Chem 452 - Lecture 9
Pumps and Channels
111121
With this lecture we begin a unit a that looks at proteins as complex machines.
We will look first at the intrinsic membrane proteins that are responsible for
moving material across membranes. Those that require a source of free energy to
carry out the transport are called active transport systems. Some of these are
directly coupled to the hydrolysis of ATP, while others are coupled to a second
concentration gradient that flows across the cell in a favorable direction. We will
also look at gated passive transport systems, which, while requiring no external
source of free energy, are far from from being just simple channels.
Introduction!
✦
Membrane proteins function as
•
Pumps (Chapter 13)
•
Channels (Chapter 13)
•
Signal transducers (Chapter 14)
•
Energy transducers (Chapter 18 & 19)
Chem 452, Lecture 9 - Pumps and Channels
2
Introduction!
✦
Membrane proteins function as
•
Pumps (Chapter 13)
•
Channels (Chapter 13)
•
Signal transducers (Chapter 14)
•
Energy transducers (Chapter 18 & 19)
Chem 452, Lecture 9 - Pumps and Channels
3
Membrane Lipids and Water
✦
Lipid membranes display a wide range of
permeability's to small molecules.
Chem 452, Lecture 8 - Lipids and Cell Membranes
4
Introduction!
✦
Pumps and Channels move substances across
membranes.
•
Pumps move substances from regions of low
concentration to high concentration.
Requires a source of energy (active transport)
Channels allow substances to move from regions of
high concentration to low concentration.
‣
•
‣
‣
Does not require a source of energy (passive
transport)
If passive transport requires a channel it is
called facilitated diffusion.
Chem 452, Lecture 9 - Pumps and Channels
5
Introduction!
✦
✦
Some pumps couple transport to the hydrolysis
of ATP.
•
P-Type ATPases
•
ATP-binding cassette (ABC) transporters
Some pumps couple transport to a second
concentration gradient (secondary transport)
Chem 452, Lecture 9 - Pumps and Channels
6
Introduction!
✦
Transporters are used to regulate the metabolic
activity of a cell.
•
e.g. Glucose Transporters
Chem 452, Lecture 9 - Pumps and Channels
7
Introduction!
✦
Gated channels, while requiring not energy for
transport, can be highly specific.
The Potassium Channel
Chem 452, Lecture 9 - Pumps and Channels
8
Active versus Passive Transport!
✦
Transport across membranes
•
Simple Diffusion (passive transport)
•
Facilitated diffusion (passive transport)
•
Requires energy (active transport)
Chem 452, Lecture 9 - Pumps and Channels
9
Active versus Passive Transport!
✦
The free energy change required for active
transport depends on
•
Concentration differences
•
Voltage differences
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
Chem 452, Lecture 9 - Pumps and Channels
10
Active versus Passive Transport!
✦
The free energy change required for active
transport depends on
•
Concentration differences
•
Voltage differences
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
Concentration
Chem 452, Lecture 9 - Pumps and Channels
10
Active versus Passive Transport!
✦
The free energy change required for active
transport depends on
•
Concentration differences
•
Voltage differences
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
Concentration
Chem 452, Lecture 9 - Pumps and Channels
10
Active versus Passive Transport!
✦
The free energy change required for active
transport depends on
•
Concentration differences
•
Voltage differences
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
Concentration
Chem 452, Lecture 9 - Pumps and Channels
10
Active versus Passive Transport!
✦
The free energy change required for active
transport depends on
•
Concentration differences
•
Voltage differences
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
Concentration Voltage
Chem 452, Lecture 9 - Pumps and Channels
10
Active versus Passive Transport!
✦
The free energy change required for active
transport depends on
•
Concentration differences
•
Voltage differences
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
Concentration Voltage
Chem 452, Lecture 9 - Pumps and Channels
10
Active versus Passive Transport!
✦
The free energy change required for active
transport depends on
•
Concentration differences
•
Voltage differences
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
Concentration Voltage
Chem 452, Lecture 9 - Pumps and Channels
10
ATPase Pumps (Active Transport)!
✦
P-type ATPases
✦
ATP-Binding Cassette Transporters
Conformational changes are coupled to ATP hydrolysis
Chem 452, Lecture 9 - Pumps and Channels
11
ATPase Pumps!
✦
P-type ATPases
•
Na+/K+ ATPase
‣
Pumps 3 Na+ out while pumping 2 K+ in.
•
Gastric H+/K+ ATPase
•
Sarcoplasmic Ca2+ATPase (SERCA)
Chem 452, Lecture 9 - Pumps and Channels
12
ATPase Pumps!
✦
The energetics of active transport
•
Na+/K+ ATPase
‣
Pumps 3 Na+ out while pumping 2 K+ in.
-50 kJ/mol
(+)
-50 mV
(-)
3
14 mM
157 mM
2
143 mM
4 mM
Chem 452, Lecture 9 - Pumps and Channels
13
ATPase Pumps!
✦
The energetics of active transport
•
Na+/K+ ATPase
‣
Pumps 3 Na+ out while pumping 2 K+ in.
