Peptidoglycan ppt

Helpful for students of zoology as well as biochemistry...

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2. MAH RUKH ABDUL MAJEED ANIMAL BIOCHEMISTRY PEPTIDOGLYCANS 2

3. Cell wall Envision a cold rainy day. You're sitting in your home, gazing out the window. But, despite the bad weather, you're warm and dry thanks to the roof over your head. Bacteria have something very similar to a 'roof over their head' called a cell wall. The cell wall surrounds the entire bacteria, holding the cell together and offering protection. It also maintains osmotic pressure, meaning it lets in just the right amount of water and ions that the cell needs. 3

4. What is Peptidoglycan? Similar to the roof on our home, the cell wall is rigid to help secure the shape of the bacteria. The cell wall contains a layer of peptidoglycan, a molecule naturally found only in bacteria. The peptidoglycan layer acts as the cell wall's backbone, offering strength to the cell wall. Peptidoglycan, also known as murein , is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall [1]. 4

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6. PEPTIDOGLYCAN The peptidoglycan layer is substantially thicker in gram-positive bacteria (20 to 80 nanometers) than in gram-negative bacteria (7 to 8 nanometers), with the attachment of the S-layer [2][3][4]. Peptidoglycan forms around 90% of the dry weight of gram-positive bacteria but only 10% of gram-negative strains. P resence of high levels of peptidoglycan is the primary determinant of the characterization of bacteria as gram-positive.[5] In gram-positive strains, it is important in attachment roles and serotyping purposes.[6 ] 6

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8. STRUCTURE OF PEPTIDOGLYCAN The peptidoglycan layer in the bacterial cell wall is a crystal lattice structure formed from linear chains of two alternating amino sugars, namely N- acetylglucosamine ( GlcNAc or NAG) and N- acetylmuramic acid ( MurNAc or NAM ). The alternating sugars are connected by a β-(1,4)- glycosidic bond [2][3][4][6]. Each MurNAc is attached to a short (4- to 5-residue) amino acid chain, containing L-alanine, D-glutamic acid, meso-diaminopimelic acid, and D-alanine in the case of Escherichia coli (a Gram-negative bacterium) or L-alanine, D-glutamine, L-lysine, and D-alanine with a 5-glycine interbridge between tetrapeptides in the case of Staphylococcus aureus (a gram-positive bacterium ) [2][3][4][6]. 8

9. STRUCTURE OF PEPTIDOGLYCAN 9

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11. Transpeptidase Cross-linking between amino acids in different linear amino sugar chains occurs with the help of the enzyme DD- transpeptidase and results in a 3-dimensional structure that is strong and rigid. The specific amino acid sequence and molecular structure vary with the bacterial species [8] . 11

12. BIOSYNTHESIS OF PEPTIDOGLYCANS The peptidoglycan monomers are synthesized in the cytosol and are then attached to a membrane carrier bactoprenol . Bactoprenol transports peptidoglycan monomers across the cell membrane where they are inserted into the existing peptidoglycan.[11 ] 12

13. STEPS OF BIOSYNTHESIS In the first step of peptidoglycan synthesis, the glutamine, which is an amino acid, donates an amino group to a sugar, fructose 6-phosphate . This turns fructose 6-phosphate into glucosamine-6-phosphate . In step two , an acetyl group is transferred from acetyl CoA to the amino group on the glucosamine-6-phosphate creating N-acetyl-glucosamine-6-phosphate. [12] In step three of the synthesis process, the N-acetyl-glucosamine-6-phosphate is isomerized, which will change N-acetyl-glucosamine-6-phosphate to N-acetyl-glucosamine-1-phosphate .[12] 13

14. STEPS OF BIOSYNTHESIS In step 4 , the N-acetyl-glucosamine-1-phosphate, which is now a monophosphate, attacks UTP. Uridine triphosphate , which is a pyrimidine nucleotide, has the ability to act as an energy source. In this particular reaction, after the monophosphate has attacked the UTP, an inorganic pyrophosphate is given off and is replaced by the monophosphate, creating UDP-N- acetylglucosamine (2,4) . This initial stage, is used to create the precursor for the NAG in peptidoglycan. In step 5, some of the UDP-N- acetylglucosamine (UDP- GlcNAc ) is converted to UDP- MurNAc (UDP-N- acetylmuramic acid) by the addition of a lactyl group to the glucosamine. Also in this reaction, the C3 hydroxyl group will remove a phosphate from the alpha carbon of phosphenol pyruvate. 14

