Guide Lipids: Structure and Function. A Comprehensive Treatise

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Figures and Tables. Citations Publications citing this paper. What was ground? References Publications referenced by this paper. Fatty acid metabolism and its regulation Friedrich Spener. Lipid Analysis, 2nd edn. The biochemistry of plants. A comprehensive treatise. Volume 4.

Lipids: structure and function. Paul K. Geometrical and positional fatty acid isomers Edward A. Some aquatic organisms contain sphingolipids in which the phosphate is replaced by a phosphono or arsenate group. Some examples of sphingolipid structures are shown in Fig. The sterol category is subdivided primarily on the basis of biological function. The sterols, of which cholesterol and its derivatives are the most widely studied in mammalian systems, constitute an important component of membrane lipids, along with the glycerophospholipids and sphingomyelins There are many examples of unique sterols from plant, fungal, and marine sources that are designated as distinct subclasses in this schema Table 8.

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The steroids, which also contain the same fused four ring core structure, have different biological roles as hormones and signaling molecules These are subdivided on the basis of the number of carbons in the core skeleton. The C 18 steroids include the estrogen family, whereas the C 19 steroids comprise the androgens such as testosterone and androsterone.

The C 21 subclass, containing a two carbon side chain at the C 17 position, includes the progestogens as well as the glucocorticoids and mineralocorticoids. Additional classes within the sterols category are the bile acids 33 , which in mammals are primarily derivatives of cholanoic acid synthesized from cholesterol in the liver and their conjugates sulfuric acid, taurine, glycine, glucuronic acid, and others. Sterol lipid structures are shown in Fig.

Prenols 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. Because the simple isoprenoids linear alcohols, diphosphates, etc. Note that vitamin A and its derivatives and phytanic acid and its oxidation product pristanic acid are grouped under C 20 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 38 , 39 as well as the ubiquinones 40 are examples of this class. Polyprenols 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 41 , in extracellular polysaccharide biosynthesis [for instance, peptidoglycan polymerization in bacteria 42 ], and in eukaryotic protein N -glycosylation 43 , The biosynthesis and function of polyprenol phosphate sugars differ significantly from those of the polyprenol diphosphate sugars; therefore, we have placed them in separate subclasses.

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 40 , whereas dolichols usually consist of 18 to 22 isoprene units. In the phytoprenols of plants, the three distal units are reduced. Several examples of prenol lipid structures are shown in Fig. In fact, all eight lipid categories in the present scheme include important glycan derivatives, making the term glycolipid incompatible with the overall goal of lipid categorization.

In the saccharolipids Table 10 , a sugar substitutes for the glycerol backbone that is present in glycerolipids and glycerophospholipids. Saccharolipids can occur as glycan or as phosphorylated derivatives. The most familiar saccharolipids are the acylated glucosamine precursors of the lipid A component of the lipopolysaccharides in Gram-negative bacteria Typical lipid A molecules are disaccharides of glucosamine, which are derivatized with as many as seven fatty acyl chains 41 , Note that in naming these compounds, the total number of fatty acyl groups are counted regardless of the nature of the linkage i.

The minimal lipopolysaccharide required for growth in E. The Nod factors are oligosaccharides of glucosamine that are usually derivatized with a single fatty acyl chain. Additional saccharolipids include fatty acylated derivatives of glucose, which are best exemplified by the acylated trehalose units of certain mycobacterial lipids Acylated forms of glucose and sucrose also have been reported in plants Some saccharolipid structures are shown in Fig.

Polyketides are synthesized by classic enzymes as well as iterative and multimodular enzymes with semiautonomous active sites that share mechanistic features with the fatty acid synthases, including the involvement of specialized acyl carrier proteins 49 , 50 ; however, polyketide synthases generate a much greater diversity of natural product structures, many of which have the character of lipids.

