Questions

Scenario of given information:

Intimin is a protein present in the membrane of E. coli O157:H7.  The translocated intimin receptor is a bacterial protein which is injected into host. Intimin binds to the translocated intimin receptor present in host cells in order to establish adherence between the bacteria and host epithelial cells.

General

When did this attachment first evolve? Do all E. coli utilize intimin and tir?  How did the bacteria initially establish that intimin would conformationally interact with the receptor? Is this attachment the only form of adherence between the cells?  How strong is the adherence?  What is the signal that initiates actin/cytoskeleton rearrangement to form the pedestal?  What is the purpose of pedestal formation?  How was it established that translocation occurs?  Does the interaction play a role other than adherence between bacteria and host?  The bacteria travel across the host membrane on these pedestals...how does this movement occur?

Intimin  

Does intimin have any other roles in the cell besides receptor recognition? Does bound intimin signal to the cell that enough receptor has been translocated?  Are intimin's binding capabilities specific for the receptor? 

Translocated Intimin Receptor

How is the protein transported to the host?  Do all E. coli utilize the same transport mechanism?  In Type III secretion, what promotes the transport of the receptor through the needle structure?  How long is the needle structure?  Does the receptor contain a signal sequence that targets it to the location of the transport complex?  Is unfolding required for translocation?  After transport, how is the receptor modified in the host?  Does it refold upon host entry?  What modifications are necessary for membrane insertion?  How do the two receptor cytoplasmic domains interact with the host cell processes?  After the initial intimin/receptor interaction, the receptors cluster underneath the bacteria.....what is the signal which promotes this receptor clustering?

Translocation of the Receptor

How is the receptor translocated from the bacteria to the host?  What other proteins are involved in initiating the translocation?  Is the translocation machinery always ready for transport?  If not, what is the signal for assembly?  How will the complex assemble?  How does this complex prevent other proteins present in the bacteria from translocating to the host?  How close does the bacteria need to be to the host?  Are shuttle proteins present in the translocation machinery?  After translocation, does the machinery retract?  What determines when translocation is complete?       

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