Download Peptidoglycans - Sigma

GLY FINAL 1207 PGD cleanxrefs2
Peptidoglycans
Peptidoglycans
Structure
Bacterial Components
The basic structure of peptidoglycan (PGN) contains a carbohydrate backbone of alternating units of N-acetylglucosamine (GlcNAc) and Nacetylmuramic acid, with the N-acetylmuramic acid residues cross-linked to peptides. Peptidoglycan provides rigidity to the cell wall; the cell walls of
Gram-positive bacteria may contain up to 40 layers of peptidoglycan, conferring significant mechanical strength.1
Structurally, bacteria resemble primitive plants in that the cellular contents are surrounded by an inner peptidoglycan cell wall in addition to an inner
plasma membrane and, in Gram-negative bacteria, an outer lipid bilayer (see Figure 2). In Gram-negative bacteria, peptidoglycans make up about
10% of the cell wall dry weight; while in Gram-positive bacteria the thicker peptidoglycan layer contains about 20% of the cell wall dry weight.
Although the peptidoglycan is responsible for the mechanical strength and shape of bacterial cells, it has sufficient plasticity and dynamic turnover to
allow cell growth and division.
Gram-Positive Bacterial Cell Wall
Gram-Negative Bacterial Cell Wall
Lipoteichoic
Acid
Outer Lipid
Membrane
Peptidoglycan
Cell Wall
Peptidoglycan
Plasma
Membrane
Plasma
Membrane
Alternating copolymer of
b(14)-N-acetyl-D-glucosamine
and N-acetylmuramic acid
Pentaglycine cross-link
L-Ala-D-GluL-Lys-D-Ala
tetrapeptide
Figure 2. The basic structure of bacterial peptidoglycan and the cell wall structures of Gram-positive and Gram-negative bacteria.
Biosynthesis and Degradation
The peptidoglycan biosynthetic pathway begins in the cytoplasm with the synthesis of a muramyl peptapeptide precursor containing a terminal D-AlaD-Ala. L-Alanine is converted to D-alanine by racemase, with subsequent assembly of D-alanyl-D-alanine by D-Ala-D-Ala ligase. In the cytoplasm, the
muramyl pentapeptide precursor is anchored via a water-soluble UDP-glucosamine moiety. In the second phase of peptidoglycan construction, the
muramyl pentapeptide N-acetylglucosamine is transferred to a C55 undecaprenyl phosphate with the release of UMP to form a Lipid I intermediate. An
additional glycosylation step completes the peptidoglycan unit, which is then transported via its C55 lipid tail to the external periplasmic surface of the
membrane, where the peptidyglycan unit becomes integrated into the cell wall matrix. Several transpeptidases and transglycosylases connect the
newly formed peptidoglycan structures to the cell wall peptidoglycan matrix.
Inhibitors of peptidoglycan biosynthesis act as antibiotics in that they lead sequentially to the loss of peptidoglycan, loss of cell wall integrity, and lysis.
Peptidoglycan degradation is catalyzed by glycosidases, peptidases, and amidases, including lysing enzymes such as lysozyme, that are commonly
used for degrading cell walls.
Specific antibacterial compounds that contain a β-lactam structure, such as penicillin, interfere with the synthesis of the cell wall, weakening the
peptidoglycan scaffold within the bacterial wall so the structural integrity eventually fails. Since mammalian cells have a plasma membrane but lack
the peptidoglycan wall structure, this class of antibacterials selectively targets bacteria with no significant negative effect on the cells of the
mammalian host. The specificity of β-lactam antibacterials is due to their structural similarity to the D-alanyl-D-alanine group, allowing them to
compete for the binding sites of transpeptidases and prevent the assembly of peptidoglycan layers in both Gram-positive and Gram-negative bacteria.
30
sigma.com/glycobiology
For Technical Service, call your local office or visit sigma.com/techinfo
GLY FINAL 1207 PGD cleanxrefs2
Peptidoglycans
Functions
References:
1. Stewart-Tull, D.E.S., Major component of the cell wall in Gram positive organisms.
Consists of a glycan backbone with alternating β(1,4) linked residues of N-acetyl-Dglucosamine and muramic acid. The immunological activities of bacterial peptidoglycans.
Ann. Rev. Microbiol., 34, 311 (1980).
2. Schleifer, K.H., and Kandler, O., Peptidoglycan types of bacterial cell walls and their
taxonomic implications. Bact. Rev., 36, 407 (1972).
3. Wheat, L.J., et al.,Antibody response to peptidoglycan during staphylococcal
infections. J. Inf. Dis., 147, 16 (1983).
4. Doyle R.J., Dziarski R., in Molecular Medical Microbiology (Susmsman M., ed.) pp.
137‑153, Academic Press (2001).
5. Alexopoulou, L., et al., Recognition of double-stranded RNA and activation of NF-κB by
Toll-like receptor 3. Nature, 413, 732 (2001).
6. Zhou, R., et al., Substrate for the determination of lysostaphin activity. Anal. Biochem.,
171, 141 (1988).
The Antibiotic Explorer
The Antibiotic Explorer connects you to products for your
specific applications, including:
Cell Culture
Gene Regulation and Expression
Studies
■ Analytical Reference Standards
Plasmid Selection
Plant Tissue Culture
■ Research Antibiotics
■
■
■
■
Bacterial Components
The primary immune recognition is based on structures common among
invading pathogens. Surface molecules, such as lipopolysaccharide (LPS),
peptidoglycans, and peptidoglycan recognition protein (PGRP), are
known to elicit immune reactions ranging from cytokine release to
fever.2‑4 Peptidoglycans activate the Toll-like receptor 2 (TLR2), that is
present in mammalian cells, and they can be used for the stimulation of
lymphocytes. Peptidoglycans also function as antagonists of Poly(I:C).5
Peptidoglycans may be used to estimate the activity of lysing enzymes
such as lyticase.6
Peptidoglycans
Name
Cat. No.
Peptidoglycan from Bacillus subtilis
69554-10MG-F
Peptidoglycan from Methanobacterium sp.
78721-10MG-F
Peptidoglycan from Micrococcus luteus
53243-10MG-F
Peptidoglycan from Saccharomyces cerevisiae
72789-10MG-F
Peptidoglycan from Staphylococcus aureus
77140-10MG
77140-25MG
Peptidoglycan from Staphylococcus staphylolyticus
08678-10MG-F
Peptidoglycan from Streptomyces sp.
79682-10MG-F
To access the largest selection of research antibiotics, visit
sigma-aldrich.com/antibiotic
sigma-aldrich.com
Your Favorite Gene™, Your Comprehensive Gene Search Tool, visit sigma.com/yfg
31