1 / 13

Assembly of peptidoglycan

Assembly of peptidoglycan. Lengeler et al. Chapter 23 pp. 555-570 Assembly of cell structures 1. Functions of peptidoglycan 2. Peptidoglycan monomer 3. Three stages: enzymatic assembly 4. Similarity: penicillin versus D-Ala-D-Ala. Gram-negative cell envelope.

tolla
Download Presentation

Assembly of peptidoglycan

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Assembly of peptidoglycan • Lengeler et al. • Chapter 23 pp. 555-570 • Assembly of cell structures • 1. Functions of peptidoglycan • 2. Peptidoglycan monomer • 3. Three stages: enzymatic assembly • 4. Similarity: penicillin versus D-Ala-D-Ala

  2. Gram-negative cell envelope

  3. 1. Functions of peptidoglycan • Structural integrity: sacculus • Cell shape • Cell division G+ and G- bacteria

  4. 2. Peptidoglycan monomer • 2 sugars: N-acetyl glucosamine (NAG) N-acetyl muramic acid (NAM) • Linkage = β 1  4 • NAG: unsubstituted • NAM: linked to 5 amino acids (aa) L-Ala, D-Glu, L-Lys (or DAP), D-Ala, D-Ala

  5. 3. 1st stage of assembly • 9 enzymatic reactions: cytoplasm • UDP-NAG --PEP + NADPH  UDP-NAM • Addition of each aa to UDP-NAM energy requiring rxns • L-Ala + ATP  UDP-NAM-L-Ala • D-Glu + ATP  UDP-NAM-L-Ala-D-Glu • DAP + ATP  UDP-NAM-L-Ala-D-Glu-DAP

  6. Peptidoglycan monomer • L-Ala –racemase D-Ala • D-Ala + D-Ala + ATP  D-Ala-D-Ala • D-Ala-D-Ala synthetase • both rxns inhibited by cycloserine • UDP-NAM-L-Ala-D-Glu-DAP + D-Ala-D-Ala  • UDP-NAM-L-Ala1-D-Glu2-DAP3-D-Ala4-D-Ala5

  7. 2nd stage of assembly • Transfer reactions: cytoplasmic membrane • C55 polyisoprenyl lipid~PP • synonym = bactoprenyl~P • Links to • UDP-NAM-L-Ala1-D-Glu2-DAP3-D-Ala4-D-Ala5 • NAM--(pentapeptide)-P-P-lipid

  8. Translocation across CM • -NAM—(pentapeptide)-P-P-lipid • + UDP-NAG •  NAG—NAM—(pentapeptide)-P-P-lipid • Inhibited by vancomycin, tunicamycin • Recycling of lipid • Inhibited by bacitracin • Adding monomers to pre-existing peptidoglycan **

  9. 3rd stage of assembly • a. chain formation • Adding more [NAG-NAM-pentapeptide] to existing urein sacculus • Transglycosylase: • NAG-NAM-NAG-NAM-P-P-lipid  • NAG-NAM-NAG-NAM-NAG-NAM-P-P-lipid • Each NAM is substituted with pentapeptide •  Uncrosslinked peptidoglycan

  10. 3rd stage of assembly • a. chain formation, cont’d • Uncrosslinked peptidoglycan  • Transpeptidase: • Cross linking of ε-NH2 group of DAP3 to…. • D-Ala4 on neighbouring strands •  cross linked peptidoglycan

  11. Bifunctional enzyme • Transglycosylase + Transpeptidase • = penicillin binding protein 1a [or 1b] • PBP 1a [or PBP1b] • Anchored in cytoplasmic membrane, facing periplasm

  12. 3rd stage of assembly • b. Maturation of peptidoglycan • Carboxypeptidase • Cleavage of D-Ala5 from cross linked peptidoglycan • -NAG-NAM-NAG-NAM-NAG-NAM-NAG- with each NAM substituted by tetrapeptide • PBP5, PBP6

  13. 4. Structural similarities • Penicillin versus D-Ala-D-Ala • Single target hypothesis • Inhibition of cross linking of peptidoglycan =transpeptidase • Multiple targets of penicillin action = PBPs

More Related