Peptidoglycan or murein

Schematised electron transfer pathway across a Gram-negative bacterial ceU membrane (with lactate as the primary electron donor), coupled with H translocation and ATP synthesis, adopted and simplified from ref. 137. MQ and MQHj are menaquinone and -hydroquinone, respectively CymA is a tetrameric and MtrC a decameric cytochrome-c type haemoprotein. See also the text and Eqnation (4.41)). Peptidoglycan (or murein), serving a structural role in the cell membrane, is a block copolymer built up from acetylhexoses and oligopeptides.

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... 

Archaebacterial cell wall composition can vary markedly between species. The cell walls of some species contain only protein, whereas others comprise glycoprotein, polysaccharide or a type of peptidoglycan, but murein is never present.The Gram stain test can also be applied to archaebacteria (e.g. Halobacterium are Gram-negative). 

Figure 43-2. Beta-lactams and bacterial cell wall synthesis. The outer membrane shown in this simplified diagram is present only in gram-negative organisms. It is penetrated by proteins (porins) that are penrie-able to hydrophilic substances such as beta-lactam antibiotics. The peptidoglycan chains (mureins) are cross-linked by transpeptidases located in the cytoplasmic membrane, closely associated with penicillinbinding proteins (PBPs). Beta-lactam antibiotics bind to PBPs and inhibit transpeptidation, the final step in cell wall synthesis They also activate autolytic enzymes that cause lesions in the cell wall. Beta-lactamases, which inactivate beta-lactam antibiotics, may be present in the periplasmic space or on the outer surface of the cytoplasmic membrane. (Reproduced, with permission, from Katzung BG [editor]. Basic Clinical Pharmacology, 8th ed. McGraw-Hill, 2001.)...

Structurally related to sialic adds is N-acetylmuramic add (4-104), the building unit of peptidoglycans of baderial cell walls or mureins. 

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. 

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. 

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

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. 

TddMronicaclds. Poly saccharides, which may contain uronic acids (e.g., D- glucuronic acid or N-ace-tyl-D-mannosaminuronic acid), isolated from the cell walls (hence the name, from Greek teichos=wall) of Gram-positive bacteria. T. a. are either linked directly or via oligosaccharides to the peptidoglycan (murein) of the cell wall. 

The cell walls (Section 9.1) of bacteria contain substances called mureins or peptidoglycans, the latter being the preferred name. The polymeric backbone of peptidoglycans is structurally close to chitin (Section 3.6), being composed of -acetyl-D-glucosamine and its 3-lactyl derivative, A -acetyl-muramic acid which are linked together by 3-(l- 4) bonds (Figure 3.10a). Chains of this struc-... 

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