⎛c ⎞
ΔG = RT ln ⎜ 2 ⎟ + ZFΔV
⎝ c1 ⎠
⎛ ( 0.143)3 ( 0.157 )2 ⎞
kJ ⎞
kJ ⎞
⎛
⎛
= ⎜ 8.314 x 10 −3
⎟ ( 310 K ) ln ⎜
⎟ ( +0.050V)
3
2 ⎟ + ( +1) ⎜ 96.5
⎝
⎝
mol•K ⎠
mol•V ⎠
⎝ ( 0.014 ) ( 0.004 ) ⎠
kJ
kJ
+ 4.8
mol
mol
kJ
= 41.7
mol
= 36.9
Chem 452, Lecture 9 - Pumps and Channels
14
ATPase Pumps!
✦
SERCA (Sarcoplasmic Reticulum Ca2+ ATPase)
• Have crystal structure for each step in
pumping cycle
Chem 452, Lecture 9 - Pumps and Channels
15
ATPase Pumps!
✦
SERCA (Sarcoplasmic Reticulum Ca2+ ATPase)
• Have crystal structure for each step in
pumping cycle
Chem 452, Lecture 9 - Pumps and Channels
15
Chem 452, Lecture 9 - Pumps and Channels
16
Chem 452, Lecture 9 - Pumps and Channels
17
ATPase Pumps!
✦
SERCA
• Phosphorylation of
an aspartate (A351)
causes a
conformational
change that disrupts
the Ca2+ binding
sites.
ATPase Pumps!
✦
SERCA
ATPase Pumps!
✦
The drug digitoxigenin (digitalis), which is used
to treat congestive heart failure, inhibits the
Na+/K+ ATPase.
Chem 452, Lecture 9 - Pumps and Channels
18
ATPase Pumps!
✦
✦
The P-type pumps are homologous.
The drug digitoxigenin (digitalis), which is used
to treat congestive heart failure, inhibits the
Na+/K+ ATPase.
Chem 452, Lecture 9 - Pumps and Channels
19
ATPase Pumps!
✦
✦
The P-type pumps are homologous.
The drug digitoxigenin (digitalis), which is used
to treat congestive heart failure, inhibits the
Na+/K+ ATPase.
Foxglove (Digitalis purpurea)
Chem 452, Lecture 9 - Pumps and Channels
20
ATPase Pumps!
✦
✦
✦
The P-type pumps are homologous.
The drug digitoxigenin (digitalis), which is used
to treat congestive heart failure, inhibits the
Na+/K+ ATPase.
With higher cellular Na+ levels, the Ca2+ pump
is slower to remove the Ca2+ from the
cytoplasm, leading to a stronger contraction.
Chem 452, Lecture 9 - Pumps and Channels
21
ATPase Pumps!
✦
✦
✦
The P-type pumps are homologous.
The drug digitoxigenin (digitalis), which is used
to treat congestive heart failure, inhibits the
Na+/K+ ATPase.
With higher cellular Na+ levels, the Ca2+ pump
is slower to remove the Ca2+ from the
cytoplasm, leading to a stronger contraction.
Chem 452, Lecture 9 - Pumps and Channels
21
ATPase Pumps!
✦
The P-type pumps are homologous.
•
Yeast contain 16 examples
‣ H+
‣ Ca2+
‣ Na+
‣ Cu2+
‣ phospholipid (flipases)
Chem 452, Lecture 9 - Pumps and Channels
22
ATPase Pumps!
✦
The P-type pumps are homologous.
•
Yeast contain 16 examples
‣ H+
‣ Ca2+
‣ Na+
‣ Cu2+
‣ phospholipid (flipases)
Chem 452, Lecture 9 - Pumps and Channels
22
ATPase Pumps!
✦
The ATP-binding (ABC) Transporter.
•
Uses a slightly different strategy from the P-type
ATPases.
Chem 452, Lecture 9 - Pumps and Channels
23
ATPase Pumps!
✦
The ATP-binding (ABC) Transporter.
•
Uses a slightly different strategy from the P-type
ATPases.
lipid transporter
(Vibrio cholera)
Chem 452, Lecture 9 - Pumps and Channels
24
ATPase Pumps!
✦
The ATP-binding (ABC) Transporter.
•
Uses a slightly different strategy from the P-type
ATPases.
Chem 452, Lecture 9 - Pumps and Channels
25
Secondary Transporters!
✦
Secondary transporters are active transport
systems that do not derive their energy
directly from the hydrolysis of ATP
•
Instead, the active transport is coupled to the
passive transport of a second metabolite
Chem 452, Lecture 9 - Pumps and Channels
26
Secondary Transporters!
✦
Lactose Permease is a well-studied example.
Chem 452, Lecture 9 - Pumps and Channels
27
Secondary Transporters!
✦
The transport of lactose up a concentration
gradient is coupled to the transport of protons
down a concentration gradient.
Chem 452, Lecture 9 - Pumps and Channels
28
Secondary Transporters!
✦
The transport of lactose up a concentration
gradient is coupled to the transport of protons
down a concentration gradient.
Is lactose permase
a “symporter” or an “antiporter”?
Chem 452, Lecture 9 - Pumps and Channels
28
Next up
✦
Unit V, Lecture 9, con’d - Membrane Channels
and Pumps. (Chapter 13)
•
K+ channel and the action potential
Chem 452, Lecture 9 - Pumps and Channels
29