Bacterial cell wall glycosylation

Cycloserine (Fig- 4) is produced by several species of Streptomyces. One of the basic glycosyl components of the bacterial cell wall, n-acetyl-muramic acid (the product of Mur A and MurB), is modified by the addition of the first three amino acids sequentially by MurC, MurD and MurE enzymes. A dipeptide, D-alanyl-D-alanine is then added to make the pentapeptide. In bacteria, L-alanine is the native form and it is converted to D-alanine form by alanine racemase (Air). Two D-alanines are joined by D-ala-D-ala ligase (DdlA) to synthesize the dipeptide. Cycloserine resembles the substrate for Air and Ddl and inhibits their respective reactions in stage I of the peptidoglycan biosynthesis (Fig. 2). 

Sofia et al. (41) reported a SP library of disaccharides L7 made by 1300 individuals and inspired by the disaccharide core of moenomycin A, a bacterial cell wall inhibitor (Fig. 4.8). Both the structure of the library and its main features are shown in Fig. 4.8. The four major disaccharide scaffolds (X, Y, and W variations) were either built on resin via glycosylation or attached onto the photolabile linker, and subsequently decorated by introduction of Ri, R2, and R3 radiofrequency encoding (42) was used to obtain a large number of discretes with an affordable number of reactions. The... 

The role of undecaprenyl phosphate (C55, allylic) as a carrier of glycosyl units in the biosynthesis of bacterial cells walls is well established. Dolichyl phosphate plays a similar role in the synthesis of glycoproteins in animal systems. Evidence that prenyl lipids serve as glycosyl carriers in the biosynthesis of glycoproteins in plants is accumulating rapidly (Pont Lezica et al., 1976 Delmer al., 1978 Erickson et al., 1978). Several authors have recently reviewed the literature on the role of polyprenols as glycosyl carriers in plants (Hemming, 1978 Pont Lezica, 1979 Elbein, 1979). 

Among the long-chain proline-rich AMPs, diptericin that is carrying post-translational modifications (C-terminal amidation and two O-glycosylations, see for details the previous section of this chapter) has a controversial mode of action. It was shown to disrupt the bacterial membrane, but it is unlikely that it acts primarily as a pore-former, rather it is expected to target metabolic processes such as nucleic acid, protein, and cell wall synthesis [98]. 

The functions of lipid intermediates in the biosynthesis of a man-nan, a bacterial capsular polysaccharide, a cell-wall lipopolysac-charide, and a cell-wall peptidoglycan are respectively discussed in Sections dealing with each (see Sections V,6, p. 396 VI,5,6, and 7, pp. 408, 418, 428). In all these syntheses, the glycosyl groups are... 

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