L14 - EPEC & enteric disease Flashcards

Question

How do EspF & MAP share a common target?

Answer 1

* Structural studies have shown that Map is GEF – it functions specifically to activate Cdc42 which triggers the signaling cascade leading to these filopodia formation * It’s also been found that EspF directly activates N-WASP as it has 3 poly proline rich regions – each one has an N-WASP binding domain – this recruits N-WASP * Found that the feature is very identical to the auto-inhibitory domain in N-WASP, it binds & opens N-WASP to activate it – makes it constitutionally active to drive actin nucleation events * Also found that N-WASP has recruitment sites for a protein called SNX9 which is linked the recruitment of the endocytic machinery to internalize the membrane * Illistrates the knowledge of the bacteria

Answer 2

Tir, Intimin, Map and EspF cooperativity removes major water pump from intact microvilli The rapid onset of watery diarrhoea is related to the SGLT1

Answer 3

* When you infect with EPEC there is a rapid loss of SGLT1 from the apical surface * Effector molecules work together to remove SGLT1 from the surface * We think EspF is recruiting SNX9 in N-WASP to drive endocytosis - & the other effector molecules must be part of this process * We know that the EspG LEE effector can prevents secretory pathways – prevents new SGLT1s being added to the microvilli * This causes the rapid onset of watery diarrhea

Answer 4

* EPEC disrupts cell-cell junctions in vitro and in vivo models – this allows antigens such as flagellin (key stimuluses of inflammation) to get between the cells & interact with its TLR, TLR5 * This then triggers signalling cascades that leads to the activation of transcription factors to trigger the expression of cytokines such as IL-8 which act as alarm calls to recruit PMNs to the site of infection so they can start attacking the bacteria * These should lead to the release of more chemokines which leads to an inflammatory diarhhoeal disease * EPEC diseases are not associated with a strong inflammatory response which suggests there is a suppressive mechanism

Answer 5

NleC was found to interact with NF-kB in the nucleus and was able to cleave it as it is a metalloprotease The complex was recruited by docking at the NleC and then has a catalytic domain that cleaves NF-kB to stop it being functional Loss of IκB and NF-κB Rel proteins p65 and p50 When they looked at the crystal structure of NleC, it mimics the target of NF-kB Again illustrates how bugs understand the physiology & can mimic the DNA

Answer 6

* RPS3 directs NF-kB to specific genes * Its been found that to the effector molecules, that the pathogens look like serine-threonine kinases – have stolen the structure & put a signal sequence on it & delivered it back into the host to utilize it against the host * Found that the molecule interferes with the function of ribosome binding protein S3 although doesn’t require kinase activity * Also found that NleH could interfere with the function of RPS3 * Illustrates that bacteria have the ability to alter specific proteins that hinder the replication pathway

Answer 7

They can target other effector molecules that cleave other molecules NleCs will go and cleave JNK & p38 – because they recognize the loop structure – a residue difference in ERK protects ERK from being degraded However, ERK is stopped by other effector molecules

Answer 8

Another target molecule targets the gene upstream from that – TAB proteins They are important for activating the kinase NleE catalyses the cysteine methylation of these 2 TAB proteins – prevents capacity of proteins to recruit TAK1

Answer 9

Another effector molecule that targets the upstream protein TRAF6 Tir can target these proteins & lead to their degradation and other TRAFs which are associated with cytokine signaling Tir also has other functions to inhibit the pathway – some residues on the C-terminus that are phosphorylating by the host & act as an ITIM, which recruits phosphatase to inhibit TRAF function so it doesn’t get ubiquitinated so cannot recruit the TABs – inhibits NF-kB signaling

Answer 10

NleB targets proteins quite high in the pathway Can inhibit signaling though receptor kinases but not through antigens like the TLRs suggesting its targeting something upstream of these pathways NleB targets a specific component upstream, causing the modification of these domains – TRA domains Adds a sugar onto arginine (novel modification) on the TRA domain which inhibits its activity The target arginine is conserved in multiple proteins involved in regulating cell death pathways

Answer 11

EspL is a cysteine protease effector molecule that targets proteins with the rim motif Found in lots of different molecules & important in signaling through NF-kB & also protects the cell death signaling pathways

Answer 12

if you over inhibit one pathway, the cell recognizes that and causes dysfunction leading to cell death • The bacteria understand this • They target lots of proteins at low levels to inhibit their activity a little bit – doesn’t impact any individual step but collectively they inhibit signaling to NF-kB • The levels of delivery are critical • Also gives the bacteria evolutionary advantages No pathogen wants to kill its host, it just wants to have a maximal level where it can propagate before its killed by the cell Can lead to oversignalling & death if you're immunocompromised or if the pathogen is extra virulent

L14 - EPEC & enteric disease Flashcards

(36 cards)