subclass for those structures containing more than 40 carbons(i.e., 8 isoprenoid units).

Note that vitamin A and its derivatives and phytanic acid and its oxidation product pristanic acid are grouped under C20 isoprenoids. Carotenoids are important simple isoprenoids that function as antioxidants and as precursors of vitamin A. Another biologically important class of molecules is exemplified by the quinones and hydroquinones, which contain an isoprenoid tail attached to a quinonoid core of nonisoprenoid origin. Vitamins E and K as well as the ubiquinones are examples of this class.

PR and their phosphorylated derivatives play important roles in the transport of oligosaccharides across membranes. Polyprenol phosphate sugars and polyprenol diphosphate sugars function in extracytoplasmic glycosylation reactions, in extracellular polysaccharide biosynthesis [for instance, peptidoglycan polymerization in bacteria], and in eukaryotic protein N-glycosylation. The biosynthesis and function of polyprenol phosphate sugars differ significantly from those of the polyprenol diphosphate sugars. Bacteria synthesize polyprenols(called bactoprenols) in which the terminal isoprenoid unit attached to oxygen remains unsaturated, whereas in animal polyprenols (dolichols) the terminal isoprenoid is reduced. Bacterial polyprenols are typically 10 to 12 units long, whereas dolichols usually consist of 18 to 22 isoprene units. In the phytoprenols of plants, the three distal units are reduced.