Lecture 2 Flashcards
What is one of the most important need in bacterial pathogenesis?
-the need to secrete proteins across one or more phospholipid membranes (inside and outside transport)
what are the roles of secreted proteins across one or more phospholipid membranes
-attachment to host cells, scavenging metabolites, direct toxic activity and disrupting host cell functions
where are these protein secretion systems used by bacteria as virulence factors
-from the cytosol of the bacteria into host cells or host environment
true or false: protein secretion systems to secrete virulence factors are not divided
false they can be divided into distinct classes, based on their structure, function and specificity
true or false; all secretion systems are conserved across all bacterial species
false some are only scpecies specific
true or false: gram positive secretion systems are more complicated
false; it’s the gram - ones that are more complicated due to the two membranes
what are the gram + secretion systems
-general sec pathway
-twin arginine translocation (TAT)
-sortase
-T4SS
-T7SS (including mycobacteria)
what are the gram - secretion pathways
-general sec pathway
-TAT
-T1SS-T6SS
-T8SS-T9SS
-outer membrane vesicles
which secretion pathways are the most commonly used systems to transport proteins across the cytoplasmic membrane
-the general secretion (sec) and the twin arginine translocation (TAT)
true or false: most proteins transported by the sec and the tat pathways remain inside the cytoplasm
wrong it is in the periplasm or the inner membrane
true or false: gram - bacteria can use more than 1 secretion pathway
true
-proteins delivered to the cytoplasmic membrane or periplasm can stay in those compartments or be transported outside of the cell via another secretion system
what is the sec pathway for
-transport unfolded proteins that have an n terminal signal sequence
the sec machinery is essential for…..
bacterial viabilitu
what does the sec machinery consist of
-peripheral membrane atpase SecA
-channel composed of SecE, SecG and SecY
translocation in the sec pathways is powered by….
-secA catalyzed atp hydrolysis as well as the proton motive force
the signal sequence in the sec pathways is cleaved by the ….
signal peptidase (SP)
e.coli uses the sec pathwatys for … of its secretome
96%
what is the TAT secretion pathway? for ?
-it is for transporting fully folded proteins
true or false: the TAT pathway is present in all the bacteria
false it is not
proteins are targeted to the TAT machinery by…….
signal peptided with a conserved twin arginine containing motif
many exported proteins containing non-covalently bound factors (heme, metals) are secreted through….
the TAT system
the TAT system is energyzed by…
the proton motive force
several oathogens including pseudomonas aeruginosa, yersinia pseudotuberculosis and e.coli require …. for full virulence in animal infection models
a functional tat pathway
examples of p aeruginosa virulence factors that require TAT first then T2SS
-phospholipase c : hemolytic
-toxA- exotoxin A
what do sortases do
-sortase anchors proteins to the cell wall of gram + bacteria
following secretion through the sec pathway, sortase (SrtA) recognizes what
LPxTG motif present at the C terminus of some proteins
what do sortases cleave
-cleaves the protein between the thr and the gly residues and forms an amide bond between the c terminal thr and gly present on the lipid II peptidoglycan precursor
give examples of bacteria that uses sortase
-s aureus protein A (Ig binding), pilins, adhesins and enzymes
what does SpA do
limits opsonization mediated phagocytosis and antibody production
T7SS are also known as … systems
ESX
where is the T7SS found
-mycobacteria
-actinobacteria
-firmicutes like s aureus, l monocytogenes and b subtilus
what is the role of the T7SS secretion system
-exports small proteins of 100 amino acids that have a conserved WXG motif which adopt a helix turn helix structure
the exported proteins that went through the T7SS form…
homo or hetero dimers
give examples of proteins from tuberculosis that went through T7SS
esat 6 and cfp-10
how many esx systems does m tuberculosis has
5 and 3 of which are required for fu;; virulence
t7ss contains several core inner membrane proteins, what are their names and what do they intereact with
-EccB-E that interact with sytosolic chaperones aka EspG to form a pore through which proteins are secreted
what is Myc-P important for
-mycosin is an essential substilisin like serine proteases that stabilizes the membrane complex
what does esx-1 do
-secretes the esxa-esxb heterodimer (esat6/cfp10)
what is esx-1 critical for ?
