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TolB | <StructureSection load='' size='350' side='right' scene='TolB/Tolb/1' caption='E. coli TolB (PDB code [[1c5k]])'> | ||
==Structure== | ==Structure== | ||
TolB is a 44-kDa periplasmic protein associated with the outer membrane. It has two domains: an N-terminal α/β domain and a C-terminal six-bladed β-propeller (to which [[Pal]] and [[Colicin E9]] bind) <ref>PMID: 19696740</ref>. The β-propeller has a latching or ‘Velco’ strand which joins the first and last of the six blades, and is positioned in the domain-domain interface. When Pal binds to the C-terminus of TolB, the latching strand moves away from the interface and carries with it a proline residue. The movement of the latching strand opens up a canyon that would normally be buried between the N- and C-terminal domains of TolB. This canyon can now be used as a binding site for the N-terminal of TolB, which forms a helical half-turn and a β-sheet against the canyon. | '''TolB''' is a 44-kDa periplasmic protein partially associated with the outer membrane<ref name='Bouveret'>PMID: 7744736</ref>. It has two domains: an N-terminal α/β domain and a C-terminal six-bladed β-propeller (to which [[Pal]] and [[Colicin E9]] bind)<ref name='Bonsor'>PMID: 19696740</ref>. The β-propeller has a latching or ‘Velco’ strand which joins the first and last of the six blades, and is positioned in the domain-domain interface. When Pal binds to the C-terminus of TolB, the latching strand moves away from the interface and carries with it a proline residue. The movement of the latching strand opens up a canyon that would normally be buried between the N- and C-terminal domains of TolB. This canyon can now be used as a binding site for the N-terminal of TolB, which forms a helical half-turn and a β-sheet against the canyon. For additional details see [[Tol]]. | ||
==Function== | ==Function== | ||
The distal N-terminal 12 residues of TolB has two conformational states which are governed by protein-protein interactions with the β -propeller and results in the binding of TolA in the inner membrane. | The distal N-terminal 12 residues of TolB has two conformational states which are governed by protein-protein interactions with the β -propeller and results in the binding of [[TolA]] in the inner membrane<ref name='Bonsor'>PMID: 19696740</ref>. | ||
= | TolB has been shown to be essential for the function of the [[Tol]] system in ''Escherichia coli''<ref name='Bonsor'>PMID: 19696740</ref> by generating an allosteric signal based on a conformational switch in the β-propeller region. TolB has also been shown to interact with the porins of Escherichia coli, in particular OmpF, OmpC, PhoE and LamB, but not OmpA or any of their denatured counterparts. It has been proposed that the whole Tol complex plays a role in this association, although "tol" mutants do not prevent this assembly completely therefore the Tol system may be involved kinetically, not directly<ref>PMID: 9393690</ref>. | ||
==The TolB-Pal Complex== | |||
The TolB-[[Pal]] complex is involved in maintaining the outer membrane integrity. Upon binding, TolB and Pal undergo a conformational change , the result of which is crucial for further interactions with other proteins<ref name='Godlewska'>PMID: 19519769</ref>. This complex is parasitised by protein antibiotics and disrupted in order to trigger the translocation of the toxin across the outer membrane (see [[Colicin]] for further information)<ref name='Bonsor'>PMID: 17375930</ref>. | |||
To study the interaction of TolB with Pal, two studies were carried out<ref name='Bouveret'>PMID 7744736</ref>: TolBBep (tagging TolB for immunoprecipitation), which allows the associated proteins to remain in contact with TolB, and ''in vivo'' cross-linking experiments with formaldehyde. Immunoprecipitation gave the result that Pal co-precipitates with TolBBep, while the cross-linking showed that in the present of Pal, the two products migrated close to each other, but in the absence of Pal, neither band was present, demonstrating an interaction between the two. These two experiments showed that TolB directly interacts with Pal, and that this interaction is responsible for maintaining the association of TolB with the membrane. | |||
{{STRUCTURE_2hqs| PDB=2hqs | SIZE=300| SCENE= |left|CAPTION=E. coli TolB (cyan) complex with peptidoglycan-associated lipoprotein (gold), acetate, sulfate and glycerol, (PDB code = [[2hgs]]) }} | |||
</StructureSection> | |||
==3D structures of TolB== | |||
Updated on {{REVISIONDAY2}}-{{MONTHNAME|{{REVISIONMONTH}}}}-{{REVISIONYEAR}} | |||
[[1crz]], [[1c5k]] – EcTolB – ''Escherichia coli''<br /> | |||
[[2ivz]] – EcTolB + colicin-E9 T-domain<br /> | |||
[[4jml]] - EcTolB (mutant) + colicin-E9 T-domain (mutant)<br /> | |||
[[7nst]] - EcTolB (mutant) + colicin-E9 + outer membrane protein F – Cryo EM<br /> | |||
[[7nsu]] - EcTolB (mutant) + colicin-E9 + outer membrane protein F + BtuB – Cryo EM<br /> | |||
[[3iax]] - EcTolB + colicin-A translocation domain<br /> | |||
[[2hqs]], [[2w8b]] - EcTolB + peptidoglycan-associated lipoprotein<br /> | |||
[[4pwz]] – YpTolB – ''Yersinia pestis''<br /> | |||
[[4r40]] - YpTolB + peptidoglycan-associated lipoprotein<br /> | |||
[[6pnv]] – TolB – ''Salmonella enterica''<br /> | |||
[[7mx5]] – TolB – ''Acinetobacteria baumannii''<br /> | |||
== References== | == References== | ||
<references/> | <references/> | ||
[[Category: Topic Page]] | |||