Types of Lipids III

Suaib Luqman

epgp books

 

 

  1. Objectives
  • v To know about the complex lipids
  • v What are the significance of glycolipids
  • v How they act in a system

 

  1. Concept Map

 

  1. Description

3.1 Types of Lipids III

 

Complex Lipids

 

 

Glycolipids

 

 

In Mycobacteria L

and holds key significance in the interaction between host and pathogen. This phosphatidylinositolglycans demonstrates the earliest version from prokaryotes branded for cell surface protein anchoring and the lipoarabinomannan structural features have been used across the globe as tuberculosis vaccine.

The surface of Leishmania, Entamoeba and Crithidia contains Lipophosphoglycan, a Glycolipid serene with four domains: (1) an alkyl lyso phosphatidylinositol (2) core of glycan (3) Repeated units of Gal-Man-PO4 backbone and (4) Cap structure of an oligosachharide has been involved in a numerous functions inside the mammalian host.

In the strains of Streptococcus sp., Glucopyranosyl cardiolipin (Glycosylated cardiolipin) was initially noticed and identified (18% of the lipid phosphorus) but present as a trifling constituent in Vagococcus fluviatilis.

 

X = glucosyl residue

 

 

This infrequent glycolipid was also reported in Geobacillus steathermophilus (4% of total phospholipids) acylated primarily by oleic acid (~ 25%) and palmitic acid (~ 33%). Revealed predominantly as iso-C15:0 and anteiso-C17:0, this composite might be implicated in the subvert effect of high temperature on the membrane organization and in the regulation of lipid composition of G. stearothermophilus. In Deinococcus radiodurans, 3-(galactopyranosyl)-2-(3-phosphatidyl) glyceroyl derivative, an exclusive glycophospholipid of a fatty alkylamine (~ 33% of the total lipids) has also been identified.

 

The R3 (alkylamines) are generally straight chain compounds (C15-C17 or C16-C18), with isomeric 17:1 bases preponderant.

A phosphocholine-containing glycoglycerolipid has been reported to be produced by Mycoplasma fermentans in which the phosphocholine assembly is attached to the C6 of glucose moiety. This lipid valor in the pathogenesis of rheumatoid arthritis by eliciting cell death or inflammation through their phosphocholine dregs.

 

(Acyl: fatty acyl group, Glcp: glycero-1-phospho, Ptd: 3-phosphatidyl)

In Staphylococcus membranes, additional complex phosphorylated compounds lipoteichoic acids contains polymer of glycerol-1-phosphate allied to a glycosyl diglyceride or a phosphatidyl glycosyl diglyceride is present. Other swapping on the glycerophosphate units with alanyl or glycosyl groups has also been reported

Structure of lipoteichoic acid from Bacillus subtilis where R1 and R2 are acyl group of fatty acid and R3 is mainly acetylglucosaminyl, alanyl or H.

Sulfoglycoglycerolipids

Are lipids demeanoring a sulfur atom found in acidic membranes with a strong acidic pH (~2), is present in some mammalian cells, chloroplast of higher plants, bacteria, algae and in fungi. This type of lipid has also been described in Elakatothrix and Zygnema, green alga and in Fucus, Pelvetia. At very low pH, carboxylic acids occur in unionized forms, but sulfolipids subsist in the anionic form. In Chlorella, a new type of sulfolipid (sulfoquinovosyl diacylglycerol: SQDG) derived from MGDG was discovered in 1959 at the Scripps Institute of Oceanography (San Diego, CA, USA) which was afterward described in the thylakoid membranes of all higher and lower plants. Hence, sulfolipids are present algae, cyanobacteria, few basidiomycetes fungi (Clitocybe, Coprinus, Psalliota) and photosynthetic membranes of plants,.

The biological function and mechanism for SQDG biosynthesis has been described in higher plants predominantly under phosphate ravenous circumstances. SQDG is the lipid with a sulfonic acid link, containing MGDG at C6 position of the monosaccharide unit, sulfoquinovosyl (quinovose : 6-deoxy-D-glucose) is the sulfonoglucosidic moiety (6-desoxy-6-sulfono-glucoside), R1 is often the palmitic acid and R2 is the unsaturated chain (16:3 n-3).

