Murein synthesis

EJJ Lugtenberg, L de Haas-Menger, WHM Ruyters. Murein synthesis and identification of cell wall precursors of temperature-sensitive lysis mutants of Escherichia coli. J Bacteriol 109 326-335, 1972. 

Alice et al studied the turnover kinetics of Listeria OTonocytogenex-secreted p60 protein (a murein hydrolase) by host cell cytosolic proteasomes. J774 cells, seeded in flasks and incubated overnight in culture medium, were infected with log-phase cultures of E. monocytogenes for 30 min, washed, and incubated in culture medium for 3 h, with gentamicin (50 tg/ml) added after the first 30 min to inhibit extracellular bacterial growth. Cells then were washed and placed in methionine-free medium with spectinomycin, gentamicin, the eukaryotic protein synthesis inhibitors [cycloheximide (50 tg/mL) and anisomycin (30 tg/ml),] and 25 dVI calpain inhibitor I. After 30 min, [ S]methionine was added, and the cells were pulse-labeled for periods of 20 to 60 min. Cells... 

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... 

UDP-GlcNAc represents the branching point for the bacterial biosynthesis of murein and lipopolysaccharides where secondary nucleotide sugars are involved [329, 358], Starting from fructose-6-P, all enzymes are available as recombinant proteins and enzymatic synthesis of important intermediates seems to be possible. 

An understanding of the biochemistry of peptidoglycan (PG murein) that comprises bacterial cell walls is very important medically since blockage of its synthesis was the first, and continues to be a primary, point of attack in the control of bacterial infection. In addition to inhibition of cell wall synthesis, antimicrobial drug s main mechanisms are interference with nucleic acid synthesis, inhibition of folate metabolism, and binding to ribosomes to disrupt protein synthesis (Table 16-2). 

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.

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.)...

Mechanism of action In cell wall synthesis B. acts as an inhibitor of the biosynthesis of murein. 

Arendt, a., a. Kolodziejezyk, and T. Sokolowska Synthesis of mucopeptide fragments of bacterial cell walls containing diaminopimelic add. Part IX. Synthesis of pentapeptide related to bacterial mureine fragment. Roczniki Chem. Ann. Soc. Chim. Polonorum. 48, 1921 (1974). 

Maturation of ConA precursor. Pulse-chase experiments with radioactive amino acids strongly support a mechanism of transpeptidation, rather than proteolytic cleavage followed by ligation. The only other known precedent for such a mechanism is the last step of peptidoglycan synthesis in bacteria (see Murein). Inspection of possible three-dimensional structures of Con A and its precursor show that maturation by transpeptidation is possible without unfolding of the polypeptide chain. 

Uridine diphosphate Glucose Involved generally in carbohydrate metabolism. Glycogen (see) synthesis. Murein (see) synthesis. 

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. 

Vancomycin is a broad spectrum antibacterial, which acts to inhibit the construction of the bacterial cell wall by forming a complex with o-alanyl-D-alanine, required for the synthesis of an essential membrane protein, murein. The antibiotic is administered by infusion and is most commonly used to treat infections with organisms that are resistant to other commonly used antibacterials. Today, this is frequently the case with Gram-positive bacteria such as Staphylococcus aureus. 

An efficient synthesis of (benzyl 4,6-0-benzylidene-A-acetylmuramyl)-L-alanine is shown in Scheme 4 this compound is a key intermediate in the synthesis of mucopeptides. The synthesis of A -acetylmuramyl-L-alanyl-D-/5o-glutamyl-LL-diaminopimelyl-D-alanine, a glycopeptide constituting part of the structure of the mureines of two bacteria, has been reported. ... 

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