3.1 Transporters (ATP-driven Pumps) Flashcards
F-type ATPase
catalyze uphill passage (intermembrane space to cytosol) of proteins with ATP hydrolysis (makes ATP)
structural subunits of F-type ATPase
Fo - provides transmembrane pathway - subunit a (proton half-channels) - subunit b (arm) F1 - uses energy of ATP to drive protons uphill - subunit c (proton binding site)
steps of proton translocation (5 steps)
1) proton from periplasmic space move towards half-channel with - Asp
2) proton fills empty proton-binding site and displaces Arg side chain, swings over to filled proton-binding site on subunit c. Proton at next site is displaced
3) displaced proton moves through half-channel II,and exits into matrix
4) counterclockwise rotation of entire c ring moves empty c subunit over half-channel I
5) process repeated
does F-type ATPase do uphill or downhill transport
uphill transport of protons
F-class proton pumps found in (3)
1) bacterial PM
2) inner mitochondrial membrane
3) thylakoid membrane of chloroplast
V-class proton pumps found in (3)
1) vacuolar membranes in plants/yeast/fungi
2) endosomal/lysosomal membranes in animal cells
3) PM of osteoclasts+kidney tubule cells
V-class ATPase function
acidifying intracellular components (lysosome, endosomes, Golgi, secretory vesicles)
- uses ATP to pump H+
P-type ATPase function
maintain ionic differences
- phosphorylated by ATP
- includes: (Na/K antiporter, H/K antiporter, Ca2+)
concentration gradient of K+ across cell
10-30 times higher inside cell than outside
concentration gradient of Na+ across cell
10-30 times higher outside cell than inside
where is the NaK pump found
PM of all animal cells
Na+/K+ pump
ATP-driven antiporter: pumps Na+ out and K+in
SERCA
Ca2+ ATPase for muscle contraction
how does SERCA work
1) rapid influx of Ca2+ triggers opening of Ca2+ channels on PM
2) Ca2+ ATPase on SR (ER of muscle cells) pumps Ca2+ into SR and muscles can contract
SERCA structure
single polypeptide, 10 TMS
- N domain binds ATP and Mg2+
- P domain contains Asp characteristics of P-type ATPases
- A domain communicates movements between N and P domains
ABC Transporters structure
- 2 nucleotide binding sites in cytosol (homodimer or heterodimer)
- 2 transmembrane domain (can vary in length)
- binding site for 2 ATP
ABC Transporter function
transport of sugars, vitamins, amino acids, etc from cytosol to extracellular space (in humans)
ABC Transporter mechanism steps (3)
1) substrate from cytosol binds to inward-facing site between TMS
2) 2 ATPs bind to ATP binding sites of the 2 nucleotide binding domains
3) ATP stabilizes dimerization of NBD
4) 90 degree rotation of ABC and the substrate released in the extracellular space
5) ATP hydrolysis
6) Pi and ADP released
MalE
Maltose binding protein in gram negative bacteria: captures maltose in periplasm and brings to ABC transporter on IM
Maltose transporter
ABC transporter in gram negative bacteria
- transports maltose from periplasm space to cytosol with use of 2 ATP
for ABC transporters, how are more hydrophobic substrates handled?
more hydrophobic substrates are more embedded into the lipid bilayer
MsbA
(lipid flippase) - ABC transporter that exports a lipid from inner leaflet to outer leaflet
how was the activity of MsbA investigated with ATP
1) fluorescent phospholipids were added to membrane
2) some cells given ATP, some not
3) adding non-membrane-permeating quenching compound
4) the ones given ATP showed greater fluorescence because the flippase MsbA flipped some of the fluorescent phospholipids inside
TAP transporter
1) foreign proteins are degraded
2) recognized by TAP1 and TAP2
3) peptides translocated to ER lumen and loaded onto MHC1
4) MHC1 displayed on PM for macrophages to kill the cell
CFTR
“Cystic fibrosis transmembrane conductance regulator”. ABC transporter. But functions as Cl- channel in PM of epithelial cells. Cl- from cytosol to outside
- maintains normal salt concentrations of the mucous layer of the airway for proper hydration so cilia can remove bacteria from air we breathe
what does the R-domain the CFTR do?
regulatory region that controls channel activity of the transporter by blocking the entry door of the channel (Cystic fibrosis transmembrane conductance regulator). Always found in cystic fibrosis
cystic fibrosis
common hereditary disease where the normally thin layer of mucus that coats the internal surface of the lungs is unusually thick and sticky due to accumulation of bacterial infections because the cilia can’t remove the bacteria from the mucous layer
