5 - Lipopolysaccharide, periplasm and flagella Flashcards
1
Q
Lipopolysaccharide info (LPS)
A
- Large complex molecules containing lipid and carbohydrate
Used in: - lipid A
- core polysaccharide
- O side chain
- called endotoxin when free in host (consequence of being in bloodstream)
- can induce massive immune response (septic shock)
- not a function of LPS but an effect of its interaction with innate immune system
2
Q
LPS structure - simple
A
Made of:
- lipid A
- Core polysaccharide
- O specific polysaccharide/O specific side chain
3
Q
Lipid A info
A
- two glucosamine residues linked to fatty acids and phosphate (occasionally more than one phosphate - e.g. pyrophosphate)
- integrated into the outer membrane
- component most immunogenic as endotoxin
- remaining LPS projects from cell surface from Lipid A
4
Q
Core polysaccharide in LPS info
A
- referred to also as R-antigen or R-polysaccharide
- made of 10 (mostly) unusual sugar residues (in Salmonella) - very specific to organism
- such as glucose, galactose, heptulose, etc.
- Core polysaccharide has side chains of NAG (used in peptidoglycan), phosphate and ethanolamine
5
Q
O side chain info
A
- Is a variable region - responsible for antigenic makeup of bacteria
- so this is part of LPS that interacts with other cells, involved in cell communication
- different O serotypes linked to diseases
- species specific attachment to specific receptors
- extends outwards from the cell
- lipid A and core polysaccharide are straight and O side chain is flexible and bent - easier to bind to specific binding sites and regions
- highly variable composition (at least 20 different sugars)
- rough (R)/Smooth(S) variants depend on O-specifc side chain length
6
Q
Function of LPS
A
- lipid A stabilises outer membrane structure
- core polysaccharide charged - contributes to negative charge on surface
- charged, hydrophilic external layer
- reduces permeability of hydrophobic substances
- e.g. prevent entry of bile salts, antibiotics used to kill bacteria
- protects against host defences
- rough LPS variants more susceptible to phagocytosis
- loss of O-antigen in E. Coli and other bacteria leads to reduced virulence
- O-antigen/side chain very variable, helps identify certain bacteria in diagnosis and medicine etc.
7
Q
Endotoxin release from bacteria
A
- many pathogens produce endotoxins
- released during cell division or by lysis of bacterial cells
- can act to prime immune system against a pathogen
- if in blood, LPS can cause septic shock syndrome
- no direct treatment
- endotoxins immunogenic even in absence of living cells
- LPS of some non-pathogens can also be endotoxin
- test for endotoxin:
- rabbit pyrogen test - old
- now use LAL essay
8
Q
Old and new method of testing for endotoxins in blood if infected by bacteria
A
Old: rabbit pyrogen test - ethics
New: LAL essay
9
Q
Important properties of endotoxins
A
- heat stable
- toxic in nano gram amounts (very small amounts)
- interacts with innate immune system cells
- this can trigger release of cytokines in a cascade
- actives transcription factors and other immune responses etc,
Can result in varying symptoms after infections and disease, inflammation, fever, etc.
10
Q
Why don’t phages mutate to become more efficient
A
Mutations make cells more susceptibile to phage infection, as they are sites in which
phages can pump DNA into the cell
11
Q
Outer membrane as a permeability barrier
A
- outer membrane more permeability - due to presence of porins
- porins are protein channels that permit passage of small molecules up to around 600 Da (molecular weight units)
- larger molecules can also cross OM (outer memebrane) , via AT, through AT systems but not through porins
12
Q
Porin super family info
A
- homotrimeric (three identical units of polypeptide), transmembrane proteins
- highly conserved structure
- as have similar amino acids involved in binding and transfer of molecules across the membrane
- form water filled channels in OM
13
Q
Porin selectivity
A
- most are non-specific channels that allow passage of small (<600 Da) hydrophilic molecules
- most porins are slighlty cation selective
- some porins are selective, etc.
- substances that attack bacteria exploit the porins in outer membrane and their selectivity
14
Q
Periplasmic space info
A
- compounds diffuse through porins into periplasm
- periplasm is the space between outer membrane and cytoplasmic membrane
- ranges in size from 1-70nm
- can be up to 40% of cell volume
- gel-like consistency due to abundant proteins
- removal of cell walls without lysing the cells allows study of proteons and ezymes present in this space
15
Q
Enzyme activity in periplasm examples/info
A
- nutrient acquisition - hydrolytic enzymes
- energy conservation - ETP proteins
- some peptidoglycan can synthesise enzyme in periplasm
- periplasmic binding proteins - ABC transporters - deliver specific compounds to ABC transporters in cytoplasmic membrane
- chemoreceptors - involved in chemotaxis
21
Q
cross-section of porin monomer info
A
- hourglass shape with a central constriction - varies from different porins
- size of molecule that can fit through porin depends on size of that constriction
- hydrophobic band of 25 A that sits in membrane
