Bactoprenol phosphate

Step 1 Assembiy of NAG-NAM on bactoprenol phosphate inside the ceil... 

Step 4 Addition of NAM-p to bactoprenol phosphate for assembly of the repeating NAG-NAM-decapeptide and transport through the membrane and Insertion into the chain as in Step 2. 

An interesting aspect of the biosynthesis of the O-antigen polysaccharide is that different nucleotide triphosphates are the activating agents for each of the monosaccharide residues in the repeating unit. The reaction of UDP-Gal with bactoprenol phosphate is the first reaction in the process, followed by reactions with TDP-Rha, GDP-Man, and CDP-Abe as shown for the biosynthesis of Salmonella typhimurium O-antigen polysaccharide summarized in Fig. 10.12A. 

FIGURE 8.18 Dolichol phosphate is an initiation point for the synthesis of carbohydrate polymers in animals. The analogous alcohol in bacterial systems, undecaprenol, also known as bactoprenol, consists of 11 isoprene units. Undecaprenyl phosphate delivers sugars from the cytoplasm for the synthesis of cell wall components such as peptidoglycans, lipopolysaccharides, and glycoproteins. Polyprenyl compounds also serve as the side chains of vitamin K, the ubiquinones, plastoquinones, and tocopherols (such as vitamin E). 

Insertion of monomer units at the base of a chain is a major mechanism of polymerization that is utilized for synthesis not only of polysaccharides but also of proteins (Chapter 29). For most carbohydrates the synthesis is dependent upon a polyprenyl lipid alcohol, hi bacteria this is often the 55-carbon undecaprenol or bactoprenol,136 which functions as a phosphate ester ... 

Undecaprenol (bactoprenol) from Salmonella contains eleven isoprene units, and two irons and nine cis double bonds In the form of undecaprenyl phosphate, it acts as a carrier of carbohydrate residues in the biosynthesis of bacterial antigenic polysaccharides synthesis of Murein (see) also depends on undecaprenyl phosphate. In eukaryotes the Dolichol phosphates (see) function in the transfer of carbohydrate residues in the synthesis of glycoproteins and glycoli-pids. Probably the long lipid chains of these P serve to anchor them in membranes, while the phosphate group acts as a carrier by protruding into the cytoplasm. It is not known whether all P. function as carbohydrate carriers. The structural relationship between solanesol and plastoquinone-9 and ubiquinone-9, and the joint occurrence of these compounds suggest a precursor role for P. Biosynthesis of P. proceeds from mevalonic acid and the conformation of all double bonds is predetermined in early precursors. 

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