critical for bacteria survival in the phagosome (absent from BCG vaccine)
ehat does esx 3 do
-involved in mycobactin mediated iron acquisition
what is the role of esx 5
secretes members of the mycobacteria specific PE (pro-glu) & PPE (pro pro glu) protein families
-these may play a role in host immune evasion, nutrient uptale, capsule integrity
what is the name of the unusual cell wall in m tuberculosus
mycomembrane or mAGP
what does imb bz do
it is an inhibitor targeting esx 1
-inhibits the secretion of cfp 10
t7ss may contribute to….
colon cancers
some t7ss substrates produced by bacillus, staphylococcus, streptococcus function as ….
antibacterial toxins
true or false; some secreted proteins by gram - bacteria must cross…
2-3 phospholipid membranes to reach their final destination
true or false: all bacteria have secreted protein pathways that are either TAT or sec
false some move to the IM or OM indepedently from it
true or false: t3ss, t4ss and t6ss can transport proteins directly to the cytosol of a target or host cell
true
t1ss have three essential components
-an abc (atp binding casette) transporter protein in the inner membrane
-a membrane fusion protein that crosses the inner membrane and bridges it to the outer membrane
-the outer membrane factor (OMF)
t1ss often use the multipurpose pore forming protein …
(TolC) as their omf
- TolC is shared with the multidrug efflux system of E. coli known as….
the AcrA/AcrB/TolC system
true or false: t1ss are found in all gram- bacteria
false it is found in most
true or false; t1ss is a one step process accross both the IM and the OM
true
what are the substrates in the t1ss
Substrates range from
-digestive enzymes (proteases, lipases), adhesins
-hemebinding proteins, and pore-forming toxins with “repeats-in-toxins” (RTX) motifs (glycine
- aspartate-rich repeats at the C-terminus of toxin protein
what is one of the best studied t1ss
-HlyA hemolysin of UPEC
what does the HlyA hemolysin do
-the toxin inserts into the membranbes of host cells causing them to rupture (aids in crossing mucosal barriers and in damaging effector immune cells)
what do exotoxins do
they act remotely on the target cells ex: hemolysin, diptheria toxin and tetanus toxin)
what are effector proteins
they are proteins that are injected into the host cell cytoplasm
effector protein secretion is achieved by …
the t3ss and t4ss and t6ss
true or falsel effector protein secretion is sec pathway dependant
false it is independant
t3ss are referred as….
injectisomes or needle ans syringe like apparatus because of their structure
pathogens may secrete few effector proteins like… or several dozen ex… via t3ss
Pathogens may secrete only a few effector proteins (eg. Pseudomonas &
Yersinia), or several dozen (eg. Shigella and enterohemorrhagic E. coli) via T3SSs
the structural components of t3ss are typically encoded on….
pathogenicity islasnds in the bacterial chromosome or on plasmids
true or false t3ss are vertically aquired
false they are horizontally aquired
evolutionarily distinct bacteria may have closely related t3ss
what are the 3 main components of t3ss
-base complex or basal body
-needle component
-translocon
in the t3ss; effector proteins remain unfolded in the…. and bind to…..
effector proteins remain unfolded in the bacterial cytoplasm and bind to specific chaperones to prevent aggregation
where are the proteins secreted from in t3ss
through the needle as unfolded proteins
-effector proteins then fold within the host cell cytoplasm
true or false; effector proteins from t3ss have the capacity to modulate gene expression in its host cells
-false they have the capacity to mpdulate normal cellular functions (host cytoskeleton and host cell signalling pathways)
why do effector proteins from t3ss have the capacity to modulate normal cellular functions
to promote bacterial survival, avoid host immune actication and establish infection
translocationof t3ss effectors is essential for virulence of many pathogens like:…..
-yersinia
-salmonella
-shigella
-chlamydia
what is the t3ss structire
a series of ring structures surrounding a hollow tube
the basal structure is related to the…..
