Peptides Peptidoglycan

The humin components isolated in DMS0/H2S04 media contain macromolecular components, such as peptides, peptidoglycans, and possibly mucopolysaccharides (Simpson et al., 2007), and these would appear to be strongly sorbed to the soil inorganic colloids. Such species can therefore be considered to have importance in soil particle interactions. 

Cell wall Peptidoglycan a rigid framework of polysaccharide cross-linked by short peptide chains. Some bacteria possess a lipopolysaccharide- and protein-rich outer membrane. Mechanical support, shape, and protection against swelling in hypotonic media. The cell wall is a porous nonselective barrier that allows most small molecules to pass. 

Figure 6.7 Formation of cross-linkage between individual peptide chains in the peptidoglycan layer of S. aureus.

Penicillin has an interesting mode of action it prevents the cross-linking of small peptide chains in peptidoglycan, the main cell wall polymer of bacteria. Pre-existing cells are unaffected, but all newly produced cells are abnormally grown. The newborn cells are unable to maintain their wall rigidity, and they are susceptible to osmotic lysis. 

Penicillin Binding Protein Pentasaccharide Peptide Mass Fingerprint Peptide YY Peptidoglycans Peptidyl Transferase Center Peptidyl-Dipeptidase PERI... 

A comparison of the structures of penicillin and Dalanyl-Dalanine (cf. structures 41 and 42) shows that there is a great deal of similarity between the two molecules. Penicillin is essentially an acylated cyclic dipeptide of Dcysteine and Dvaline (84). As such, it contains a peptide bond, that of the /3-lactam ring, that can acylate the enzyme. Labeling studies of the peptidoglycan transpeptidase of Bacillus subtilis indicate that radioactive penicillin reacts with a sulfhydryl group of a cysteine residue of the enzyme (86). 

The /3-lactam bond is broken (instead of the equivalent peptide bond joining the alanine residues) but the remaining ring system in the /3-lactam (a thiazolidine in penicillins) is not released (Fig. 8.3). Instead, the transpeptidase remains linked to the hydrolysed antibiotic with a half hfe of 10-15 minutes. Whilst bound to the / -lactam, the transpeptidase cannot participate in further rounds of peptidoglycan... 

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]. 

Figure 2.7. The outer membrane of Gram-negative bacteria. Abbreviations LB, LamB protein LP, lipoprotein O, OmpA protein MP, membrane protein. The peptidoglycan backbone consists of alternating residues of A-acetylglucosamine and /V-acetylmuramic acid, which are cross-linked via short peptides.

It is now well understood that all glycopeptide antibiotics exert antibiotic activity against Gram-positive bacteria because they stereospecifically bind to the precursor peptidoglycan peptide terminus A-acyl-o-alanyl-D-alanine produced during bacterial... 

Friulimicins - antimicrobial peptides that inhibit peptidoglycan synthesis... 

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