Dolichol derivatives

More recent studies of the growth of the branched structure of the mannan cores of glycopeptides, their dolichol-linked precursors and the metabolic inhibition of this, have reinforced the view that the first mannosyl transfer has an absolute requirement for GDPmannose and that this cannot be replaced by a dolichol derivative. The first mannosyl transfer differs from those that follow in the nature of the glycosyl donor and acceptor and in the anomeric configuration that is generated. 

Herscovics, A., Bugge, B. Jeanloz, R.W. (1977) Effect of Bacitracin on the Biosynthesis of Dolichol Derivatives in Calf Pancreas Microsomes, FEBS Letters, 82, 215-8... 

Leloir, L.F., Parodi, AJ. Behrens, N.H. (1971) Chromatography of Hydrophilic Residues of Dolichol Derivatives , Revista de la Sociedad argentina de biologia, 47, 108-16 L6toublon, R.C.P., Compte, J. Got, R. (1973) Transfer du mannose, a pertir de GDP-mannose a des accepteurs lipidiques chez Aspergillus niget, European Journal of Biochemistry, 40, 95-101... 

Forms by Dictyostelium discoideum Journal of Biological Chemistryy 257, 9861-5 Park, J.T. Johnson, M.J. (1949) Accumulation of Labile Phosphate in Staphylococcus aureus Grown in the Presence of Penicillin , Journal of Biological Chemistry, 179, 585-92 Park, J.T. Strominger, J.L. (1957) Mode of Action of Penicillin , Science, 125, 99-101 Paro, A.J. (1976) Protein Glycosylation Through Dolichol Derivatives in Baker s Yeast , FEBS Letters, 71, 283-6... 

Another compound of interest is dolichol which was first isolated from liver and is now known to be present in many other animal tissues. It is a long chain molecule (n=17-21), its first isoprene residue is saturated and it has 2 trans double bonds. It is found in liver part as the free alcohol and another part esteri-fied with fatty acids. We now know that a small amount is present as the phosphate or pyrophosphate and may have various sugars joined to it. These dolichol derivatives are involved in the glycosylation of proteins. An excellent review on polyprenols has been written by Hemming (1974). 

Sugar-aminoacid linkages. Various sugar-aminoacid linkages have been found in glycoproteins, some are formed directly by transfer from sugar nucleotides, others from dolichol derivatives and information is lacking for several of them. 

Figure26-2. Biosynthesis of squalene, ubiquinone, dolichol, and other polyisoprene derivatives. (HMG, 3-hydroxy-3-methylglutaryl x, cytokinin.) A farnesyl residue is present in heme a of cytochrome oxidase. The carbon marked with asterisk becomes C or C,2 in squalene. Squalene synthetase is a microsomal enzyme all other enzymes indicated are soluble cytosolic proteins, and some are found in peroxisomes.

The Css polyprenol (154) obtained from leaves of Magnolia campbelUi has been shown to be a mixture of cis- and /ran -isomers. The preparation of dolichyl phosphate (155) by a pea cell-free extract has been described. Evidence has been obtained that a lipid, containing 7V-acetylglucosamine, which was obtained from Phaseolus vulgaris hypocotyls, consists of a mixture of the dolichol (156) derivatives dolichyl pyrophosphate N-acetylglucosamine and dolichyl pyrophosphate di-N-acetylchitobiose. ... 

How, exactly, retinol affects protein glycosylation is not yet known, but the formation of retinol phosphate, the D-mannosylation of retinol phosphate by GDP-Man, and the transfer of Man from D-mannosyl (retinol phosphate) to pronase-sensitive glycoconjugates are well established.5857,59 On the other hand, the formation and role of other gly-cosyl esters of retinol phosphate are still controversial.2,80 It is very probable that the D-mannosylation of retinol phosphate, and also the transfer of Man from this lipid derivative to protein, are catalyzed by enzymes different from those involved in the dolichol pathway,81-83 and this finding points to the different physiological roles of Man-P-Dol and D-mannosyl (retinol phosphate). Thus, whereas Man-P-Dol can serve to D-mannosylate dolichol diphosphate-linked oligosaccharides (see Section III), such a role has not been found for D-mannosyl (retinol phosphate).81,83... 

