Lecture 9: A tale of two transport systems Flashcards
Why is iron important?
oxygen storage and transport, electron
transfer and acid–base reactions in biology.
GReat oxygen event: The mass extinction forced evolution of organisms that could master a
new challenge?
: Fe3+ insolubility.
Why you need active transport for uptake of Fe-siderophore complexes ?
iron is rare, so by diffusion you won’t ever find a complex probably. Need active transport.
How do you transport Fe-siderophore complexes across the O membrane? E. coli: Specific receptor is required with plug for binding. It contacts what?
The receptor is contacting an inner membrane protein:
TonB
(‘Ton-B dependent receptors’)
Energy for this uptake is provided by two additional proteins ExbB and EbD. They are homologous to MotA and MotB ( flagella). What is their predicted function?
Therefore, ExbBD are predicted to form a molecular motor, which then also rotates TonB.
PMF is needed for siderophore transport.
Working model for TonB-dependent transport:?
> substrate binding exposes TonB box
TonB can bind to TonB box
TonB is rotated via interaction via ExbBD
rotation (partial) unfolds the plug domain
diffusion of siderophore through β-barrel
TonB receptors can also do:
Hundreds of polysaccharide degrading enzymes (specificity) can be produced by …, many secreted via Type IX secretion.
Enzymes encoded by…
Bacteroides.
PUL (polysaccharide ultilisation loci)
What is Mla for system?
Mla: one of the E. coli phospholipid transport systems. Transport from IM to OM.
What is the Mla system used for?
Maintenance of lipid asymmetry and barrier for hydrophobic molecules. Defects result in detergent sensitivity.
MlaA functions as ?
)
a channel, picking up phospholipids from the outer layer of the OM.
What happens with the phospholipids picked up by mlaA?
phospholipids Can then be picked up by the 2nd protein, MlaC chaperone. MlaC chaperone:
Acyl chains are perfectly shielded in protein environment
