Lecture 4 Flashcards
P-type ATPases
Consist of large alpha (200kDa) and associated beta subunits
Pump cations
Inhibited by orthovanadate
ATP donates gamma-phosphate to aspartate during cation pumping
Na+/K+ ATPase
Located in plasma membrane of animal cells
3Na+/2K+ per ATP hydrolysed
Maintains high K+/low Na+ in cytosol
Maintains Na+ electrochemical gradient
Structure of Na+/K+ ATPase
2 alpha (112kDa) and 2 beta (34kDa) subunits
Fungal and Plant H+ ATPase
Location - Plasma membrane of plants and fungi
Stochimetry of 1H+ per ATP
Expels excess H+
H+ electrochemical gradient maintained for H+ coupled transport
Mainatains negative transmembrane voltage
Regulates cytosolic pH
Loosens cell wall by acidification
Structure of fungal and plant H+ ATPase
1 alpha subunit (112kDa)
Sarcoplasmic endoreticulum Ca2+ ATPase
- Located in sarcoplasmic reticulum in muscle cell cytoplasm
- 2Ca2+/ATP
Restores low Ca2+ after muscles contract
1 alpha subunit (112kDa) - 3 isoforms
Name inhibitor of sarcoplasmic endoreticulum Ca2+ ATPase
Thapsigargin
Plasma membrane Ca2+ ATPase
Location is plasma membrane in animals, plants, fungi
1-2Ca2+/ATP (in exchange for H+)
Maintains low cytosolic calcium ion as otherwise cytotoxic
Cell signalling
Structure is 1 alpha subunit
Gastric mucosal H+/K+ ATPase
Location: gastric epithelial cell plasma membrane
2H+/2K+ per ATP
H+ secreted into lumen of stomach
2 alpha and 2 beta subunits
Structure of P-type ATPases
N-terminus - 4 TMS domains - give rise to 4 stalk domains
C- terminus - 6 TMS domains - gives rise to 5th stalk domain
Most of pump in cytoplasm
What are the 3 regions of P-type ATPases
Region B - Conformational changes in ion binding site
Region C - Phosphorylation site/Nucleotide binding site
Region J - Comprises hinge to allow cytosolic regions to move and interact
What do conformational changes induce in cation binding?
Binding of ions at low concentration
Dissociation of ions at high concentration
SERCA Ca2+ ATPase
ATP hydrolysis + phosphorylation of aspartate
Head regions move
E1 to E2
Alters affinity
Binding site exposed to lumen of SR
CPx pumps
Transport toxic and nutrient metal (Cu, Pb, Zn, Cd)
First identified in Enterococcus (COPA and COPB)
What’s Menkes disease
Systemic copper deficiency
What’s Wilsons disease
Excessive copper accumulation in liver
CPx vs P-type pump
N-terminus - 6 TMS domains, cysteine repeats
x in CPx can be serine, histidine, or cysteine
C-region: conserved histidine-proline
C-terminus - less TMS domains (2)
V-type pumps
Almost exclusively H+ ATPases on intracellular membranes of eukaryotic cells
Explain rotational catalysis
ATP hydrolysis by A3B3 complex
Torque generated in D-subunit
Ring of 6 ‘c’ subunits rotates
H+ translocation through V-pumps
ATP binding cassettes (ABC)
Superfamily of transporters
Energy from ATP used to transport solutes in and out
Where are ABC superfamily important
Cystic fibrosis
MDR transporters - pathogen and cancer cell drug resistance
Structure of ABC transporters
N-terminus - 6 TMS domains
C-terminus - 6 TMS domains
Each 6 joined by ATP
ABC conserved motif
GX(S/T)GXGK(S/T)(S/T)
Explain flippase model of ABC transporters
Lipid soluble molecule diffuses into cytosolic facing leaflet of plasma membrane
Binds MDR1 protein
Substrate flipped by ATP hydrolysis to exoplasmic leaflet of plasma membrane
Substrate molecule diffuses into extracellular space
