Exam #2

Question 1

General secretory pathway

Answer 1

Features:
-Pore thru: proteins are secreted-trimeric
-11 proteins involved
-signal peptide on protein - 50 to 30 aa in length
-many bacterial proteins secreted by this mechanism

Location:
-cytoplasmic membrane-pore proteins embedded
-Gram+ v. Gram-

Action:
-protein weave through hydrophobic membrane
1. Protein guided to site on membrane-chaperones/usher
2. Protein chain crossed lipid bilayer
3. Translocated protein is released )Signal peptide cleaved)

Question 2

Type 1 secretion pathway

Answer 2

Features:
-Sec-independent
-Composed of 3 proteins
-Specific for certain secreted proteins

Location:
-spans both inner and outer membrane
-only in Gram-

Action
-secretes directly outside, bypasses periplasmic space
-Alpha hemolysin

Question 3

Type II secretion: 2 Step Process

Answer 3

Features:
-sec dependent
-12 to 14 proteins
-similar to type IV pili

Location:
-OMPs secretins
-most components in the cytoplasmic membrane
-some form pili-like strucutres-gude folded protein to other components
-Gram-

ACtion:
-secretins from pores in OM
-other components act as chaperones

Xcp for P. aeruginosa for export of exotoxin A

Question 4

Type III secretion systems: Contact dependent

Answer 4

Features:
-Independent
-More than 20 proteins
-Components similar to those of flagellar apparatus

Location:
-Components form a channel that spans both IM and OM
-Two components fuse with eukaryotic membrane
-Form a injection pore
-Gram- only

Action:
-Inject protein from bacterial cytoplasm to inside of host cell
-secretion triggered by low Ca 2+ cone
-sepcific for certain secreted proteins

Question 5

Type IV secretion system: Conjugal transfer system

Answer 5

Feature:
-sec independent
-large number of proteins

Location:
-pilus like structures occurs in periplasm and transits both membranes
-Gen-

Action:
-transfer monomeric proteins, multimeric proteins and SS DNA with proteins
-proteins injected directly into host cells
-sometimes secreted outside

Examples:
-L. penumophila Dot/IcM
-B. pertussis toxin export system

Question 6

Modulating Host Cytosekeleton

Answer 6

Viruses and bacterial systems

manipulation of host cfell structure by modulation

Cytoskeletal modifications facilitate uptake through non phagocytic cells

Internalized bacteria modulate cytoskeleton for movement

toxins to alter cytoskeleton

Question 7

Modulating of Host Cytoskeleton - Indirect action

Answer 7

-Eukaryotic cytoskeleton maintain cell shape

-Rho family of low-molecular weight GTPases

-Proteins undergo conformational changes in regions called switch I and switch II depending on bound nucleotide

-GTP binding signal on state: membrane ruffling, fliopodia growth or stress fiber formation

-If GTP is hydrolyzed to GDP-GTPase is unable to bind to signal the off state

-Several pathogens encode for factors that modulate Rho-type GTPAses

-Covalent and non-covalent modifications

-Eukaryotic cells regulate reversible binding of GTP/GDP

Question 8

Porins

Answer 8

Protein channels located in outer membrane of G- to allow for passive diffusion of small molecules including nutrients and certain antibiotics

Resistant Mechanism:
-reduced porin expression: bacteria can down regulate production decreasing the number of channels available for antibioitcs
-Porin modification: mutations in porins can alter their size or change, restricting entry of antibiotics

Impact on antibiotic resistance:
-reduced uptake of antibiotics particulary hydrophilic like B-lactams
-slower accumulation of drugs within the bacterial cell

Question 9

Efflux pumps

Answer 9

Transport proteins that actively expel toxic substances out of bacterial cell

Resistant mechanism:
-overexpression can increase the number of pumps leading to efficient expulsion of antibiotics
-Broaad substrate specificity: remove a wide range of antibioitcs making them highly versatile

Impact:
-decreased intracellular concentration of antibioitcs to prevent them from reaching targets in effective dose
-Resistance to a variety of antibiotic classes

Question 10

Mechanism of Antibiotic Resistance

Answer 10

4 categories

1. Restricted access of AB to target
   -porins
   -efflux pumps
2. Enzyme inactivate by hydrolizing or adding chemical groups
3. Modification of AB target
   -change in rRNA critical for binding
   -change target protein - no longer binds AB
4. Failure to activate
   -metronidazole: activated before it can work on DNA
   -resistance mediated by housekeeping genes
   -multiple mechanismx work at the same time