Lect 4: Membrane Transport cont.

4 Types of ATPases

1. P-class = moves _____

2. V-class = moves _____, uses/makes ATP

3. F-class = moves _____, uses/makes ATP

4. ABC Transporter = moves _____

4 Types of ATPases

1. P-class = moves small ions

2. V-class = moves H+, uses ATP

3. F-class = moves H+, uses OR makes ATP (both directions)

4. ABC Transporter = moves substances (nutrients, drugs, etc.)

P-Class 2 main examples:

1. __________

2. __________

P-Class 2 main examples:

1. Ca2+ ATPase

2. Na+/K+ Pump

P-class examples:

1. Ca2+ ATPase = moves Ca2+ with/against concentration gradient

   • in ________ cells

   • SR lumen/cytosol to SR lumen/cytosol

   • contains ___ Ca2+-binding sites

P-class examples:

1. Ca2+ ATPase = moves Ca2+ against concentration gradient

   • in muscle cells

   • cytosol to SR lumen

   • contains 2 Ca2+-binding sites

Ca2+ ATPase Mechanism

• E1/E2 is more stable than E1/E2

-

1. ____ and ____ bind to transporter

2. ____________ = energy is released (and Pi added)

3. Conformational change (E1/E2 → E1/E2)

   • now has low affinity for Ca2+

4. ____ is released

5. ____ is released

6. Conformational change (E1/E2 → E1/E2)

   • now has high affinity for Ca2+

Ca2+ ATPase Mechanism

• E1 is more stable than E2

-

1. ATP and Ca2+ bind to transporter

2. ATP hydrolysis = energy is released (and Pi added)

3. Conformational change (E1 → E2)

   • now has low affinity for Ca2+

4. Ca2+ is released

5. Pi is released

6. Conformational change (E2 → E1)

   • now has high affinity for Ca2+

P-class examples:

2. Na+/K+ Pump = moves Na+ with/against gradient, and moves K+ with/against gradient

   • maintains ___________

   • Na+/K+ move in same/opposite directions

   • contains ___ Na+-binding sites and ___ K+-binding sites

P-class examples:

2. Na+/K+ Pump = moves Na+ against gradient, and moves K+ against gradient

   • maintains membrane potential

   • Na+/K+ move in opposite directions

   • contains 3 Na+-binding sites and 2 K+-binding sites

Na+/K+ Pump Mechanism

1. ____ and ____ bind to transporter

2. ____________ = energy is released (and Pi added)

3. Conformational change (E1/E2 → E1/E2)

   • now has low affinity for ____ and high affinity for ____

4. ____ is released and ____ binds

5. ____ is released

6. Conformational change (E1/E2 → E1/E2)

   • now has high affinity for ____ and low affinity for ____

7. ____ is released

Na+/K+ Pump Mechanism

1. Na+ and ATP bind to transporter

2. ATP hydrolysis = energy is released (and Pi added)

3. Conformational change (E1 → E2)

   • now has low affinity for Na+ and high affinity for K+

4. Na+ is released and K+ binds

5. Pi is released

6. Conformational change (E2 → E1)

   • now has high affinity for Na+ and low affinity for K+

7. K+ is released

V-Class Pump

• uses/makes energy (via _____________) to move H+ with/against concentration gradient

• critical in (disease)

  • help move H+ into ________

  • V Pump issue → ?

V-Class Pump

• uses energy (via ATP hydrolysis) to move H+ against concentration gradient

• critical in osteopetrosis

  • help move H+ into resorption lacuna

  • V Pump issue → low H+ in lacuna → osteopetrosis

F-Class Pump

• uses/makes energy (via _____________) to move H+ with/against concentration gradient

• aka __________

F-Class Pump

• uses energy (via PE gradient of H+) to move H+ against concentration gradient

• AND makes energy by moving H+ with concentration gradient

• aka ATP synthase

ABC Transporter = moves different substrates across membrane

• ___ specific aa sequences bind and hydrolyzes ATP

ABC Transporter = moves different substrates across membrane

• 2 specific aa sequences bind and hydrolyzes ATP

ABC Transporter Mechanism

1. __________ interacts with __________ → complex

2. complex interacts with (open/closed) channel

3. conformational change

4. __________ provides energy → channel opens/closes + solute moves inside

ABC Transporter Mechanism

1. solute/nutrient interacts with solute-binding protein → complex

2. complex interacts with (closed) channel

3. conformational change

4. ATP hydrolysis provides energy → channel opens + solute moves inside

Channels and Transporters examples:

