NalP: Difference between revisions

== Integration of the Translocator Domain into Outer Membrane ==

Omp85 has been found in many studies to help integrate beta barrels into the outer membrane in order to allow the autotransporter to complete its duty. Do to the hydrophilic nature of the beta barrel’s hairpin loops on the extracellular side in NaIP it is impossible for it to breach the cell membrane that is highly hydrophobic. Research of how this occurs in Neisseria meningitides is ongoing and has not been discovered yet. Yet there are many implications that a protein named Omp85 is most likely the helper protein that facilitates this. The large hydrophilic loops on the auto transporter domain might act as a recognition signal for the Omp85 complex to encompass the end of the beta barrel. From here the Omp85 complex which sits on the paraplasm side of the cell membrane is activated and creates a pore and place the beta barrel within the membrane, whilst avoiding that hydrophilic loops from directly coming in contact with the hydrophobic cell membrane. Then the Omp85 molecule is able to integrate the beta barrel into the pore that it created situating it permanently there. The lag time between Omp85 and the translocater exporting a protein is very small and is hard to tell wether they can or only occur simultaneously. <ref name="PMID: 8254661" />

 

 

 

 

Omp85 has been found in many studies to help integrate beta barrels into the outer membrane in order to allow the autotransporter to complete its duty. Do to the hydrophilic nature of the beta barrel’s hairpin loops on the extracellular side in NaIP it is impossible for it to breach the cell membrane that is highly hydrophobic. Research of how this occurs in Neisseria meningitides is ongoing and has not been discovered yet. Yet there are many implications that a protein named Omp85 is most likely the helper protein that facilitates this. The large hydrophilic loops on the auto transporter domain might act as a recognition signal for the Omp85 complex to encompass the end of the beta barrel. From here the Omp85 complex which sits on the paraplasm side of the cell membrane is activated and creates a pore and place the beta barrel within the membrane, whilst avoiding that hydrophilic loops from directly coming in contact with the hydrophobic cell membrane. Then the Omp85 molecule is able to integrate the beta barrel into the pore that it created situating it permanently there. The lag time between Omp85 and the translocater exporting a protein is very small and is hard to tell wether they can or only occur simultaneously. <ref name="PMID: 8254661" />

Interesting questions were raised on how the alpha helix in the center of the beta barrel effected the mechanism of protein transportation out of the cell. The first step to understanding what shapes of proteins can move though the pore was figured by trying to move a disulfide bond through the pore. This was unsuccessful and led to part of the understanding that the only way that proteins can move though this pore was by being completely unfolded. Yet once inside of the extracellular material the protein must be folded. Knowing these two crucial pieces of data it was clear that as the protein passes through the pore it is folded, and due to the C-terminal end's placement on the periplasmic side of the pore it was highly unlikely that was the participating portion that effected the change in conformation of the protein as it passes through. Oppositely the N-terminal side of the pore lies on the alpha helix facing the extracellular matter, placing it in prime location to change the conformation of the passing protein. Another possible place where interaction could occur between the passing protein and the pore would be at a large hairpin loop that is on the extracellular side of the pore. This would also provide a prime placement for initiation of protein folding.<ref name="NaIP" />

The Threading Model could be one possible model that would allow for transportation of passenger proteins out of the cell and into extracellular material. The model has one single strand of protein entering and as it crosses to the other side it begins to fold starting with it’s n-terminus. The Threading Model is a possible explanation for how a protein would able to fit through the narrow gap that the beta barrel and alpha helix provide. The threading model allows for one strand of the DNA to pass through the pore without being sterically hindered by the size of the alpha helix that blocks the beta barrel. Yet there are reasons why this is an unlikely model. One major reason why this seems implausible is that other research that has been done on autotransporters has shown that the last thing to leave the pore of the passenger protein is the n-terminus. So therefore how would the n-terminus start the folding if it is the last thing to leave? This also means that the autotransporter would have to secrete something in order to allow for attraction of the n-terminus side toward the pore. This was unable to be shown in in artificial passenger proteins.<ref name="NaIP" />

One alternative theory argues that the beta barrel is actually not used as a protein secretion pore at all. As Omp85 compasses then end of the beta barrel it travels toward the cell membrane as if to place the autotransporter into the cell membrane yet instead of placing it, Omp85 continues through into the extracellular material. As the translocator is being carried toward the cell membrane it is able to pick up a passenger protein using its loose c-terminus end that would have faced inward toward the paraplasm. Then all three the, Omp85, translocator, and the passenger protein are all transported to extracellular material through the pore that Omp85 is able to create. Then they all dissociate away from one another, which frees the passenger protein. This is another possibility for how the translocator is able to transport passenger protein out of the cell yet changes the view of the translocator all-together. If this is in fact the way that passenger proteins leave the cell then NaIP is no a autotransporter at all. Autotransporter just as it sounds autotransports, meaning that the protein pulls itself through as it is folded on the opposite side of the cell. As plausible as this seams it would mean a major change in the way that this translocator protein is classified. <ref name="NaIP" />