Heterosigma carterae (Raphidophyceae), a marine chloromonad was revealed to include a intricate mixture of SQDG. The major fatty acyl groups contain 20:5 (n-3), 16:1 (n-3), 16:1 (n-5), 16:1 (n-7) and 16:0. In Rhizobium meliloti, a symbiotic bacterium as well as in other strains of Rhizobiaceae, existence of SQDG has been established. The occurrence of SQDG outside the plant kingdom suggested the role of sulfolipid in the Rhizobium/legume relationship. In Halobacterium, sulfate esters are reported with two alkyl diphytanylether chains. SQDG type bearing mono-unsaturated (20:1 to 24:1) and saturated (14:0 to 24:0) fatty acids were also extorted from a sea urchin (Scaphechinus mirabilis). Gustafson et al (1989) reported anti HIV-1 activity of SQDG from cyanobacteria containing linolenic and palmitic acids. Sulfate esters of

 

galactoglycerolipids are reported in quite a few mammalian tissues like brain, testis, spermatozoa (3% of total lipids, >90% of total glycolipids in mammalian testis and ~0.3-1 mmole/g). The acyl groups R’ and R” are most frequently saturated (16/18 carbon atoms).

Seminolipids, mixture of alkylacyl and DAG is associated with myelination process of the nervous system (Pieringer J et al., 1977, 166, 421). They are also essentail for mice spermatogenesis. From Hyphomonas jannaschiana, a sea water bacterium, a tauroglycolipid has been isolated lacking phospholipids. The structure determined as 1,2-diacyl-3-glucuronopyranosyl-glycerol taurine-amide with 16:0, 16:1 n-7, 18:0, 18:1 n-7 and 19:0 as major acyl chains.

 

i. Ceramides based Glycolipids:

 

Out of 150 known varieties in this cluster of glycosphingolipids, 50 categorized into the structure of ganglio. Strewned mostly at the surface of the cell, they participate in the regulation of cell interactions and dole out as distinctive markers for cells and mediate cell to cell detection and contact. Ceramides based glycolipids are vital for the growth and development of organisms and allude to viral or microbial infections and cancer. They form molecular complex named ‘Glycosynapse’ and helps in explicit recognition between cells function and signaling. They are found in animals, bacteria, fungi, and plants. The grouping of glycosphingolipids is based on the structure of the carbohydrate moiety and is as under:

 

·         Neutral glycosphingolipids (unsubstituted glycosyl group)

 

It includes single or extra glycosyl moieties, hexoses (sometimes pentose) and an added hexosamine. As per the presence of glycosyl units they may be one glycosyl unit (monoglycosylceramides), more than one glycosyl units (oligoglycosylceramidest) or other structure containing only one glycosylated sphingoid base (deacylated glycosphingolipids), one fatty acid linked to cerebrosides (acylated glycosphingolipids), complex sphingolipids with a ceramide containing a cyclopropane chain and prenylated residues on galactose (plakosides).

 

·         Acidic glycosphingolipids

 

Are zwitterionic molecules with glycosyl and carboxyl group, sulfate or phosphate. Examples are gangliosides (a carboxyl group on sialic acid and several glysosyl residues), acidic monoglycosylceramides, phosphonoglycosphingolipids, sulfosphingolipids (ceramide di & tri hexosyl sulfate with one sulfate moeity on the glycosyl unit, sulfatides), phosphosphingolipids (phosphorylceramide with oligosaccharide or glycosyl head moeity).

 

 

ii. Lipopolysaccharides (LPS)

 

Are the endotoxin (endotoxic-o-antigens) emanated from the cell walls of Gram negative bacteria and in a fungus (Antrodia camphorata). Due to their nature, they may cause numerous pathophysiological symptoms like blood pressure decrease, diarrhea, fever, septic shock and death. There are three parts in LPS, part A (Lipid A) silhouette a composite with part B (polysaccharide core) through a glycosidic linkage which is allied to an external area of part C (an immunogenic and capricious polysaccharide chain or antigen composed up of repeating oligosaccharide units liable for the specificity of bacterial serological strain. Part A (Lipid A) includes a backbone of b 1, 6-glucosaminylglucosamine with two phosphoester moiety at position 1 of glucosamine I and in position 4 of glucosamine II. The position 3 of glucosamine

  • II assembles the glycosidic linkage (acid labile) to the polysaccharide chain. In coli, the supplementary groups are replaced with fatty acids ((hydroxylated) as hydroxymyristate (two amide & two ester linked) and laurate (fatty acid). In the same species, the LPS fatty acid profiles vary distinctly from the phospholipids.