15. STEPS OF BIOSYNTHESIS In step six , NADPH reduce enol derivative into “ lactyl moiety ”. In step 7 , the UDP– MurNAc is converted to UDP- MurNAc pentapeptide by the addition of five amino acids, usually including the dipeptide D- alanyl -D-alanine .[12] Each of these reactions requires the energy source ATP.[12] This is all referred to as Stage one. 15

16. STEPS OF BIOSYNTHESIS Stage two occurs in the cytoplasmic membrane. It is in the membrane where a lipid carrier called bactoprenol carries peptidoglycan precursors through the cell membrane. Bactoprenol will attack the UDP- MurNAc penta , creating a PP- MurNac penta , which is now a lipid. UDP- GlcNAc is then transported to MurNAc , creating Lipid-PP- MurNAc penta-GlcNAc , a disaccharide, also a precursor to peptidoglycan.[12] 16

17. STEPS OF BIOSYNTHESIS How this molecule is transported through the membrane is still not understood. However, once it is there, it is added to the growing glycan chain.[12] The next reaction is known as Tranglycosylation . In the reaction, the hydroxyl group of the GlcNAc will attach to the MurNAc in the glycan, which will displace the lipid-PP from the glycan chain. The enzyme responsible for this is Transglycosylase .[12] 17

18. BIOSYNTHESIS OF PEPTIDOGLYCANS 18

19. FUNCTIONS OF PEPTIDOGLYCAS There are basically two main functions of peptidoglycans in bacteria: Counter act to maintain the O smotic pressure of cell. When peptidoglycan is absent the bacteria undergo abrupt osmotic lysis . So the most important target of all useful antibiotics is the peptidoglycan. These antibiotics inhibit the synthesis of cell wall of bacteria that results into the osmotic lysis of bacterial cell . 19

20. FUNCTIONS OF PEPTIDOGLYCAS Diffusion of molecules into cells is also regulated by peptidoglycans that play important role in division of cell and anchoring structure for cell wall, teichoic acid. Peptidoglycan fragments are also release by some bacteria that play role in cell to cell communication [12][11]. 20

21. FUNCTIONS OF PEPTIDOGLYCAS A common misconception is that peptidoglycan gives the cell its shape; however, whereas peptidoglycan helps maintain the structural strength of the cell, it is actually the MreB protein that facilitates cell shape.[2][3][4] Peptidoglycan is also involved in binary fission during bacterial cell reproduction. 21

22. References Schleifer , K.H., and Kandler (1972), “Peptidoglycan types of bacterial cell walls and their taxonomic implications”. Bact. Rev., 36, 407. Popp D, Narita A, Maeda K, Fujisawa T, Ghoshdastider U, Iwasa M, Maéda Y, Robinson RC (2010). "Filament structure, organization, and dynamics in MreB sheets".The Journal of Biological Chemistry. 285 (21): 15858–65 Van den Ent F, Amos LA, Löwe J (2001). "Prokaryotic origin of the actin cytoskeleton.". Nature. 413 (6851): 39–44. Van den Ent F, Johnson CM, Persons L, de Boer P, Löwe J (2010). "Bacterial actin MreB assembles in complex with cell shape protein RodZ .". EMBO J. 29 (6): 1081–90. C.Michael Hogan. 2010. Bacteria. Encyclopedia of Earth. eds. Sidney Draggan and C.J.Cleveland , National Council for Science and the Environment, Washington DC. 22

23. Salton MR, Kim KS (1996). Baron S, et al., eds. Structure. In: Baron's Medical Microbiology (4th ed.). Univ of Texas Medical Branch. Demchick PH, Koch AL (1 February 1996). "The permeability of the wall fabric of Escherichia coli and Bacillus subtilis ". Journal of Bacteriology. 178 (3): 768–73. Madigan, M. T., J. M. Martinko , P. V. Dunlap, and D. P. Clark. Brock biology of microorganisms. 12th ed. San Francisco, CA: Pearson/Benjamin Cummings, 2009. Arbeloa A, Hugonnet JE, Sentilhes AC, Josseaume N, Dubost L, Monsempes C, Blanot D, Brouard JP & Arthur M (2004) Synthesis of mosaic peptidoglycan cross-bridges by hybrid peptidoglycan assembly pathways in gram-positive bacteria. J Biol Chem 279: 41546–41556. Atrih A, Bacher G, Korner R, Allmaier G & Foster SJ (1999b) Structural analysis of Bacillus megaterium KM spore peptidoglycan and its dynamics during germination. Microbiology 145: 1033–1041. Doyle R.J., Dziarski R(2001)., in Molecular Medical Microbiology ( Susmsman M., ed.) pp. 137 ‑ 153, Academic Press. White, D. (2007). The physiology and biochemistry of prokaryotes (3rd ed.). NY: Oxford University Press Inc. 23

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