Murein sacculus

Proteins identified by their ability to bind labelled (3-lactam antibiotics in vivo and in vitro. The intrinsic activities of PBPs include transglycosylase/transpepti-dase, carboxypeptidase and endopeptidase activities required for the formation of the bacterial murein sacculus forming the bacterial cell wall. The enzymes are located in the cytoplasmic membrane. 

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]. 

Holtje, J. Y. (1998). Growth of the stress-bearing and shape-maintaining murein sacculus of Escherichia coli, Microbiol. Mol. Biol. Rev., 62, 181-203. 

A latex of poly(/3-hydroxyoctanoate) can be obtained from the bacterium Pseudomonas oleovorans grown on sodium octanoate at a high cell density (22). In the course of purification sodium hypochlorite was used. It was observed that latex stabilization occurred spontaneously due to the persistence around the polymer granules of the murein sacculus, which envelopes the bacterial ceU. It was shown that the optimal conditions for the bacteria digestion correspond to a sodium h ochlorite concentration of 21-26 mmolg. ... 

Fig. 337. Part of the murein sacculus of the bacterial cell wall...

Besides the murein sacculus, many bacteria also produce other polysaccharides that surround and are exterior to the murein cell wall. These polysaccharides serve various purposes in protecting the cell from lysis, virus infection, and changes in the environment including pH, temperature, and concentrations of oxygen. These materials are compact and can be microscopically observed surrounding the cell. They are called capsules. Other bacteria produce more diffuse polysaccharides that also are extracellular but are not so intimately associated with the cell. These less-defined polysaccharides are often called slimes. The dextrans make up such materials. 

Cell envelopes of archaea diifer distinctly from those of bacteria and show remarkable structural and chemical diversity. Murein, the typical sacculus-forming polymer of bacteria, and lipopolysaccharide-containing outer membranes, characteristic of gramnegative bacteria, are not found in archaea. Crystalline surface layers (S-layers) are common in both prokaryotic domains and they consist of protein or glycoprotein subunits (Table 1). However, S-layers in archaea have a form-stabilizing function especially when they are the only envelope layer outside the cytoplasmic membrane, while in bacteria S-layers have no distinct form-stabilizing function. 

The lack of a murein cell-wall sacculus and the discovery of different cell-envelope polymers and structures in some physiologically unusual prokaryotes, was one of the first biochemical and cytological evidences in favour of Carl Woese s archaebacteria concept [46,149,150]. Since then, increasingly more unique cell-envelope polymers and new types of biosynthetic pathways have become known. These findings corroborate the proposal that the archaea represent a third lineage of organisms [150] in addition to bacteria and eucarya, and that the common ancestor or ancestral population of the archaea did not evolve any cell-wall polymer before it radiated into the various sublineages known today [46,151]. 

The peptidoglycan murein forms a sacculus which shapes the bacterial protoplas. (E 2.2). It is a kind of a exoskeleton. 

Leutgeb, W., Schwarz, U. Zur Biosynthese des formgebenden Elements der Bakterien-zellwand. I. Abbau des Mureins als erster Schritt beim Wachstum des Sacculus. Z. Naturforsch. 22b, 545-549 (1967). 

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