Biosynthesis of Peptidoglycan.pdf

Biosynthesis of Peptidoglycan

1. BIOSYNTHESIS OF PEPTIDOGLYCAN
(Gram Positive and Gram Negative bacteria: Cell wall)
Presented by
John Avinash. R
BP221517
I M.Sc. Applied Microbiology

2. BACTERIAL CELL WALL

3. The Cell Wall
Gram PositiveGram Negative
•Bacteriamaybeconvenientlydividedintotwofurthergroups,dependingupontheir
abilitytoretainacrystalviolet-iodinedyecomplexwhencellsaretreatedwith
acetoneoralcohol.
•ThisreactionisreferredtoastheGramreaction:namedafterChristianGram,who
developedthestainingprotocolin1884.
Gram Staining

4. DEFINITION OF PEPTIDOGLYCAN
•Peptidoglycan, also called murein, is a polymer that makes up the cell wall of
most bacteria.
•It is made up of sugars and amino acids, and when many molecules of
peptidoglycan joined together, they form an orderly crystal lattice structure.
•Bacteria are classified as being either Gram-positive or Gram-negative based
in differences in the structure of their peptidoglycan cell wall.
•Archaea do not have a cell wall consisting of peptidoglycan, but some do have
a layer of pseudopeptidoglycan (pseudomurein), which is a similar polymer.

5. Bacterial Cell Wall
G +ve
Cell wall
G –ve
Cell wall

6. •Gram positive bacteria and Gram negative bacteria differ in the appearance of cell wall.
•The cell wall of Gram negative bacteria is multilayered structure and quite complex.
•Gram positive bacteria contain primarily single type of molecule and is often much
thicker.
CELL ENVELOPE OF PROKARYOTE:

8. •In the cell wall of bacteria, there is one rigid layer that is
primarily responsible for strength of the wall.
•In Gram negative bacteria additional layer is present
outside this rigid layer.
•The rigid layer of both Gram negative bacteria and Gram
positive bacteria is very similar in chemical composition and
is called Peptidoglycan (or murein).
•This layer is thin sheet composed of two sugar derivatives,
N-acetyl glucosamine and N-acetyl muramic acid (NAM
&NAG) and small number of amino acids consisting of L-
alanine, D-alanine, D-Glutamic acid and either lysine or meso-
diaminopimelic acid
BACTERIAL CELL WALL AND
PEPTIDOGLYCAN COMPONENT:

9. •These constituents are connected to form a repeating structure, glycan
tetrapeptide.
•Basic structure of peptidoglycanis a thin sheetin which the glycan chains
formed by sugars are connected by peptide cross links formed by the amino
acid.
•Glycosidic bonds connecting the sugars in the glycan chains are very strong but
these chains alone cannot provide rigidity in all directions.
•In Gram-negative bacteria cross linkage usually occurs by direct peptide linkage
of the amino group of diaminopimelic acid to the carboxyl group of the terminal
D-alanine.
•In Gram positive bacteria cross linkage is usually by peptide inter bridge. The
kinds and number of cross linking amino acids varies from organism to
organism.
BACTERIAL CELL WALL AND
PEPTIDOGLYCAN COMPONENT:

10. In Gram-negative bacteriacross linkage usually occurs by direct peptide
linkage of the amino group of diaminopimelic acid to the carboxyl group of
the terminal D-alanine.

11. •Peptidoglycan chains connected through short tetrapeptide and pentagiycine bridge.
•The polysaccharide chain consisting of alternate residues of the amino acid N-acetyl
glucosamine (NAG) and N-acetyl muramic acid (NAM) linked in β-1, 4 glycosidic
linkage.
•Each NAM residue carries a short peptide chain of four amino acid residues (tetra
peptide) which are L-alanine, D-Glutamic acid, L-Lysine and D-alanine.

16. •Peptidoglycan is present only in bacteria.
•N Acetyl muramic acidand mesodiaminopimelic acid are never found in the cell walls
of Archae and eukaryote.
•In peptidoglycan, The glycan portion is uniform with only the sugar NAG and NAM
being present, and these sugars are always connected in β1→ 4, linkage.
•Tetra peptide of the repeating unit shows major variation in only one amino acid, the
Lysine, diaminopimelic acid alteration.
•More than 100 different peptidoglycan types are knownand the greater variation
among them occurs in inter-bridge.
•Peptidoglycan constitutes 70-80%of wall in Gram positive bacteria. Lipid content is
little. 10-20%of wall in Gram negative bacteriais formed of peptidoglycan. Lipid
content is 20-30%.
DIVERSITY OF PEPTIDOGLYCON:

17. •Hélène Barreteau, Andreja Kovač, Audrey Boniface, Matej Sova, Stanislav
Gobec, Didier Blanot, Cytoplasmic steps of peptidoglycan biosynthesis,FEMS
Microbiology Reviews, Volume 32, Issue 2, March 2008, Pages 168–
207,https://doi.org/10.1111/j.1574-6976.2008.00104.x
•Stewart-TullDES.1980.The Immunological Activities of Bacterial
Peptidoglycans.Annu. Rev. Microbiol..34(1):311-
340.https://doi.org/10.1146/annurev.mi.34.100180.001523
•Bouhss A, Trunkfield AE, Bugg TD, Mengin-Lecreulx D. The biosynthesis of
peptidoglycan lipid-linked intermediates. FEMS Microbiol Rev. 2008
Mar;32(2):208-33. doi: 10.1111/j.1574-6976.2007.00089.x. Epub 2007 Dec 10.
PMID: 18081839.
REFERENCES