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The class I polyketide synthases form constrained macrocyclic lactones, typically ranging in size from 14 to 40 atoms, whereas class II and III polyketide synthases generate complex aromatic ring systems Table Some polyketides are linked with nonribosomally synthesized peptides to form hybrid scaffolds. Examples of the three polyketide classes are shown in Fig. Many commonly used antimicrobial, antiparasitic, and anticancer agents are polyketides or polyketide derivatives.

Important examples of these drugs include erythromycins, tetracylines, nystatins, avermectins, and antitumor epothilones. Other polyketides are potent toxins. We consider this minimal classification of polyketides as the first step in a more elaborate scheme. It will be important ultimately to include as many polyketide structures as possible in a lipid database that can be searched for substructure and chemical similarity.

Bio Molecules - Lipids- Functions of lipids

The goals of the LIPID MAPS initiative are to characterize known lipids and identify new ones, to quantitate temporal and spatial changes in lipids that occur with cellular metabolism, and to develop bioinformatics approaches that establish dynamic lipid networks; the goals of Lipid Bank Japan are to annotate and curate lipid structures and the literature associated with them; and the goals of the European Lipidomics Initiative are to coordinate and organize scientific interactions and workshops associated with lipid research.

To coordinate the independent efforts from three continents and to facilitate collaborative work, a comprehensive classification of lipids with a common platform that is compatible with informatics requirements must be developed to deal with the massive amounts of data that will be generated by the lipid community. The proposed classification, nomenclature, and chemical representation system was initially designed to accommodate the massive data that will result from the LIPID MAPS effort, but it has been expanded to accommodate as many lipids as possible.

We also have attempted to make the system compatible with existing lipid databases and the lipids currently annotated in them. The development of this system has been enriched by interaction with lipidologists across the world in the hopes that this system will be internationally accepted and used. The authors appreciate the agreement of the International Lipids Classification and Nomenclature Committee to advise on future issues involving the maintenance of these recommendations. This committee currently includes Edward A.

The authors thank the Consortium for Functional Glycomics headed by Ram Sasisekharan at the Massachusetts Institute of Technology for providing us with their text nomenclature for glycosylated structures. We are grateful to Dr. Merrill Jr. Previous Section Next Section. View this table: In this window In a new window. TABLE 1. Lipid categories and examples. Representative structures for each lipid category.

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TABLE 2. TABLE 3. Shorthand notation for selected lipid categories. Fatty acyls [FA] The fatty acyl structure represents the major lipid building block of complex lipids and therefore is one of the most fundamental categories of biological lipids. TABLE 4. Fatty acyls [FA] classes and subclasses. Representative structures for fatty acyls. Glycerolipids [GL] The glycerolipids essentially encompass all glycerol-containing lipids. TABLE 5.

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Glycerolipids [GL] classes and subclasses. Representative structures for glycerolipids. Glycerophospholipids [GP] The glycerophospholipids are ubiquitous in nature and are key components of the lipid bilayer of cells. TABLE 6. Glycerophospholipids [GP] classes and subclasses. Representative structures for glycerophospholipids.

Sphingolipids [SP] Sphingolipids are a complex family of compounds that share a common structural feature, a sphingoid base backbone that is synthesized de novo from serine and a long-chain fatty acyl-CoA, then converted into ceramides, phosphosphingolipids, glycosphingolipids, and other species, including protein adducts 27 , TABLE 7. Sphingolipids [SP] classes and subclasses.

Representative structures for sphingolipids. Sterol lipids [ST] The sterol category is subdivided primarily on the basis of biological function. TABLE 8.

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Sterol lipids [ST] classes and subclasses. Representative structures for sterol lipids. Prenol lipids [PR] Prenols are synthesized from the five carbon precursors isopentenyl diphosphate and dimethylallyl diphosphate that are produced mainly via the mevalonic acid pathway TABLE 9. Prenol lipids [PR] classes and subclasses. Representative structures for prenol lipids.

TABLE Saccharolipids [SL] classes and subclasses. Representative structures for saccharolipids.