Adherence Flashcards
what must a pathogenic microbe do to survive in a host and establish infection (5)
- attach to host cells for colonization
- evade host’s innate and adaptive immune defenses and persist
- obtain iron and other nutrients needed to multiply
- disseminate or spread within a host and to other hosts
- produce symptoms of disease (to be considered pathogenic)
what is adherence mediated by (2)
- bacterial appendages or surface structures
- interactions can occur directly or indirectly
adherence: direct interactions
- “adhesin” on bacterium binds directly to a specific receptor
adherence: indirect interactions (2)
- adhesin binding first to the protein in the extracellular matrix (ECM)
- then, the ECM proteins binds to specific receptors on the host cell, acting as a bridge
adherence: indirect interactions (2)
- adhesin binding first to the protein in the extracellular matrix (ECM)
- then, the ECM proteins binds to specific receptors on the host cell, acting as a bridge
types of adhesins (2)
- fimbrial adhesins
- afimbrial adhesins
fimbrial adhesins (3)
- fimbriae or pili
- several types that form polymers
- Pap pilus is heavily characterized and studied
afimbrial adhesins (2)
- several types
- a single protein
why do bacteria use long fragile structures to bind to host cells (3)
- outreach
- protection and survivability of core bacterial body from host immune system
- bacterial surface and host cell are negative; allows for connection despite repulsive forces
can bacterium have multiple adhesins
- yes, they can be expressed all at once or sequentially during infection at different stages of pathogenesis
are all adhesins virulence factors (2)
- as bacteria can have multiple adhesins, it is difficult to prove necessity of any one adhesin
- not all adhesins are virulence factors
host receptors for adhesins (4)
- often carbohydrate-based
- glycolipids or glycoproteins
- often integrins
- receptors determine the tropism of the disease
what is the receptor for Pap pilus (3)
- glycolipid
- a P-blood group antigen called gal (alpha1-4) gal
- found in the upper bladder and near the kidney (defining its tropism)
what is the receptor for H. pylori (2)
- Lewis B-blood group antigen
- found in stomach epithelium
tropism
- tissue specificity
what binds to integrins
- ECM proteins or bacterial adhesins that contain RGD motif
integrins (3)
- have 2 chains: alpha and beta chains
- have an extracellular and intracellular domain
- intracellular domain is involved in signaling
what is the RGD motif (2)
- arginine, glycine, aspartic acid sequence
- often binds integrin
integrin example
- CR3
pathogenic E. coli (3)
- causes a variety of diseases
- all pathogenic E. coli express toxins and adhesins
- gram negative
diseases caused by pathogenic E. coli (4)
- gastrointestinal
- invasive
- meningitis
- UTIs
gastrointestinal pathogenic E. coli (2)
- watery diarrhea (cholera-type)
- bloody diarrhea (shigella-type)
invasive pathogenic E. coli
- salmonella-type infection
UTIs (2)
- 5-10% of people have a UTI in their life
- UTIs can be caused by variety of organisms, including E. coli
what are the host defenses in our urinary tract against UTIs (5)
- pH
- microbiota
- flushing
- metabolites
- osmolarity
pyelonephritis (3)
- caused by urinary pathogenic E. coli (UPEC)
- colonization of the gut or vagina serves as reservoir for organism
- bacteria then colonize the bladder and ascend to the kidneys
UPEC virulence factors (3)
- adhesins
- hemolysin (toxin that lyses RBCs and released iron)
- serum resistance proteins
how are UPEC virulence factors connected
- they are linked together on the chromosome; found in a gene cluster
Pap pilus assembly proteins (3)
- structural component proteins
- assembly proteins
- gene regulation proteins
Pap pilus gene regulation proteins (2)
- PapI
- PapB
Pap pilus structural components (6)
- PapA
- PapH
- PapE
- PapF
- PapG
- PapK
Pap pilus assembly proteins (2)
- PapD: chaperone
- PapC: usher
Pilus structure (6)
- PapG: binds to host
- PapF: adaptor protein
- PapE: multi-subunit
- PapK: adaptor
- PapA: multi-subunit
- PapH: interacts with outer membrane
PapG (3)
- the major adhesin
- found on the tip of the pilus as a single protein
- joined to PapE by PapF
PapF
- adaptor between PapG and PapE
PapE
- subunits make up the thin fibrillum
PapK
- adaptor between the thick pilus PapA rod and the PapE fibrillum
PapA
- polymer of repeating PapA subunits makes up a thick pilus rod
PapH (2)
- terminates assembly of the pilus
- links the rode to the outer membrane
Pilus assembly: PapD (2)
- assists in folding of subunits when they enter the periplasm
- properly folded subunits are founds as assembly modules
Pilus assembly: missing PapD (2)
- subunits will misfold and aggregate
- aggregation will lead to degradation
donor strand complementation (3)
- C-terminus of the subunits have alternating hydrophobic residues
- subunits line up in register with a similar region in PapD
- two beta strands (one from subunit and one from chaperone) are found in parallel conformation
Pilus assembly: PapC (3)
- assembly site for the pilus
- where donor strand exchange (DSE) occurs
- directs the ordered assembly of the subunits by influence of relative affinities of subunits and abundance of subunits
donor strand exchange (4)
- at PapC, the PapD chaperone is released, allowing the subunits to polymerize
- one strand from the subunit and one strand from another subunit are now found in anti-parallel conformation
- this new interaction is very strong as it has high affinity
- interaction occurs via the N-terminus of the incoming subunit
donor strand complementation vs exchange (2)
- chaperone/subunit interactions are “loose”
- subunit/subunit interactions are stable and tight; strand snap into place
affinities and order for PapC (3)
- PapD + PapG has highest affinity for PapC, so it binds first
- PapD + PapF assembly module is next, and so on
- PapH finds and anchors the pilus as it lacks the region that initiates DSE
what is a strategy to produce soluble PapG
- genetically link donor strand from chaperone to PapG to prevent PapG from misfolding and degrading
