1. Alpha Helices Compose the Integral Protein Bacteriorhodopsin
Bacteria light-harvesting protein that generates proton gradient
α-Helix most common 2° membrane structure
Helical (yellow) and charged (red) residues

2. Hydropathy Plots Identify Potential Trans-Membrane Peptide Regions
Hydrophobicity
Index: the
free energy needed to transfer successive segments of a polypeptide
from a non-polar solvent to water
Hydropathy Plot

3. Porins – beta Barrel Trimers
Located in outer membranes of bacteria, mitochondria and chloroplasts
Always open allowing solutes to travel through in either direction; referred to as passive transport

4. Bacterial Channel - Porin
Beta barrel with a hydrophobic exterior and a hydrophilic core
Hydrophobic (yellow) and hydrophobic (white) residues shown

5. Transport Protein Classification by Operation
Does not specify active or passive transport
Single substance versus coupled movement in the same or opposite direction

6. Highly-Selective Potassium Channel
10,000 times more selective to K+ than Na+

7. Size Selective Channel Only Allows Potassium Ion Passage
K+ movement:
Down the concentration gradient
From cytosol to cell exterior
Cell exterior
Cytosol

8. Selectivity Filter Determines the Preference of K+ Over Other Ions
Two of four trans-membrane alpha helices shown
Dehydrated K+ ions move across the membrane
Ionic diameter K+ = 2.66 Å and Na+ = 1.9 Å
Why does Na+ not move through this pore?

9. Energetic Basis of Ion Selectivity
K+ energy balance:
Dehydration versus
Carbonyl oxygen resolvation in selectivity-filter lining
Does tight K+ binding slow transport across the channel?

10. Electrostatic Repulsion Forces Pushes and Speeds K+ Through Ion Channel
Selectivity filter contains 4 binding sites
Ions move down the concentration gradient

11. Aquaporins: Water-Specific Pores
Hydrophobic pore with 2 Asn residues serving as a bridge as well as a H-bond disruptor
Side view
Top view

12. Gated Channels via Conformational Changes
Channels open or close in response to a specific signal such as: pH, voltage, Ca+2, or phosphorylation

13. Transport via Alternate Protein Conformations
Lactose permease ribbons blue to red (N- to C-terminus)
Black – lactose disaccharide
Space filling w/ 2 helices missing

14. Sodium Gradient Formed via a Na+-K+ ATPase Antiport Pump

15. Na+-K+-ATPase: Active Transport

16. Sodium Gradient Formed via a Na+-K+ ATPase Antiport Pump
P-type ATPases form a phosphorylaspartate and include:
Ca+2 ATPases for muscle contraction
Gastric H+-K+ ATPases
Link

17. Secondary Transport via a Common Sodium Concentration Gradient
Na+-K+ ATPase antiporter gradient drives:
Glucose import via a Na glucose symporter
Calcium ion export
via a Na+-Ca+2
antiporter

18. Digoxin Na+-K+ Pump Inhibition via Dephosphorylation Blocking
Digoxin – a cardiotonic steroid medication used for atrial fluttering and heart failure.
How can digoxin be chemically described?
Digitalis purpurea

19. Pufferfish: a Japanese delicacy and highly toxic
Na+ Channel Blocker
Pufferfish: a Japanese delicacy and highly toxic
Specific in blocking Na+ while having no effect on K+
Reversible binding: hydrated Na+ (nsec), tetrodotoxin (0.3 min)
Lethal dose in humans: 10 ng
How does this cork-like toxin position itself? Host-toxicity prevention mechanism?

20. Chapter 9 Problems: 11, 13, 17, 21, 25, 33 and 37