Murein-peptidoglycan

Figure 10. Schematic view of the uptake of ferric siderophores by Gram-positive and Gram-negative bacteria. Please note that the murein (peptidoglycan) network associated with the cytoplasmic membrane is not shown. For details see text...

Principles to stabilize lipid bilayers by polymerization have been outlined schematically in Fig. 4a-d. Mother Nature — unfamiliar with the radically initiated polymerization of unsaturated compounds — uses other methods to-stabilize biomembranes. Polypeptides and polysaccharide derivatives act as a type of net which supports the biomembrane. Typical examples are spectrin, located at the inner surface of the erythrocyte membrane, clathrin, which is the major constituent of the coat structure in coated vesicles, and murein (peptidoglycan) a macromolecule coating the bacterial membrane as a component of the cell wall. Is it possible to mimic Nature and stabilize synthetic lipid bilayers by coating the liposome with a polymeric network without any covalent linkage between the vesicle and the polymer One can imagine different ways for the coating of liposomes with a polymer. This is illustrated below in Fig. 53. 

The murein-peptidoglycan gives rigidity and different specific shapes, such as rods, spheres, or spirals to bacterial ceUs. Because of the cross-linking of the murein chains, the peptidoglycan is considered one giant, bag-shaped macromolecule [91]. The stmctures of segments of chitin, chitosan, and murein are shown in O Fig. 6. 

A-Acetylmuramic acid (D-MurpAc) HO COOH NHCOCH3 iV-Acetylmuramic acid is 2-acetamido-2-deoxy-3-0-[(R)-l-carboxyethyl]-D-glucose. MurAc and GlcNAc alternate via P-1 4 linkages in murein (peptidoglycan) of bacterial ceU wall. 

The cell walls of gram-positive bacteria are formed from peptidoglycan (synonymous with murein). Peptidoglycan consists of repeating units of the disaccharide N-acetylglucosamine... 

The essential genetic material ofthe original vegetative bacterium is retained in the core or protoplast around this lies the thick cortex which contains the murein or peptidoglycan already encountered as a cell wall component (see Fig. 1.2). The outer coats which are protein in composition are distinguished by their high cysteine content. In this respect they resemble keratin, the protein of hair and horn. 

Also in the PP, associated with the CM, one can find the murein sacculus (for a review see [8]). This network is formed by the macromolecule pepti-doglycan, which confers the characteristic cell shape and provides the cell with mechanical protection. Peptidoglycans are unique to prokaryotic organisms and consist of a glycan backbone of N-acetylated muramic acid and N-acetylated glucosamine and cross-linked peptide chains [9-13]. 

The main component of bacterial cell membranes is a mixed polymer known as murein or peptidoglycan. Peptidoglycan is a long polysaccharide chain that is cross-linked with short peptides. 

The (3-lactam antibiotics structurally resemble the terminal D-alanyl-D-alanine (o-Ala-o-Ala) in the pen-tapeptides on peptidoglycan (murein) (Fig. 45.1). Bacterial transpeptidases covalently bind the (3-lactam antibiotics at the enzyme active site, and the resultant acyl enzyme molecule is stable and inactive. The intact (3-lactam ring is required for antibiotic action. The (3-lactam ring modifies the active serine site on transpeptidases and blocks further enzyme function. 

Peptidoglycans (14,16) are the primary component of bacterial cell walls. They consist of a heteropolysaccharide called murein cross-linked with short peptide chains. 

SRRz Bacteriophage X lysis gene cluster S Creates lesions in cytoplasmic membrane R Transglycosylase, degrades murein Rz Cleaves peptidoglycan cross links Kloos et al. (1994)... 

The complex structure of bacterial cell walls is discussed in Chapter 8. However, it is appropriate to mention a few bacterial polysaccharides here. The innermost layer of bacterial cell walls is a porous network of a highly crosslinked material known as pepti-doglycan or murein (see Fig. 8-29). The backbone of the peptidoglycan is a P-l,4-linked... 

The fatty acid chains are evidently embedded in the outer membrane as an anchor. About one-third of the lipoprotein molecules are attached covalently to the peptidoglycan through an amide linkage between the side chain amino group of the C-terminal lysine of the protein and a diaminopimelic acid residue of the peptidoglycan (Fig. 8-29). Thus, the protein replaces one of the terminal D-alanine residues of about one in ten of the murein peptides. There are 2.5 x 105 molecules of the bound form of the lipoprotein per cell spread over a surface area of peptidoglycan of 3 pm2. They appear to be associated as trimers located primarily in the periplasmic space.589... 

Figure 8-29 (A) Repeating unit of structure of a bacterial peptidoglycan (murein). Some connecting bridges are pentaglycine (Staphylococcus aureus), trialanylthreonine (Micrococcus roseum), and polyserine (S. epidermis).

Multidrug resistance protein 417 Multilamellar vesicles (liposomes) 392 Multiple attack concept 606 Multisubstrate enzymes, kinetics of 464 Muramic acid (Mur) 165s Murein 170,428,429s. See also Peptidoglycan Musci 29 Muscle(s)... 

The outer surfaces of bacteria are rich in specialized polysaccharides. These are often synthesized while attached to lipid membrane anchors as indicated in a general way in Eq. 20-20.136/296a One of the specific biosynthetic cycles (Fig. 20-9) that depends upon undeca-prenol phosphate is the formation of the peptidoglycan (murein) layer (Fig. 8-29) of both gram-negative and gram-positive bacterial cell walls. Synthesis begins with attachment of L-alanine to the OH of the lactyl... 

Cell wall Peptidoglycan (murein or mucopeptide) as component Absence of peptidoglycan... 

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