flagelalr basal body
true or false: t3ss evolved from flagella and both contain an atpase complex
true
what does the translocon do
it creates a pore in the host cell membrane for delivery of effector proteins
what does the tip complex do
it senses contact with the host cells
-it is also necessary for insertion of the translocon into host cell membranes
how do translocons assemble
they assemble upon contact with host cells and form a pore that allows for effector delivery
what is the translocon essential for
passage of effectors through host cell membranes
t3ss may sense the host cell through……
mechanical contact or through chemical variations between the extracellular environment and the intracellular host environment ex: ph or ca2+ concentration
how many proteins is t3ss made up of
20
t3ss assembly: what does it require
-early events are sec dependant and require a pgn cleaving enzyme
-later assembly events depend upon the t3ss itself
yersinia t3ss effectors: they have eukaryotic like signalling domains and…
modulate host signaling pathways
true or false: yersinia is considered an extracellular pathogen
true
what is the main role of the t3ss in yersinia
inhibits host cytoskeleton dynamics and contributes to anti phagocytic activity
what does yoph do
POWERFUL TYROSINE PHOSPHATASE (YERSINIA OUTER PROTEIN)
what is yopo
-is a kinase with homology to eukaryotic ser/thr kinases that is activated by binding to actin, rhoa and rac1
secretion systems as targets for therapy
-represents an anti virulence or infective strategy
-potentially a good alternative to traditional antibiotics
what happens if salmonella enterica has a non functional
it is avirulent
true or false: t6ss is the oldesr secretion system to be discovered
false it is the most recent
what do t6ss do
-translocate proteins into a variety of cell types, includieng eukaryotic cells, and more commonly into other bacteria
-also able to transport effector proteins from one bacterium to another in a contact dependent manner
what is the % of gram - genoimes contain genes for t6ss componentys
25%
how many t6ss does yersinia pestis has
6
true or false: t6ss sjare structural homology to phage tails
true
believed to have evolved from inverted phage tails that eject proteins outisde of the bacterial cell rather than injecting them inside
many t6ss effectors are directed against….
the bacterial cell wall and membrabe which supports a role for this apparatus in interspecies bacterial competition
T6SS are structurally &
mechanistically similar to
T6SS are structurally &
mechanistically similar to the
contractile tail of bacteriophage
which is used to inject phage
DNA into target bacterial cells
VipA/TssB and VipB/TssC (eg. V. cholerae, P. aeruginosa) form a…
VipA/TssB and VipB/TssC (eg. V. cholerae, P. aeruginosa) form a tubular sheath
that is anchored to the various layers of the cell envelope through its
association with the T6SS transmembrane complex
what does happen when the t6ss contacts a target sell
Contact with a target cell induces contraction of the outer tube (VipA/B) and
pushes the inner tube (Hcp) & the puncturing device (VgrG) through the target
cell membrane (TM)
Assembly and mechanism of firing of the T6SS
- Assembly of the membrane complex (MC) and the baseplate (BP)
- Recruitment and docking of the BP on the MC
3-5. TssA-mediated polymerization of the tail tube/sheath tubular structure, which
is stopped when hitting the opposite membrane by the TagA stopper - Sheath contraction propels the tube/spike needle into the target; the ClpV
ATPase is recruited to the contracted sheath to recycle sheath subunits - Needle components and effectors are delivered inside the target.
the t6ss of paeruginosa exports…
the tse effector proteins
tse2 is the ….
toxin component of the toxin immunity system tse2/tsi2
T6SS-mediated injection of Tse2 into
bacterial cells lacking
T6SS-mediated injection of Tse2 into
bacterial cells lacking the Tsi2
immunity protein results in growth
arrest!
what does tsi2 do
Tsi2 is an essential protein in P.
aeruginosa as it provides protection
from the toxic activity of Tse2
- ie. Tse2 targets other species in
the environment
T6SS appear to be key players in ….
inter-bacterial competition in
mixed microbial communities such as biofilms, microbiome
Tse2 is structurally related to
Tse2 is structurally related to ADPribosylating toxins (covalently
transfers ADP-ribose from NAD to
host proteins in the cytoplasm)
what are Tse1 & Tse3
-are lytic enzymes that
hydrolyze PGN in the periplasm of
target cells
- Tsi1 & Tsi3 are the self-immunity
proteins in this case
Tilde1 effector is with which bacteria
Salmonella enterica subsp.
Typhimurium
what does Tlde1 do
Impairs cell
division and cell envelope
integrity by cleaving PGN
precursors
what does Tldi1 do
immunity protein
Adhesion prevents physical removal of bacteria by:
- Fluids (eg. saliva, urine) that normally serve to keep bacterial numbers low at
mucosal surfaces (mouth, small intestine and bladder) - Peristalsis (colon)
- Coughing/ sneezing (respiratory tract)
There are two main types of bacterial adherence:
i) mechanism involving pili (or fimbrae) binding to specific host cell surface
molecules, usually carbohydrates (glycolipid or glycoprotein based receptors)
ii) mechanism involving afimbrial adhesins that mediate tight binding between
bacteria and host cells. These are surface proteins that are not organized in a
filament-like structure but instead are embedded in the cell surface
Assorted flagella, pili +
adhesins are required by
Assorted flagella, pili +
adhesins are required by UTI causing bacteria for
colonization & migration to
bladder and then kidneys
Many adhesins are also…
invasion factors (“invasins”). ie. binding triggers a
signaling/ phagocytic event to promote bacterial uptake
The best characterized mode of adherence involves….
