1 / 34

Unicellular Organisms: Eubacteria, Archea, Yeast Lecture 27, Chapter 21 May 13, 2004 Jeff Esko

Unicellular Organisms: Eubacteria, Archea, Yeast Lecture 27, Chapter 21 May 13, 2004 Jeff Esko. Overview. General structure of bacterial cell walls Structure, function and assembly of peptidoglycan (murein) Periplasmic  -glucans (MDO) Lipopolysaccharide (LPS) - endotoxin

perrin
Download Presentation

Unicellular Organisms: Eubacteria, Archea, Yeast Lecture 27, Chapter 21 May 13, 2004 Jeff Esko

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. Unicellular Organisms: Eubacteria, Archea, Yeast Lecture 27, Chapter 21May 13, 2004Jeff Esko

  2. Overview • General structure of bacterial cell walls • Structure, function and assembly of peptidoglycan (murein) • Periplasmic -glucans (MDO) • Lipopolysaccharide (LPS) - endotoxin • Capsular polysaccharides - mimicry • Archea glycoproteins - a new area • Yeast glycosylation and cell walls

  3. Capsule LPS PG MDO Gram-negative bacteria cell wall

  4. A A A A D D D D G G G G A A A A A A A A G G G G D D D D A A A A A A A D D D G G G A A A A A A A G G G G D D D D A A A A A A A A D D D D G G G G A A A A A A A A G G G G D D D D A A A A Peptidoglycan [GlcNAcb1,4MurNAcb1,4]n Heijenoort (2001) Glycobiology 11:25R

  5. C H O H C H O H 2 2 O O O O O O O H C C H N H A c N H A c 3 O C L - A l a D - G l u D A P D - A l a D - A l a Murein Glycopeptide Notice D-amino acids DAP = diaminopimelic acid

  6. A A A A D D D D G G G G A A A A A A A A G G G G D D D D A A A A A A A D D D A A A A G G G A A A A A A A G G G G D D D D A A A A A A A A D D D D G G G G A A A A A A A A G G G G D D D D A A A A Peptidoglycan The final step involves cleavage between the D-Ala-D-Ala unit and transpeptidation to the amino group of DAP of another unit

  7. Vancomycin

  8. Moenomycins

  9. P Peptidoglycan Biosynthesis Undecaprenyl phosphate

  10. MDO Gram-negative bacteria cell wall

  11. b2 b2 b2 b2 b2 b2 b2 Membrane Derived Oligosaccharides (MDO) • Branched -glucans • Represent about 1-5% of dry weight • Charged substituents act as an osmolyte and protects the inner membrane against the large difference in osmolarity inside the cell compared to outside the cell + Phosphoethanolamine + Phosphoglycerol + Succinate

  12. LPS Gram-negative bacteria cell wall

  13. Lipopolysaccharide (LPS) • LPS consists of three domains • Lipid A, otherwise known as endotoxin • Core region composed of KDO (K), heptoses (H), and hexoses (open hexagons) • Highly variable outer O-antigen region

  14. H O O H H O H O H O U r i d i n e U r i d i n e N H AcN O H O H O H O H H O H O O O O O O O O P P P P O O O C O O O O O • Initiates by acylation of UDP-GlcNAc at C3, followed by N-deacetylation, and N-acylation Wyckoff et al. (1998) Trends Microbiol. 6:154

  15. O H O H O H C H 2 O O O O H O O O H O H O O O O O O H O O U r i d i n e N H P P N H N H O P O C O O O C O O C O O N H P O O H O H O O O C O O H O O O H H O H O H O H O H O H O H O H O Lipid A Assembly + Diacylglucosamine-1-P condenses with another molecule of UDP-diacylglucosamine to form the tetraacyl disaccharide core

  16. Lipid A Assembly • KDO transferases initiate the formation of the core • Additional C12 fatty acids added to -hydroxy groups (wax) • Lipid A translocates to the outer leaflet of the outer membrane by msbA (ABC transporter) Doerrler et al. (2001) J Biol Chem. 276:11461