Fig. 4.5.7 TLC analysis of short LLO. Fibroblasts derived from a control (lane 1, left) andaCDG-Ii patient (lane 2, right) were metabolically labelled for 30 min with [2-3H] mannose. Short LLO were extracted with chloroform/methanol (3 2) and further analysis carried out by TLC in a running buffer containing chloroform/methanol/LLO (65 25 4). The position of the origin, and the positions of [3H]ManiGlcNAc2-PP-dolichol and [3H]Man2GlcNAc2-PP-dolichol are indicated...

The synthesis of N-linked glycosides also occurs in the lumen of the ER and in the Golgi. However, these structures undergo additional processing steps, and require the participation of a lipid (dolichol) and its phosphorylated derivative, dolichol pyrophosphate (Figure 14.16). 

Grange and Adair73 isolated 2,3-dehydrodolichyl phosphate from in vitro studies on hen oviduct. It may be derived from 2,3-dehydrodolichyl diphosphate, a likely intermediate in the biosynthesis of dolichyl phosphate. Many questions still remain unanswered, such as is the substrate for the a-isoprene reductase, the diphosphate or the monophosphate of 2,3-dehy-drodolichol Are the unsaturated polyprenols a reserve pool for the synthesis of dolichol in plants What is the function of unsaturated, plant polyprenols How is the synthesis of saturated and unsaturated polyprenols regulated ... 

The concentration of dolichyl phosphate in eukaryotic tissues is very low and is probably rate-limiting for the glycosylation processes. Variation of the concentration in the endoplasmic-reticulum membranes is a possible way of controlling the rate of glycosylation. It is important to point out that the early steps in the dolichol biosynthesis are common to such other prenyl derivatives in plants as steroids, essential oils, hormones, phytol, and carotenes (see Scheme 1), and parameters affecting those reactions that may control the dolichol to dolichyl phosphate step could be another mechanism for regulation of the level of dolichyl phosphate. 

W.R. Schaffer (University of California, Berkeley) and colleagues have been investigating what are known as isoprenoids. These compounds are stiuctuially related lipophilic molecules that peifonn a wide variety of essential cellular functions, These lipids include such functionally diverse molecules as cholesterol, ubiquinone, dolichols. and chlorophyll, yet isoprenoids are derived from a common precursor, mevalonic add. These studies may lead to a better understanding of the Ras oncogenic proteins,... 

A second method that we considered involved condensation of a carbohydrate-derived phosphate salt with an in situ-generated phosphoryl dichloride.21 The requisite phosphoryl dichlorides are prepared via exposure of a lipid phosphate to a Vilsmeier-type reagent. This protocol has been used successfully for the preparation of lipid diphosphate linkages in the dolichol series (i.e., lipids lacking an allylic double bond proximal to the diphosphate linkage). However, we were once again, hesitant to expose our undecaprenyl phosphate precursor to activation conditions that produce HC1 as a by-product. 

Terpenes and steroids are biosynthetically derived from mevalonate. They can be hydrocarbons, e.g. carotene, alcohols, e.g. dolichol, esters, e.g. do-licholphosphate, or cholesterol esters, and others. Cholesterol is essential for membrane function in higher animals. 

The asparaginyl glycoproteins are synthesized through the use of dolichol phosphate, a member of the isoprenoid family, which is attached through its hydrophobic residue to endoplasmic reticulum. Other isoprenoid compounds or their derivatives are natural rubber, the steroids, including cholesterol, and vita-... 

In addition to vitamin E, the isoprenoids and their derivatives up to cholesterol give rise to all the fat-soluble vitamins (A,D,E,K) and to coenzyme Q (used in electron transport in the Ferris Wheel Generator). Dolichol is an isoprene polymer that participates in the transfer of oligosaccharides during glycoprotein synthesis. 

No I all cofaclyrs are derived from vitamins, Coenzyme Q, lipoic acid, dolichol phosphate, biopterin, heme, and molybdopterin are cofactors that are synthesized in the body from simple organic compounds. Heme and molybdopterin are relatively complex, from a nutritional point of view, because they require metal ions as part of their structure. 

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