pili
what are pili
Long, non-flagellar appendages at the cell surface, that are present in a wide
range of Gram-negative and Gram-positive bacteria
* Flexible, cylindrical structures composed of polymerized pilin proteins
* These are critical virulence factors for many bacterial pathogens
* Pili mediate contact between bacteria and host cells during infection, between
bacteria and other surfaces (eg. surgical devices), or between neighboring
bacteria
Ø eg. conjugative pili facilitate horizontal transfer of DNA. Other pili mediate
microcolony or biofilm formation.
how many pili have been discovered
> 30 different pili have been identified in various E. coli strains, which
mediate host and tissue-specific interactions (“tropism”)
In many cases, the pilus/ host receptor interaction is mediated by a
specialized
tip consisting of pilin proteins distinct from that of the main pilus rod
- In other cases, binding is via by the main pilin protein itself
what are the 5 known types of pili in gram - bacteria
-chaperone-usher pili
- type IV pili (T4P)
-conjugative type IV secretion
pili
-curly fibres
- type V pili
Chaperone - usher pili are commonly expressed on
on the surface of many gram - bacteria
how many types of chaperone usher pili does upec use
-Type 1 pili
mediate interactions with the bladder
-P pili target the kidney. Both
contribute to the ability of UPEC to ascend from the bladder to the upper
urinary tract during infection
Type 1 and P pili are assembled from
Type 1 and P pili are assembled from distinct pilin subunits that are encoded in
the fim and pap operons, respectively
At their tip, both type 1 and P pili contain an
-adhesin protein
- FimH for type 1 pili and PapG for P pili
Pilins are transported across the inner membrane by the
sec pathway
In the periplasm, a chaperone (give the name and what it does)
In the periplasm, a chaperone (FimC or PapD) facilitates pilin folding and
stabilization.
The chaperone-pilin complexes are transported across the
periplasm to an OM -embedded usher (FimD or PapC), at which point pilin polymerization occurs.
Type 1 pili are produced by
…% of UPEC isolates
80%
Typically, UPEC cells have … -
… fimbriae on their surface
200-5000
A single type 1 pilus is made
up of ~1000 copies of the
major subunit …..
FimA
what does type 1 pili do
Type-1 pili connect the UPEC
outer membrane (OM) and
host cell membrane
UPEC variably produces up to …. different adhesins
16
Type-1 pili (fim genes) Bind to ….
mannose residues of glycoproteins during
colonization of the bladder epithelium
Pyelonephritis-associated (P) pili (pap genes) bind to ….
Galα1-4Galβ disaccharide present on
glycosphingolipids of the kidney epithelium
s pili buind to
sialic acid residues
Afa/Dr adhesins bind. to
decay-accelerating protein (hDAF; CD55)
and carcinoembryonic antigen cell adhesion
molecules (hCEACAMs). Frequently found in E.
coli causing pyelonephritis in pregnant women.
Type-1 pili consist of a helical rod made up of …..
repeating FimA
subunits and a tip containing two adaptor proteins (FimF and
FimG) and the adhesin FimH
FimH consists of two domains:
a lectin (adhesin)
domain & a pilin domain
the adhesin domain in fimH has a ….
Adhesin domain has a binding pocket that
accommodates D-mannose
true or false: FimH adhesin mediates invasion/ colonization
true
E. coli K12 (non-invasive) expressing ……
type-1 or P-pili can
adhere to bladder epithelial cell line
true or false: Only K7 cells expressing type-1 pili can invade
false: Only K12 cells expressing type-1 pili can invade
Latex beads coated with FimH + FimC
(chaperone; maintains…
native FimH
structure) complexes are internalized
by bladder epithelial cells
true or false: Beads coated with FimC alone or BSA
are not internalized
true
true or false; fimH is not sufficient to mediate uptake
false: it is sufficient
Binding of FimH to host cell receptors
activates …….
Binding of FimH to host cell receptors
activates signal transduction
pathways to trigger bacterial uptake
selective depletion of e.coli from the gut by. a…..
fimH antagonist
-it fucks with the intestinal colonization