  17. Lipid A Biology • Lipid A, the heat stable endotoxin of gram negatives • Resistant strains of mice defined a locus, lps, which was positionally cloned. • lps turned out to be homologous to toll receptors in Drosophila, which were known to be involved in innate immunity to fungal infection • lps turns out to beTlr4, a member of a family of signaling receptors (10 members known). • Tlr4 binds to Lipid A. • Tlr2 apparently binds and responds to muramyl-dipeptide

  18. Takeda & Akira (2001)Genes to Cells 6:733

  19. LPS Structural and Functional Domains

  20. C H O H 2 C H O H 2 H O H C C H O H O C O O H O H O O H O H O H O H O H O H Core region contains unusual sugars • The inner core contains 1-4 KDO residues, which look like an analog of sialic acid. • The core also contains heptopyranoses, which can vary stereochemically • The rest of the core consists of various combinations of Glc and Gal 3-deoxy-D-manno-octulosonic acid (KDO) L-glycero-D-manno- heptulose

  21. LPS Structural and Functional Domains

  22. O-antigen Structure O9 a 3 a 2 a 2 a 2 a 3 O6 a 3 b 4 b 3 a 4 b 2 O124 b 3 b 6 a 3 a 4 G l c L A b 6 GlcLA = glucolactillic acid O-antigens • O-antigens consist of 2-8 sugars, repeated ≤50 times • O-antigens gives rise to different serotypes and some are correlated with disease

  23. Capsule Gram-negative bacteria cell wall

  24. a4 b4 a4 b4 a4 a8 a8 a8 a8 a8 b4 b3 b4 b3 b4 Capsule type Structure K1, polysialic acid K5, N-acetylheparosan Group A Streptococcus (hyaluronan) • Mucoid strains contain a polysaccharide capsule • >80 different capsules types are known just in E. coli • Extraordinary diversity of structure

  25. Mycobacteria Crick et al. (2001) Glycobiology 11:107R

  26. Crick et al. (2001) Glycobiology 11:107R

  27. Crick et al. (2001) Glycobiology 11:107R

  28. Bacterial Glycoproteins • Surface-layer (S-layer) glycoproteins • Prevalent in Bacteria and Archaea, but structures differ, e.g., N-linked glycosylation only in Archaea • Structural analyses have revealed unusual carbohydrate-linkage regions…. • ….and unusual nucleoside diphosphate-linked oligosaccharides

  29. Schaffer et al (2001) Proteomics 1:248

  30. Notice diversity of linkages Similarity in sequence of N-linked attachment sites and mechanism of assembly of glycan (dolichol pathway) Burda & Aebi (1999) Biochim Biophys Acta 1426:239

  31. Yeast make AsN-linked Glycoproteins • Yeast make membrane N-linked glycoproteins much in the same way as higher eukaryotes • Serves as a model for human genetic diseases (CDG) M Aebi (2001) Trends in Cell Biology 11:136

  32. a 6 a 6 a 2 a 3 a 2 a 6 a 2 a 3 a 2 a 6 a 2 a 3 a 2 a 3 a 6 a 2 a 3 a 2 a 3 a 3 a 2 a 6 a 6 a 3 -1-P a 2 a 4 a 3 a 6 a 6 -P- a 2 a 3 a 2 a 2 a 3 a 6 a 2 a b4 a Ser/Thr Ser/Thr b4 Vertebrate a-dystroglycan Asn Yeast Mannans Willer et al (2003) Curr Opin Struct Biol 13:621

  33. GPI proteins GPI proteins GPI proteins Pir cell wall proteins b1,6-glucans b1,6-glucans b1,6-glucans b1,3-glucans Plasma membrane Yeast Cell Walls The cell wall is made of 60% b-glucans, 40% mannoproteins, and ~1% chitin Smits et al (2001) Microbiology 147:781

  34. Summary • Bacterial cell walls are complex layered structures composed of multiple classes of glycans • Bacterial wall glycans provide an exoskeleton, define shape, protect against turgor pressure, create antigenic serotypes, and provide a way to prevent immune recognition • Glycosylated proteins are present in eubacteria and in archaea • Yeast produce many of the same glycans found in higher eukaryotes, but the mecahnism of assembly differs in subtle way • Yeast cell walls are composed of glycans (glucans and chitin) • Yeast and bacteria provide powerful genetic systems for understanding membrane and cell wall assembly

More Related