3-hydroxyalkanoic acids and 2-hydroxyalkanoic acids are common hydroxylated fatty acids but some bacteria (Achromobacter, Bacteroides, Brucella, Gardnerella, Sorangium, Thermus, Thiobacillus) lacks hydroxy acids. Even carbon compounds (12-18 atoms) containing hydroxy acids are straight-chain while odd-carbon acids are minor components (13-17 atoms) of Bordetella, Pseudomonads, Pectinatus, Selenomonas, Vibrio and Veillonella. In Capnocytophaga, Flavobacterium, Desulfovibrio, Legionella, Pseudomonas and Moraxella, species a specialized branched chain hydroxy fatty acids (3OH i 11:0 up to3OH i 17:0) has also been reported. In Pseudomonas and Azospirillum species, a small number of unsaturated hydroxy fatty acids have been depicted, except the presence of 2OH, 18:1. Listeria monocytogenes, an infective agent in milk, is the solitary Gram positive bacteria that acquire LPS where the polysaccharide is non-toxic and the toxic activity is attributed to the part

A (Lipid A) that causes septic shock. The subsistence of LPS was established in a fungus (Antrodia camphorate) of Polyporaceae family revealing fucose, glucose, galactose and sorbitol in LPS, galactosamine and glucosamine were deficient. Furthermore, the sequestered compound showed some anti-inflammatory effect and a low cytotoxicity. An efficient method using hot ammonium isobutyrate solvent for the extraction of LPS and sequestration of lipid A from bacteria has been described. Lipid X a closely related precursor of lipid A has also been portrayed revealing various pharmacological properties.

 

 

iv.   Sterol based Glycolipids:

 

They occur as free sterols, esters (acylated), alkyl ethers (alkylated), sulfated or linked to a steryl glycoside moiety. The biosynthesis of sterol is everpresent amid eukaryotes but almost wholly deficient in prokaryotes. Being absent in Archaea, they are sparingly distributed in bacteria and Methylococcus capsulatus (proteobacterium), Gemmata obscuriglobus (planctomycete) along with myxobacteria members. As a consequence, the existence of varied steranes (saturated 4 cycle skeleton) in primordial rocks is used as proof for eukaryotic evolution somewhere 2.7 billion years ago.

 

The sterols have hopanoids as precursor and an oxygen-dependent biosynthesis starting with the creation of 2, 3-oxidosqualene (primary intermediate). Hence, steroid and triterpenoid hydrocarbon detection in the history of Earth has been used to surmise the relic of oxygenic photosynthesis. It has been conjecture that levels of oxygen increased in the atmosphere made the sterols evolution feasible and make possible the eukaryotes birth giving them with an untimely protection mechanism against oxygen.

 

Free Sterols

 

Sterols (Greek: stereos-solid) shape an imperative cluster amid steroids. The unsaturated

 

steroids involve a 3b-hydroxyl group (cholestane skeleton) and carbon atoms (8 or more) of an aliphatic side chain at position 17 figuring the group of sterols. Being saponification resistant, they are endowed in all animal and vegetal tissues important in the appraisal of marine sediment maturity as a biological marker compound, yet past hundreds millions years. They also comprise 3-hydroxysteroids (C27 to C30) crystalline alcohols and are classed as triterpenes (being derived from squalene) directly by unsaturation, cyclization and 3b-hydroxylation, cycloartenol in plants or lanosterol in animals.

 

 

5a-cholestane

 

  1. Summary

 

In this lecture we learnt about:

 

  • The Types of Glycolipids
  • Their benefit & advantages
you can view video on Types of Lipids III

 

Weblinks

 

 

Books

 

  1. Glycolipids, Phosphoglycolipids, and Sulfoglycolipids by Kates M. 2013. Page 1. https://books.google.co.in/books?isbn=1489925163
  2. Handbook of Lipid Bilayers by Marsh D. 2013. Second Edition – Page 863 https://books.google.co.in/books?isbn=1420088335
  3. Bacterial Lipopolysaccharides: Structure, Chemical synthesis, Biogenesis and interaction with host cells by Yuriy A. Knirel, ‎Miguel A. Valvano. 2011. https://books.google.co.in/books?isbn=3709107334
  4. Chemistry Of Biomolecules by Bhutani SP. 2009. Page 258 https://books.google.co.in/books?isbn=8190840657
  5. Biochemistry by Berg JM, Tymoczko JL, Stryer L. 2002. 5th edition. New York: W H Freeman; 2002. http://www.ncbi.nlm.nih.gov/books/NBK22361/
  6. Teaching Innovations in Lipid Science by Randall J. Weselake. 2007. Pages-216 https://books.google.co.in/books?isbn=1420012800