Bacterial Transport System Flashcards
What is the structure of most transport proteins in the outer membrane of gram -tve bacteria?
B-barrel structure
What is the B-barrel formed of?
8-26 B-strands
What are the 3 main entrances for transport across the outer membrane?
Porins
Specific channels
High-affinity transport systems
What is the general structure of porins?
Trimeric structure
What the most abundant porins in E.coli?
OmpC
OmpF
PhoE
Which porins transport cations?
OmpC and OmpF
What porins transport anions?
PhoE
What are specific channels?
Similar structure to porins, but allow for the transport of specific nutrients (e.g. maltose)
Are specific channels passive or active?
Passive, although they accelerate the diffusion of solutes at low concentrations
What is an example of a specific channel?
LamB in E. coli, which transports maltose
What is the structure of LamB?
Trimeric 18 stranded B-barrel
What are some features of high-affinity transport systems?
High higher affinity for their substrates
Transport requires energy (active)
What are some examples of substrates transported via high-affinity transport system?
Iron
Vitamin B12
How is energy generated for high-affinity transport system?
Proton motive force, by coupling transporters with proteins at inner membrane
What is the outer membrane receptor for vitamin B12?
BtuB
What is the outer membrane receptor for iron?
FhuA
What is the structure of most transport proteins in the inner membrane of bacteria?
A-helix structure
What are the 3 class of cytoplasmic membrane-transport systems?
Simple transporters
ABC transporters
Group translocation
Are all inner membrane-transporting systems passive?
No, they are all active
Where do simple transporters get their energy from?
Proton motive force- secondary active transport
Where do ABC transporters get their energy from?
ATP
Where does group translocation get its energy from?
PEP
What makes up simple transporters?
Single proteins that span the membrane. They are either symport or antiport transporters
What is symport transport?
Transport of two molecules in the same direction
What is antiport transport?
Transport of two molecules in opposite directions across the membrane
What is the LacY permeate transporter?
Symport simple transporter, which transports lactose and H+ in the same direction
What is the sodium-proton transporter
Antiport simple transporter, which transports sodium and H+ in opposite directions across the membrane
How many ABC transporter does E. coli contain?
Approximately 80
What 3 components make up ABC transporters?
Substrate binding domain (SBP)
Transmembrane domain protein (TMD)
Nucleotide binding domain protein (NBD)
What is the role of the SBP in ABC transporters?
SBP binds to substrate using Venus flytrap mechanism, inducing a conformational change
SBP interacts with TMD protein (periplasmic end) and releases the substrate
What is the role of TMD in ABC transporters?
Substrate is transferred across transmembrane through TMD protein
What is the role of NBD in ABC transporters?
Energy for transfer is generated by hydrolysis of ATP by NBD protein (acts as ATPase)
What is group translocation made up of?
A series of proteins (e.g. phosphotransferase system of E. coli consists of 24 proteins )
What molecules are group translocated?
Commonly sugars like fructose, glucose and mannose
How does group translocation work?
The proteins in the system are alternatively phosphorylated and dephosphorylated until the final membrane-spanning protein receives the phosphate group and phosphorylates the sugar to be transported