Channels

1. _________

Transporters

1. _________ = uniporter

2. _________ = symporter

Channels and Transporters examples:

Channels

1. Aquaporin

Transporters

1. GLUT1 = uniporter

2. Na+/Glucose Transporter = symporter

Channels

• ___________ = transport H2O down conc. gradient

  • gated/non-gated

  • conformational change?

  • water forms _________ with hydrophilic aa

Channels

• Channels

  • Aquaporin = transport H2O down conc. gradient

    • non-gated

    • NO conformational change

    • water forms H-bond with hydrophilic aa

Transporter

• ex: ___________ = uniporter, brings glucose into brain

  • located on ___________

• ex: ___________ = symporter, Na+ with/against gradient and glucose with/against gradient

Transporter

• ex: GLUT1 = uniporter, brings glucose into brain

  • located on endothelium (blood vessel lining)

• ex: Na+/Glucose Transporter = symporter, Na+ with gradient and glucose against gradient

GLUT1 vs GLUT4

• GLUT1/GLUT4 brings glucose into brain, GLUT1/GLUT4 brings glucose into muscle/fat cells

• GLUT1/GLUT4 is a uniporter, GLUT1/GLUT4 is a uniporter

• GLUT1/GLUT4 is insulin-dependent, GLUT1/GLUT4 is insulin-independent

• GLUT1/GLUT4 deficiency → diabetes, GLUT1/GLUT4 deficiency → neuro issues

GLUT1 vs GLUT4

• GLUT1 brings glucose into brain, GLUT4 brings glucose into muscle/fat cells

• GLUT1 is a uniporter, GLUT4 is a uniporter

• GLUT4 is insulin-dependent, GLUT1 is insulin-independent

• GLUT4 deficiency → diabetes, GLUT1 deficiency → neuro issues

All 3 Together (Amino Acid Import)

All 3 Together (Amino Acid Import)

1. Pump: Na+/K+ ATPase Pump = creates Na+/K+ concentration gradient

2. Channel: K+ channel = K+ flow down concentration gradient

3. Transporter: Na+/Lysine symporter = Na+ flows down electrochemical gradient → powers uphill transport of Lysine

Click Questions

1. What is a major difference between V-ATPase and F-ATPase?

2. Why can’t H3O+ flow through an aquaporin channel?

3. How would the F-ATPase be affected if H3O+ could flow through aquaporins?

1. What is a major difference between V-ATPase and F-ATPase?

   • V-ATPase = against gradient, need ATP

   • F = uses gradient to create ATP, can work in reverse direction (so also can use ATP to move H+)

2. Why can’t H3O+ flow through an aquaporin channel?

   • charge - aquaporins contain positive residues → repel protons

3. How would the F-ATPase be affected if H3O+ could flow through aquaporins?

   • H+ gradient would disappear → F+ ATPase would have no force → ATP production would stop

Click Questions

4. How does secondary active transport differ from active transport?

5. What transport proteins use active transport & what transport protein use secondary active transport?

6. Do channels and uniporters require energy input? Why?

Click Questions

4. How does secondary active transport differ from active transport?

   • secondary active = energy is from ion gradient PE

   • active = energy is from ATP 

5. What transport proteins use active transport & what transport protein use secondary active transport?

   • symporters and antiporters = secondary active

   • atpase (abc transporters, etc.) = active

   • F = depends on direction, can be active or facilitated 

6. Do channels and uniporters require energy input? Why?

   • channels + uniporters do not require energy input

   • things flow down conc. gradient

Click Questions

7. GLUT1 vs GLUT4?

Click Questions

7. GLUT1 vs GLUT4?

   • brain vs muscle 

   • already in plasma membrane vs stored inside cell, later moved to plasma membrane in response to insulin

   • glut1 deficiency ⇒ brain issues

   • glut4 deficiency ⇒ diabetes